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The search for spin-reorientation (SR) phase transitions, a spontaneous rotation of ordered magnetic moments, in ferrimagnetic (FiM) materials, which carry a net magnetization, is of fundamental and practical interest for applications in the field of spintronics. In this work, we have investigated Mn self-doped (Er 0.7 Mn 0.3)MnO 3 solid solution with GdFeO 3 -type Pnma perovskite structure by combining specific heat, magnetic susceptibility and neutron powder diffraction measurements. We provide experimental evidence for FiM order below T C = 104 K, and a spontaneous SR transition at T SR = 11 K. A FiM structure appears in all (R 1-x Mn x)MnO 3 compounds with R = Dy–Lu for x ≥ 0.2. But in this structural family, R = Er is the only material with a SR transition. FiM order in (Er 0.7 Mn 0.3)MnO 3 appears with ferromagnetic (FM) ordering of Mn3+ and Mn4+ cations at the B site along the a -direction, which are antiferromagnetically (AFM) coupled with Er3+ and Mn2+ cations at the A site. At T SR , ordered Er3+ change direction from the magnetically harder a -axis to the magnetically easy b -axis and induce a change of the whole FiM structure, including the direction of all Mn spins from the irreducible representation m GM3+ to m GM4+. We calculated the crystal-field (CF) anisotropy for Ho3+ in (Ho 0.8 Mn 0.2)MnO 3 and Er3+ in (Er 0.7 Mn 0.3)MnO 3 , based on the point charge model; the results revealed large magnetic anisotropies. For the FiM structure of (Ho 0.8 Mn 0.2)MnO 3 , the magnetically easy a -axis of Ho3+ keeps the high-temperature magnetic directions along the a -axis and gives rise to a pronounced magnetization reversal effect at low temperature because of a significant rise of Ho3+ ordered moments. On the other hand, for the FiM structure of (Er 0.7 Mn 0.3)MnO 3 , the magnetically easy b -axis of Er3+ gives rise to a SR phase transition at T SR , which does not lead to magnetization reversal even though Er3+ ordered moments rise significantly at low temperatures. [ABSTRACT FROM AUTHOR]

Employing an advanced citrate precursor methodology, we successfully synthesized nanoscale spinel ferrites, denoted as Mg 1-x Zn x Fe 2 O 4 (where x ranges between 0.0 and 1.0) or MZFO. Comprehensive analysis, utilizing state-of-the-art X-ray diffraction (XRD) techniques, demonstrated the defining attributes of the crystal structure. All examined specimens consistently exhibited a singular phase, adopting a cubic crystalline architecture. XRD pattern analysis allowed us to deduce the average particle dimensions of these ferrite specimens, which span between 17.2 nm and 31.5 nm. This observed size distribution corroborates well with transmission electron microscopy (TEM) imagery estimations. Delving into the Fourier-transform infrared (FTIR) spectra, two distinctive absorption bands of ferrites emerged: the first between 540 and 570 cm−1 and the subsequent between 339 and 435 cm−1. To glean insight into the electromagnetic attributes of MZFO, we meticulously assessed the experimentally ascertained S-parameters. This scrutiny spanned a frequency spectrum of 8–18 GHz. It was inferred that electromagnetic wave energy dissipation arises chiefly from a combination of electrical and magnetic phenomena. The underlying mechanisms of electrical dissipation can be attributed to polarization processes. Concurrently, the magnetic energy losses predominantly stem from magnetization reversal dynamics. Notably, a substantial attenuation observed in the reflected wave energy, ranging between −10 and −18.5 dB, augments the potential for this material's integration into practical applications. [ABSTRACT FROM AUTHOR]

In this article, In3+ and Sc3+ ions dual-substituted NiCo nanospinel ferrites (ScIn →CoNi Fe 2 O 4 NSFs) have been synthesized through citrate-gel auto combustion method to investigate the effect of In3+ and Sc3+ ions on magnetic, and microwave characteristics. The following techniques TEM, SEM, EDX, and XRD were applied to characterize surface morphology, chemical composition, phase identification, and crystallinity of products, respectively. The XRD verified a phase formation of spinel structure with a minor amount of Sc 2 O 3 was observed for products having x ≥ 0.04. The average crystal size (D XRD) of the products was estimated within the 33–68 nm range using the Scherrer equation. SEM and HR-TEM analyses exhibited accumulating sphere-shaped particles. By fitting the room-temperature spectra obtained from Mössbauer spectroscopy (Moss), Hyperfine interactions were determined. The cation distribution shows that there is a migration of In3+ ions in the lattice in an A→B direction with increasing concentrations while the B site is preferred by the larger Sc+3. M−H plots for 300 and 10 K illustrated all products carried out with a ferrimagnetic character. An enhancement in saturation magnetization (M s) was remarked with Sc–In doping ratio up to 0.04 and thereafter a drop as the Sc–In concentration increased. The tendency in M s values might be described by correlating it to the cation distribution amongst O h and T d (octahedral and tetrahedral, respectively) sublattices. Temperature-dependent magnetization measurements were also investigated, which further confirmed the maintenance of the ferrimagnetic character throughout the temperature range 10–300 K. The peculiarities of the microwave properties have been analyzed by the measured S-parameters in the range of 6–18 GHz. It was assumed that the energy losses due to reflection are a combination of electrical and magnetic losses due to polarization processes and magnetization reversal processes in the region of inter-resonant processes. The average value of the reflection coefficient is −14.48 ... −14.24 dB. A significant attenuation of the reflected wave energy opens up broad prospects for practical applications as coatings for providing electromagnetic compatibility. [ABSTRACT FROM AUTHOR]

Magnetization reversal widely exists in ferrimagnets, which provides an opportunity to develop novel low-power-consumption memory in the future. In the present work, dense CaEuFeO 4 ceramics with the single-layered Ruddlesden–Popper structure were prepared by a standard solid-state reaction process. The orthorhombic phase was determined to have the space group Bmab at room temperature. The antiferromagnetic state was observed below the Néel temperature of 338 K, and temperature-induced magnetization reversal was observed below the compensation temperature in the field cooling protocol. Moreover, field-induced magnetization reversal or bipolar magnetic switching between different fields was also observed at low temperatures. The intriguing temperature- and field-induced magnetization reversal is induced by the competition between the canted Fe3+ moment and the antiparallel Eu3+ moment induced by the Eu–Fe exchange interaction. [ABSTRACT FROM AUTHOR]

SmCr 0.85 Mn 0.15 O 3 (SCMO) nanoparticles with Pnma space group have been synthesized by the sol-gel auto-combustion method with an average crystallite size of 70 nm. The structural analysis indicates a comparable unit cell volume with that of the bulk compound. The structural distortion is calculated by various factors such as cell distortion factor, octahedral distortion, dodecahedral distortion, strain and tolerance factor, which arise due to the Jahn-Teller (JT) effect and a tilting in the octahedra. The obtained distortion values suggest a larger distortion in the structure due to the nano-size effect compared with the bulk counterpart. The diffuse reflectance spectrum confirms the semiconducting nature of SCMO nanoparticles with an optical bandgap of 2.9 eV, higher than that of the bulk compound. The extinction coefficient of the SCMO nanoparticles exhibits a larger value than that of the bulk, suggesting a higher absorbing character of the nanoparticles. The temperature-dependent magnetization reveals a decrease in the Néel temperature on Mn substitution. The negative magnetization is also observed below the compensation temperature, T comp. Moreover, a stable magnetic switching behavior is demonstrated by varying temperatures under ZFC and FC protocols. The semiconducting nature and the stable magnetic switching behavior of SCMO nanoparticles make them suitable for optoelectronic, photovoltaic, and magnetic switching applications. Negative magnetization is induced with Mn substitution at Cr-site in SmCrO 3 nanoparticles. The bipolar magnetization switching is achieved by changing the temperature under field cooled (FC) mode. Similar switching is also obtained as a function of time at a fixed temperature of 23 K under FC & ZFC modes. [Display omitted] [ABSTRACT FROM AUTHOR]

The precipitation-hardened Sm-Co permanent magnets relied on the pinning of nanocellular structures to achieve high coercivity, and have an irreplaceable position in high-temperature applications. In this article, by employing micromagnetic simulations and magnetic domain observations, the pinning behavior of lamellar phases (Z-phase) were investigated, which has not been well understood before. The results showed that the Z-phase can serve as a strong pinning position, but due to the parallel lamellar distribution, the magnetic domain walls can move around. Additionally, the effect of Z-phase on coercivity was achieved by changing the morphology of magnetic domain walls during magnetization reversal. For attractive pinning, the coercivity was reduced by the Z-phase, while for repulsive pinning, the Z-phase increased the coercivity when γ Z ＜0.54γ H. Our findings can provide a novel understanding of the coercivity mechanism of precipitation-hardened Sm-Co permanent magnets. [Display omitted] • Lamellar phases can serve as a strong pinning position in Sm-Co magnets. • The coercivity was reduced by the Z-phase for attractive pinning. • For repulsive pinning, the Z-phase increased the coercivity when γ Z ＜0.54γ H. [ABSTRACT FROM AUTHOR]

The inverse spin Hall effect (ISHE) is a significant phenomenon that enables the conversion of spin current into charge current, offering promising applications in novel spintronic devices. In conventional ISHE measurements, it is widely recognized that the spin polarization, spin current, and generated charge current are mutually perpendicular. This study systematically investigates the ISHE in Pt/Co/Pt multilayers grown on a single-crystalline yttrium iron garnet (YIG) layer. A non-zero ISHE voltage was obtained along the direction parallel to the external magnetic field within the YIG coercive field range, deviating from the classical ISHE behavior. Our investigation revealed that the in-plane magnetic anisotropy of single-crystalline YIG plays a crucial role, as the easy axis of YIG and the external magnetic field collaboratively determine the polarization direction of the spin current, especially when the external magnetic field is smaller than the YIG coercive force. Furthermore, by tuning the small in-plane magnetization component of the Pt/Co/Pt multilayers, which couples with the YIG magnetization, we were able to control the shape and reversal path of the ISHE voltage loop. These findings deepen our understanding of how magnetic order affects charge current flow in ISHE measurements. The variety of ISHE voltage loop shapes and reversal paths observed suggest potential applications for this device as a magnetic field sensor. [ABSTRACT FROM AUTHOR]

Utilization of micromagnetic simulation is a very attractive subject to understand the magnetic behavior of nanowire arrays that tune their geometrical features and magnetic properties. Here, the micromagnetic simulations utilize to investigation of the single, and a 3 × 3 array of iron nanowires with diameters from 30 to 60 nm. The diameter size and the distance between the wires are selected according to the fabrication of iron nanowires grown in alumina templates. The simulation indicated that an increase in diameter led to a decrease in the coercive field and squareness ratio in both single nanowires and nanowire arrays. Besides, the simulation discloses that the magnetization reversal process of the nanowires with diameters more than 42 nm occurs through the nucleation and propagation of vortex domain walls. In the nanowires array, an increase in wire diameter increases the number of jumps in the hysteresis loop, indicating a more magnetic interaction between the nanowires. [ABSTRACT FROM AUTHOR]

• Four nona-coordinate mononuclear dysprosium zero-field single-molecule magnets derived from benzoxazole ligands is prepared. • Four complexes all behave as single-molecule magnets with effective energy barrier and butterfly shape magnetic hysteresis. • Ligand substituent group strategy of benzoxazoles can utilize to tune the magnetic anisotropy of nona-coordinate mononuclear dysprosium complexes. • Experimental structural data were correlated with computational results. • The order of ligand bulkiness (1 < 2 < 3 < 4) correlated with the strength of equatorial bonds, influencing the respective barrier heights (1 < 2 < 3 < 4). Taking advantage of modified substitution group strategy, the magneto-structural correlation of four nona-coordinate mononuclear dysprosium zero-field single-molecule magnets derived from benzoxazole ligands is established. Mixing of the corresponding benzoxazole ligands and dysprosium trifluoromethanesulfonate in the presence of methanol solvent yielded four nona-coordinate mononuclear dysprosium complexes 1 – 4 with the core molecular formula Dy(L x-R) 3 (R = F, 1 , x = 1; CN, 2 , x = 2; CF 3 , 3 , x = 3 and C(CH 3) 3 , 4 , x = 4). The coordination geometries of the dysprosium metal site with N 6 O 3 donor atoms in 1 – 4 are all belong to spherical capped square antiprism (C 4v) and the detailed corresponding parameters are 1.509, 1.173, 1.412 and 1.377, respectively. The static and dynamic magnetic susceptibilities measurements were performed on 1 – 4. They all display frequencies-dependent ac out-of-phase component signal peaks at different temperatures and zero external field, characteristic of single-molecule magnets behaviour. Variable-field magnetization measurements performed at 2 K confirm the magnetization blocking for 1 – 4 and reveal the presence of butterfly shape magnetic hysteresis. The experimental resulted effective energy barriers for magnetization reversal for 1 – 4 are 48.6, 102.2, 113.5, and 120.6 K, respectively. To understand the origin of variation observed, we have performed ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations on complexes 1 – 4. The calculations reveal axial g-tensors within the ground KD state, aligning with experimental results, and contributing to the observed trend in barrier heights. The computed crystal field parameters show an increasing trend from 1 to 4 , indicating strengthening axial bonds, while non-axial CF parameters decrease. Steric hindrance from bulky ligands correlates with weakened equatorial bond strength, further contributing to higher barrier heights. Additionally, the LoProp charge on axial atoms strengthens the bonds in the order 1 → 2 → 3 → 4 , reaffirming the importance of strengthen axial bond and weakening equatorial bonds towards better performant SIMs. Our work demonstrates that ligand substituent group strategy applied on benzoxazoles can utilize to tune the magnetic anisotropy of nona-coordinate mononuclear dysprosium complexes. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, using three-dimensional porous alumina (3D-AAO) as a template, Ni-Zn-In nanowires array with periodically changing diameters was successfully prepared by direct current electrodeposition method. The effect of deposition voltage on the morphology, crystal structure and magnetic properties of Ni-Zn-In ternary alloy nanowires was studied. The experimental results show that the diameters of the nanowires are 212 nm and 151 nm, and the periodic length is 800 nm, which matches the pore size of the phosphoric acid-etched 3D-AAO template. XRD results indicate that the crystal structure of Ni-Zn-In nanowires can be adjusted by the deposition voltage. The VSM results reveal that the Ni-Zn-In nanowires possess soft magnetic properties and significant magnetic anisotropy, with the easy magnetization direction parallel to the film. The nanowires deposited at −1.5 V exhibit the highest coercivity of 161 Oe and squareness of 0.045. Micromagnetic simulations show that the magnetization reversal mechanism of the Ni-Zn-In nanowires is localized nucleation mode. • Three-dimensional AAO films were prepared using Intermittent sawtooth current waves. • Ni-Zn-In nanowires with periodic diameter variation were prepared by direct current electrodeposition. • The effect of deposition voltage on crystal structure and magnetic properties of Ni-Zn-In nanowires was studied. • Ni-Zn-In nanowires has soft magnetic properties and magnetic anisotropy. • The magnetisation reversal mechanism of Ni-Zn-In is a combination of vortex rotation and coherent rotation. [ABSTRACT FROM AUTHOR]

• Sintered Nd-Fe-B sludge was purified to obtain purified sludge with a Nd 2 Fe 14 B phase. • Propose new strategies for ultra-short process recycling of GBD Nd-Fe-B sludge. • Break through the barrier of lower magnetic properties of regenerative magnets. • Low recycling cost and substantial reduction of recycling energy consumption. The grinding sludge of grain boundary diffusion Nd-Fe-B magnet is rich in heavy rare earth and has a typical core–shell microstructure. In this work, an ultra-short process was developed to realize green, in-situ regeneration of the sludge and efficient reuse of heavy rare earth elements. The regenerated magnets showed excellent magnetic performance and good temperature stability which were fabricated after the purification of sludge, composition regulation with rare earth-rich compounds, Nd 42.1 Fe bal B 0.79 , NdH x , (PrNd)H x , and sintering. Especially, the magnet prepared by using Nd 42.1 Fe bal B 0.79 alloy had significant property recovery, where remanence and coercivity were restored to 12.8 kG, and 20.6 kOe, respectively, reaching 97.7 % and 162.5 % of the original magnet. The magnetization reversal behavior and the coercivity mechanism were analyzed to keep the nucleation mechanism, and the high coercivity stemmed from the repair and optimization of the grain boundary by introducing rare earth-rich alloys, the full utilization of heavy rare earth elements, and the core–shell microstructure rooted in the sludge as well. [ABSTRACT FROM AUTHOR]

To create a high-density data storage system, a thorough understanding of magnetic domain interactions is essential. In this work, we present a systematic study of magnetic domain state interaction and switching mechanism of Fe–Co–Al films across various thicknesses. Structural analysis confirms the formation of an A2-type disorder structure. Magnetic investigation reveals that all films are soft magnetic in nature, exhibiting a predominant in-plane magnetic anisotropy with a low coercive field that increases from 1.9 mT to 3 mT as the film thickness grows from 5 nm to 25 nm. Analysis of first-order reversal curves reveals the formation of multi-domain (MD) states. An enhancement of magnetic domain interactions occurs as the contour graph shifts along the coercive field direction with an increase in film thickness. Switching field distribution (SFD) analysis reveals broader SFD curves, indicating more inter-grain interactions as magnetostatic interactions between magnetic grains intensify with thickness. Further, magnetic force microscopy analysis confirms the presence of MD structures in all films. Magnetization reversal dynamics elucidates domain wall pinning near to zero field and possesses a large out-of-plane switching field. Simulations are performed to corroborate experimental findings. These findings underscore the critical role of domain state configuration and switching mechanisms for designing spintronic devices using soft magnetic thin films. [Display omitted] • Fe–Co–Al thin films of varying thicknesses (5, 10, 15, and 25 nm) were deposited at room temperature on Si ¡100¿ substrate using DC magnetron sputtering technique. • Magnetic investigation reveals that all films are soft magnetic in nature, exhibiting a predominant in-plane magnetic anisotropy. • Analysis of first-order reversal curves reveals the formation of multi-domain states which is confirmed by magnetic force microscopy investigation. • Switching field distribution analysis reveals broader SFD curves, indicating more inter-grain interactions as magnetostatic interactions between magnetic grains. • Micromagnetic simulations supported the experimental findings of hysteresis loops and the existence of MD across all films. [ABSTRACT FROM AUTHOR]

The magnetic properties of bi-magnetic core/shell nanoparticles (NPs) have been a subject of extensive investigation. Yet, the role of shell thickness in hard/soft and soft/hard core/shell NPs, corresponding to conventional and inverse structures, remains incompletely elucidated. In this study, we synthesized two sets of core/shell NPs, namely Fe 3 O 4 @CoFe 2 O 4 (IF@CF) and CoFe 2 O 4 @Fe 3 O 4 (CF@IF), featuring a fixed core diameter of approximately 11 nm and varying shell thicknesses up to 5 nm. These NPs were synthesized via a seed-mediated particle growth approach. The formation of the core/shell configuration of typical NPs in both sets was directly verified through scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) imaging. Notably, the saturation magnetization (M S) of IF@CF NPs exhibited a significant increase compared to that of the IF core across all shell thickness variations, whereas it remained largely unchanged for CF core and CF@IF NPs. Conversely, the coercivity (H C) showed an opposite trend in the two structures with increasing shell thickness. We observed the emergence of a transition from constricted to smooth hysteresis loops in the conventional structure when the shell thickness reached 5 nm. The systematic evolution of hysteresis loops with escalating shell thickness in both structures closely correlates with distinct magnetic reversal mechanisms, influenced significantly by interparticle interactions. Our study presents a pathway for modulating the magnetic properties of bi-magnetic core/shell NPs, thereby opening avenues for advanced applications in magnetic imaging, sensing, drug delivery, and magnetic hyperthermia. • Two sets of Fe 3 O 4 @CoFe 2 O 4 and CoFe 2 O 4 @ Fe 3 O 4 core/shell NPs were synthesized via a seed-mediated particle growth approach. • The formation of the core/shell structure of typical NPs was directly verified through STEM-EDS imaging. • The systematic evolution of hysteresis loops with escalating shell thickness influenced by interparticle interactions. [ABSTRACT FROM AUTHOR]

We investigated the magnetic properties of the Heusler alloy NiMnSn grown on thermally oxidized Si (100) by performing magnetic hysteresis measurements using the Polar Magneto-Optical Kerr Effect (PMOKE) technique. For a thickness of 30 nm, the NiMnSn alloy demonstrates out-of-plane magnetic anisotropy. We observed clear exchange bias, which we attribute to the exchange coupling between the spin glass and ferromagnetic phases. Our study also revealed that the growth of a 1 nm thick Heusler alloy NiMnSn layer on a cobalt layer with perpendicular anisotropy enhances the perpendicular magnetic anisotropy. However, we observed an antagonistic effect with thicker Heusler layers, resulting in a loss of perpendicular anisotropy and the appearance of an exchange bias (EB). • A highly textured NiMnSn Heusler alloy was deposited by electron beam evaporation. • The polar Magneto-Optical Kerr Effect shows an out-of-plane anisotropy and room temperature exchange bias. • The NiMnSn alloy exhibits out-of-plane magnetic anisotropy for a thickness of 30 nm. • 1 nm thick Heusler alloy NiMnSn layer grown on a cobalt layer leads to an improvement in perpendicular magnetic anisotropy. [ABSTRACT FROM AUTHOR]

FeNi nanowires (NWs), 40 nm in diameter, were grown by electrodeposition. Compositional analysis showed Fe anomalous co-deposition, with different trends across the different potentials and electrolytes used. Those trends were explained within a modified Bocris-Drazic-Despic chemical reactions model, highlighting the importance of the electrochemical theory in understanding Fe-Ni electrodeposited systems. Structural characterization showed a change from a body-centred cubic structure for Fe-rich NWs to face-centred cubic at mid and low Fe content. Magnetic hysteresis measurements showed a range of coercivities from 20 mT for Fe-rich to 100 mT for Ni-rich NWs. Angular measurements allowed to determine that the magnetization reversal mechanism was dominated by transverse domain wall reversal. The analysis also hinted at the non-shape anisotropy acting as a demagnetizing force. First-order reversal curves (FORCs) showed that arrays with a high absolute value for the non-shape anisotropy had higher magnetic interactions, and vice versa. The non-shape anisotropy is dominated by the magnetostatic interactions between NWs, causing a weakening of the magnetic hardness. In combination with the coercivity angular measurements, the FORC analysis explained the shift in easy axis preference depending on NW chemical composition observed in the hysteresis loops of the samples. [Display omitted] • Electrochemical growth of Fe-Ni nanowires using different potentials and electrolytes. • Fe anomalous co-deposition explained within a modified Bocris-Drazic-Despic model. • Magnetization reversal process dominated by transverse domain wall. • FORC analysis showed increased magnetic interactions among nanowires for higher Fe content. • Magnetostatic interactions dominate the non-shape anisotropy and its demagnetizing effect. [ABSTRACT FROM AUTHOR]

We have investigated the phenomenon of negative magnetization and exchange bias effect in polycrystalline La 0.3-x Lu x Pr 0.7 CrO 3 (0 ≤ x ≤ 0.3). La 0.3 Pr 0.7 CrO 3 exhibits negative magnetization and positive exchange bias field below compensation temperature under an applied field of 1 kOe in field cooling mode due to the antiferromagnetic coupling between Pr3+ moment and canted Cr3+ moment with Cr3+ moment parallel to the direction of applied magnetic field. However, the phenomenon of negative magnetization disappears accompanied by a sign reversal of exchange bias field from positive to negative at low temperature for x ≥ 0.2 samples, which can be ascribed to the dominant role of G z F x order induced by Lu3+ doping and consequent spin rotation of Pr3+-Cr3+ coupling. Though the negative magnetization can still be observed for the x = 0.1 sample, negative exchange bias field occurs as the growth of G z F x ordering domain during the initial magnetization process, evidenced by the disappearance of negative magnetization and spin rotation of Pr3+-Cr3+ coupling after high magnetic field pulse. [Display omitted] [ABSTRACT FROM AUTHOR]

• Mechanism of magnetization reversal investigated in NiFe-nanodots. • This study performed by varying the strength of out-of-plane magnetic anisotropy. • Critical anisotropy value identified to stabilize the magnetic vortex state. • Energy values estimated at nucleation field, annihilation field and remanent states. • Analysis useful in estimating the energy barrier for the magnetization reversal. We thoroughly investigated the stability of vortex magnetization in Permalloy (Py) circular nanodots with and without magnetocrystalline anisotropy using micromagnetic simulations. This study explores a wide-ranging understanding of influence of anisotropy on hysteresis loops, and spin-configurations, and provides a detailed analysis of the energy profile. The ground state vortex configuration considered of size 64 × 20-nm2 Py-nanodot at zero out-of-plane anisotropy had been modulated till the anisotropy 250 kJ/m3. We analyzed different energy terms at nucleation field, annihilation field and remanent states to gain deeper insights into the magnetization reversal mechanism. The energy analysis revealed an interplay between exchange and demagnetization energies, resulting in the stability of vortex up to a critical anisotropy (C K) 170 kJ/m3. Beyond this C K , the vortex destabilizes, switching the magnetization to a single-domain state. Additionally, we estimated the energy barrier involved in single domain to vortex state transformation. These findings provide valuable insights for designing vortex-based magnetic data storage and memory devices. [ABSTRACT FROM AUTHOR]

• SmCo/Fe and SmCo/Co magnetic bilayer models are proposed. • The influence of the thickness of the magnetic layers is explored. • Our models are shown to describe well of experimental data. The magnetic SmCo/Fe and SmCo/Co heterostructures were numerically investigated in an external magnetic field using the micromagnetic simulation package MuMax3. The magnetization reversal curves and magnetic phase diagrams for these structures were plotted for different thicknesses of the magnetic layers and directions of the external magnetic field. The SmCo(20 nm)/Fe(20 nm) heterostructure reached saturation along the hard magnetization axis at an external magnetic field of 18 T, while a single SmCo(20 nm) layer achieved saturation at 18.2 T. The highest values of (BH) max were found to be 29.2 MG∙Oe for the SmCo(20 nm)/Fe(10 nm) and 35.5 MG∙Oe for the SmCo(20 nm)/Co(20 nm) heterostructures. [ABSTRACT FROM AUTHOR]

A new n = 2 Ruddlesden-Popper (RP) series La 2 SrFe 2- x Cr x O 7 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) has been prepared via Sol-gel Pechini method, and their structural, optical, and the magnetic characterization was done. Furthermore, we are for the first-time reporting on the photo-catalytic degradation of a dye by a complete n = 2, La 2 SrFe 2- x Cr x O 7 RP series. Rietveld refinement analysis confirms the formation of single-phase compounds with tetragonal crystal symmetry and I 4/ mmm space group. The results indicate a steady decrease in unit cell parameters and cell volume with Cr3+ doping. Dominant anti-ferromagnetic (AFM) interactions were observed in all the phases and the appearance of weak ferromagnetic (FM) interactions takes place owing to the Fe3+―O―Cr3+ FM interaction with Cr3+ doping. The χ M − F C curve for x = 0.8 phase shows the magnetization reversal (MR) phenomenon and becomes zero at T comp ∼127 K and the value becomes negative on further decreasing the temperature. The MR phenomenon is discussed in terms of the competing Fe3+―O―Fe3+, Fe3+―O―Cr3+, and Cr3+―O―Cr3+ super-exchange interactions. Enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) dye was obtained for x = 0.2 substituted phase, displaying a ∼99% degradation of dye in 30 min followed by ∼83%, ∼75%, ∼64% and ∼61% by x = 0.4, 0.0, 0.8 and 0.6 phases respectively in the same time interval. The results are explained in terms of crystallite size, the narrowing of band gap with Cr3+ substitution, and based on of recombination of charge carriers which, are in good agreement with the results of Photoluminescence (PL) emission intensity spectra. [ABSTRACT FROM AUTHOR]

The coercivity mechanism and magnetization reversal process of anisotropic La-Nd-Dy-Fe-B micron-sized films have been investigated. By varying the thickness of the single-layer film from 500 nm to 6 μm, the highest coercivity of 1.88 T in the film with 3 μm thickness is achieved at 300 K, due to the large dipole interaction and domain pinning effect. When the thickness is further increased to 6 μm, the coercivity decreases sharply to 1.11 T due to the microstructure and phase formation in the film. In the 6 μm multilayer film, the addition of a Ta spacer layer further enhances perpendicular magnetic anisotropy, the dipole interaction, and adjusts the phase distribution, collectively boosting the coercivity of the micron-sized film (1.63 T). As thickness of the film increases, the dominant mechanism of coercivity shifts from a pinning mechanism to a nucleation mechanism. This study contributes to the understanding of the coercivity mechanism and magnetization reversal process in La-Nd-Dy-Fe-B permanent magnet micron-sized films. [ABSTRACT FROM AUTHOR]

• The utilization efficiency of Tb is 11.8 kOe/% with 3 % (Pr 20 Nd 80) 60 Tb 15 Cu 15 Ga 10 addition, being higher than previous articles. • The synergy of Tb-rich matrix shell and antiferromagnetic Nd/Pr-rich GBP promotes the enhanced coercivity and thermal stability with high Tb utilization efficiency. • Micromagnetic simulation proves a maximum coercivity can be achieved at a low Tb concentration of matrix shell in the antiferromagnetic GBP model. Intergranular addition using heavy rare earth (HRE) Dy/Tb containing alloys has been an effective way to modulate the microstructure and chemical distribution towards fabricating high-coercivity Nd-Fe-B sintered magnets. In this work, (Pr 20 Nd 80) 60 Tb 15 Cu 15 Ga 10 (at%) intergranular alloy powders were designed and introduced with dual purposes of forming Tb-rich matrix shell and antiferromagnetic RE 6 Fe 13 Ga grain boundary phase (GBP). With 3 wt% (Pr 20 Nd 80) 60 Tb 15 Cu 15 Ga 10 addition, the coercivity H cj is significantly increased from 11.1 kOe to 17.9 kOe, accompanied with a high utilization efficiency of Tb (11.8 kOe/%) and a superior temperature coefficient of coercivity β (−0.531%/K). Microstructural analysis suggests that the improved wettability of grain boundary by (Pr 20 Nd 80) 60 Tb 15 Cu 15 Ga 10 addition is beneficial to form the Tb-rich matrix shell and antiferromagnetic RE 6 Fe 13 Ga GBP throughout the bulk magnets. Micromagnetic simulation is implemented to study the effect of formed ferromagnetic/antiferromagnetic GBP and Tb-rich matrix shell on the magnetization reversal process. Results show that the synergy of Tb-rich shell surrounding Nd/Pr-rich core and antiferromagnetic Nd/Pr-rich RE 6 Fe 13 Ga GBP is an effective way to promote the coercivity with high utilization efficiency of HRE Tb. [ABSTRACT FROM AUTHOR]

The compound Ca 2 MnTiO 6 , synthesized using a two-step solid-state reaction method, has been studied for its structural, spectroscopic (XPS) and magnetic properties, as part of our efforts to understand the correlation between mixed metal oxide bonds and magnetism in double perovskite oxides. Room temperature diffraction studies shows that the compound is in orthorhombic structure at room temperature and remains so till low temperatures, although the variation in global instability index (GII) indicated little instability of the structure as the temperature is lowered from room temperature (∼300 K) to 3 K. The compound exhibits interesting behavior in magnetic susceptibility, as it exhibits magnetization reversal or negative magnetic susceptibility at low applied fields which turns positive for higher fields. Magnetic susceptibility also exhibits two anomalies at T N1 ∼ 8.2 K and another one around, T N2 , between 121 – 124 K. Magnetization as a function of field reveals weak antiferromagnetism in the system, as M varies non-linearly, but sluggishly below T <150 K, with no signature of saturation with respect to H. Overall, magnetization studies show that there is inherent magnetic frustration in the system and lack of long-range magnetic order, which is supported by low temperature neutron diffraction studies too. The XPS studies quantify the oxidation states of mixed valent Mn and Ti. A comparison of the structural and physical properties of double perovskite compound is presented here to understand the strong correlation between structural, spectroscopic and magnetic properties. [ABSTRACT FROM AUTHOR]

Nanostructured magnetic materials have gained great interest due to their possible technological applications in electronic and spintronic devices or in medicine as drug carriers. The key issue which decides on their potential industrial utilization is an exhibited type of a magnetization reversal process. Two main approaches used to describe the switching mechanism are the domain wall motion and coherent magnetization rotation, known as the Kondorsky and Stoner–Wohlfarth models, respectively. The reversal modes can be distinguished by angular measurements of hysteresis loops; however, in many experimental reports the dependencies do not precisely follow either of the models. This makes the question of how the magnetization reversal takes place and how to control or modify it one of the unclear and worth investigation issues in the research on magnetic materials. In this paper, we present our studies on the magnetization reversal in the exchange-biased CoO/[Co/Pd] thin films deposited on a flat substrate and on an array of anodized titanium oxide nanostructures. We studied the reversal mechanism using hysteresis loops and First-Order Reversal Curves. Interestingly, instead of the typical for the flat Co/Pd multilayers Kondorsky process, the system shows a crossover between the domain wall motion and the coherent rotation. A similar situation takes place for the pattern sample. Here, we connect this unusual behavior with the interface exchange interaction responsible for the exchange bias effect. [Display omitted] [ABSTRACT FROM AUTHOR]

Ni 2 CrBO 5 has been synthesized and investigated by X-ray diffraction, dc magnetization, and specific heat measurements. The unusual cation distribution has been established: the M1 and M3 sites are occupied by Ni 2 + ions, the M2 site is by Cr3＋ ions, and the M4 site is mixed, featuring both Ni 2 + and Cr3＋ ions. The magnetic order onsets at T N = 140 K, which is confirmed by a λ -type peak in specific heat, followed by the dome-shaped anomaly of the magnetization at about 30 K. In the magnetically ordered state, a remarkable sequence of temperature-induced magnetization reversal sensitive to the measurement's regime is observed. Dominant antiferromagnetic interactions are characterized by the Weiss temperature θ = −73 K. The effective magnetic moment of 5.37 μ B per formula unit is close to the spin-only one. The effect of the cation distribution on the magnetic properties is discussed. • Phase-pure Ni 2 CrBO 5 with a ludwigithe structure was obtained using a solid-state reaction in two stages. • The compound has morphology in the form of elongated bars and needles. • Powder X-ray diffraction study has shown an orthorhombic crystal structure and unusual distribution of Ni 2 + and Cr 3 + ions over symmetry inequivalent metal sites. • The magnetization and specific heat measurements have revealed the compound undergoes magnetic phase transition at T N =140 K. [ABSTRACT FROM AUTHOR]

Advanced nanofabrication exploiting e-beam lithography has been used to prepare nanocomposites consisting of periodic arrays of soft magnetic FeCo-based nano-inclusions of variable dimensions, embedded in a hard magnetic FePt matrix. Nanocomposites with non-magnetic (Pt) inclusions and single phase hard magnetic FePt microstructures were prepared as reference samples. The formation of Kirkendall voids in the soft-in-hard nanocomposites, because of annealing-induced diffusion, has been identified through high resolution imaging and chemical analysis. Replication of the μ m-scaled nanocomposite and hard magnetic units over mm-scaled surfaces allowed global magnetic characterisation of magnetisation reversal using standard magnetometry. Magnetic force microscopy imaging was used for spatially resolved magnetic characterisation in different remanent magnetic states. Both of these experimental techniques were used to study the influence of the size, volume content and nature of the nano-inclusions on magnetisation reversal. The well-defined geometry and nano-scaled size of the inclusions render these nanocomposites as model systems for micromagnetic simulations and very good agreement was achieved between measured and simulated magnetisation reversal curves. This accordance motivates future in-silico optimisation of such soft-in-hard nanocomposites, which may serve as model systems to guide the design of new high performance bulk magnets which are less dependent on critical elements. [Display omitted] • Advanced nanofabrication used to prepare model nanocomposites consisting of periodic arrays of soft magnetic nano-inclusions of variable dimensions in a hard magnetic matrix. • Very good agreement achieved between experimentally probed and simulated magnetisation reversal. • Magnetic force microscopy enabled spatially resolved imaging, clearly identifying the soft and hard magnetic phases in different remanent states. [ABSTRACT FROM AUTHOR]

Large SmCo 5 single-crystal spheres are used as simple model objects for both theoretical and practical studies of the coercivity mechanism in permanent magnets (PM). These samples exhibit coercivity values exceeding 1 T, achieved through the enhancement of surface smoothness. The morphology and magnetic results indicate that surface defects play a key role in the reversal mechanism and nucleation process. The reversal mechanism and coercivity are studied by means of different magnetization protocols, shedding light on the influence of two types of nucleus of reversal magnetic domains. We then utilize these objects to probe the angular dependence of coercivity. Our examination of samples with differing surface states reveals that enhanced surface smoothness corresponds to a behavior closer to the coherent rotation model. This study underscores the massive influence of surface defects on magnetization reversal. Thus, the reduction of imperfections in PM grain boundaries holds the potential to significantly increase the nucleation field and thus the coercivity. More generally, our study introduces a methodology for examining the magnetization reversal of permanent magnets using simple model objects. • Coercivity surpassing 1 T in large SmCo5 magnets through electrochemical polishing. • Dominating nucleus type and their influence on magnetization reversal is revealed. • Effect of magnetization protocol on reversal magnetization. • Investigation of angular dependence of coercivity model using ideal objects. [ABSTRACT FROM AUTHOR]

• Permalloy (Ni 80 Fe 20) nanotubes (NTs) are fabricated using Anodic Aluminum Oxide (AAO) templates by using dc electrodeposition method. • Ni 80 Fe 20 grows in FCC crystal structures and which is clearly polycrystalline nature. • Magnetic properties of Ni 80 Fe 20 NTs are strongly influenced by annealing temperature. • H C Vs θ and SQ Vs θ with bell shape behavior verifies the easy axis of magnetization along the direction perpendicular long axis of tube. • After annealing, the increase in H C can be explained based on the Prolate ellipsoid chains model. One dimensional Permalloy (Ni 80 Fe 20) nanotubes (NTs) were successfully fabricated using Anodic Aluminum Oxide (AAO) templates with 100 nm diameter by employing a low-cost electrodeposition route at room temperature. As prepared Ni 80 Fe 20 NTs morphology, elemental analysis and structural details have been investigated by using field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and X-Ray diffraction (XRD) respectively. The structure of prepared Permalloy nanostructures has face centered cubic (FCC) phase with polycrystalline in nature. The Ni 80 Fe 20 NTs were annealed at 200 °C, 400 °C and 600 °C. The vibrating sample magnetometer (VSM) measurements showed that all the samples exhibit ferromagnetic nature. Furthermore, VSM has been employed to study the saturation magnetization (M S), Squareness (SQ) and Coercivity (H C) as the function of annealing temperature. A comparative study of magnetization reversal mechanism has also been conducted. The easy axis lies in the direction perpendicular to the NTS axis due to the dominance in shape anisotropy. Annealing temperature improved the magnetic properties of Permalloy (PA) NTs. This work will provide significant applications in the field of spintronics and high-density data storage devices. [ABSTRACT FROM AUTHOR]

The Mn 5 Ge 3 exhibits a wide range of fascinating properties such as high spin polarization up to 42 %, large spin diffusion lengths, near-room Curie temperature, and possible integration with Ge, GaAs, and Si substrates. The influence of substrate orientation on magnetic behavior has been investigated. The thin films studied present an in-plane magnetic reversal which is isotropic in samples grown on GaAs(111) and anisotropic in samples grown on GaAs(001). Another difference observed is a linear trend to saturation on the out-of-plane hysteresis loop in samples grown on GaAs(111), comparatively to samples grown on GaAs(001). To better understand this scenario, Density Functional Theory (DFT) calculations were conducted. The results indicate a ferromagnetic metallic ground state with properties that are consistent with the experimental results. The projected densities of states indicate that the main responsible for the magnetic moment observed in the Mn 5 Ge 3 is the Mn-Mn interaction. The magnetic field distribution isosurfaces obtained from the DFT calculations offer a satisfactory explanation of the magnetic reversal experimentally observed, especially the in-plane magnetic behavior in samples grown on both GaAs(111) and GaAs(001) substrates. This work provides a theoretical-experimental approach that allows a deeper understanding of the magnetic anisotropy behavior under the influence of the crystallographic orientation of the substrate observed in nearly-stoichiometric Mn 5 Ge 3 thin films, which is a good candidate for rare-earth free magnet in spintronic applications. [Display omitted] • Magnetic behavior of Mn 5 Ge 3 thin films grown on different substrates, such as GaAs(001) and GaAs(111). • Experimental measurements & DFT calculations explored the influence of substrate on the magnetic anisotropy of thin films. • The thin films exhibit in-plane magnetization reversal, which is isotropic for GaAs(111) and anisotropic for GaAs(001). • The magnetic behavior is attributed to the Mn-Mn interactions and the magnetic field distribution around the Mn atoms. • DFT analyses explain the experimental results and provide insight into the Mn 5 Ge 3 films' magnetic properties. [ABSTRACT FROM AUTHOR]

A systematic study of the dependence of the Grain Boundary Diffusion Process (GBDP) on texture using Dy and Dy-Nd-Cu in microcrystalline sintered and nanocrystalline hot deformed Nd-Fe-B magnets was performed. Diffusion parallel or perpendicular to the texture direction, the nominal c-axes orientation in the polycrystals, was investigated. By measuring thin slices from the respective samples, coercivity as a function of (i) magnet thickness and (ii) diffusion depth was obtained showing that GBDP efficiency depends on the diffusion direction, diffusion source as well as the grain morphology originating from the magnet production route. In nanocrystalline hot deformed magnets perpendicular diffusion is superior due to the platelet-like shape of the grains. Microcrystalline sintered magnets consist of equiaxed grains hence the main effects originate in anisotropic lattice diffusion and pole surface hardening. The magnetic properties are correlated with a comprehensive analysis of microstructure, chemistry and magnetization reversal. • Comparing texture's effect on GBDP in Dy, Dy-Nd-Cu in microcrystalline sintered & nanocrystalline hot deformed magnets. • GBDP efficiency relies on diffusion direction, source, and grain morphology from the magnet production route. • Perpendicular diffusion is more effective in hot deformed (nanocrystalline) magnets due to their platelet-like grain shapes. • Comprehensive analysis links magnetic properties with microstructure, chemistry, and magnetization reversal studies. [ABSTRACT FROM AUTHOR]

Macroscopic demagnetization in sintered Nd-Fe-B magnets by Tb grain boundary diffusion (GBD) is investigated in comparison with non-GBD ones. Demagnetization curves, the coercivity distributions, Tb content, and magnetic fields of the magnets at various external fields (μ 0 H ext) are analyzed. As μ 0 H ext approaches coercivity of the GBD magnet, S-N poles form near the center, between and parallel to the original N-S poles, indicating the magnetization reversal near the center of the GBD magnet. This is distinguished from the non-GBD magnets where demagnetization occurs mainly in the pole surfaces. The mechanism for macroscopic demagnetization is discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present work, [Co (1-(x + y)) Mg x Ni y ][Cr 2 ]O 4 (CMNCr)(where, x = y = 0, 0.10, 0.20) NPs are examine in detail by using experimental results. Solution combustion method is adopted to prepare the CMNCr NPs. Experimental results were studied to understand structure (using XRD), microstructure (using SEM) and magnetic behaviour (using SQUID). The structural analysis was confirmed a single-phase spinel cubic structure with singular structural distortions associated with Mg–Ni doping and the generation of metal vacancies. SEM micrographs of all samples reveal their highly porous nature. EDS was utilized to examine the elemental analysis of the samples. The formation of spinel cubic structure without impurity were also confirmed by Fourier-transform infrared (FTIR) spectroscopy and the same tool is used to investigate the absorption bands related to the A-site and B-site. For all samples, paramagnetic phase to ferrimagnetic phase transition observed at T C and conical spiral spin order transition observed at T S. The curie temperature is found to be 98 K, 89 K, and 85 K for [Co][Cr 2 ]O 4 , [Co 0.8 Mg 0.1 Ni 0.1 ][Cr 2 ]O 4 and [Co 0.6 Mg 0.2 Ni 0.2 ][Cr 2 ]O 4 samples, respectively. The spiral transition temperature is found to be 26 K, 14 K and 8 K for [Co][Cr 2 ]O 4 , [Co 0.8 Mg 0.1 Ni 0.1 ][Cr 2 ]O 4 and [Co 0.6 Mg 0.2 Ni 0.2 ][Cr 2 ]O 4 samples, respectively. All of the samples exhibit paramagnetic behaviour above T C. The negative magnetization effect were observed in [Co 0.6 Mg 0.2 Ni 0.2 ][Cr 2 ]O 4 NPs. 20% of Mg and 20% of Ni substitution to Co site in [Co][Cr 2 ]O 4 leads to the evident magnetization reversal at the compensation temperature with an applied magnetic field of 100 Oe. The M − H loop at 10 K exhibits large coercivity due to the spiral spin ordering. This phenomenon of negative magnetization in the material results in a stable state of magnetization in the material, which has significant applications in the field of magnetic storage devices. [ABSTRACT FROM AUTHOR]

We report the successful growth of BaFe 12 O 19 –BaTiO 3 (BaM-BTO) bilayer thin films using pulsed laser deposition, considering different crystallographic textures; BTO on (0001)-BaM and BaM on (100)-BTO. Our study involved the bilayers, the individual ferrite and titanate films, and the targets used in their growth. Raman spectroscopy and X-Ray diffraction were used to examine the structure of BaM-BTO thin films, indicating that there is no formation of impurity phases. The morphological characterization was made by scanning electron microscopy, and the magnetic behaviour was studied using SQUID magnetometry. The spontaneous magnetization, magnetic anisotropy constant, and anisotropy field were determined simultaneously from the magnetic hysteresis loop. In addition, we also studied the influence of different annealing temperatures over the magnetic behaviour of bare BaM and covered with BTO thin film. This allows to discern between the different magnetization reversal processes in bilayer systems, indicating a strong correlation between the anisotropy field and the coercive field, and an unusual linear relation of the anisotropy constant with the spontaneous magnetization. Our results indicate a direct influence of the BTO on the magnetic properties of the BaM phase, which places these composite bilayers as excellent candidates for the development of multifunctional devices. [ABSTRACT FROM AUTHOR]

The fundamental contribution of the Ta layer to the highly coercive Ta/SmCo / Ta films was investigated. A room temperature coercivity value of 4.5 T was achieved in film with 60 % SmCo 5 and 40 % Sm 2 Co 17. In films, in which only the Sm 2 Co 17 phase was observed in XRD (X-ray diffraction), a high coercivity of 2 T was also obtained. All films were obtained by codeposition at temperature environment of Sm and Co atoms on a Ta layer, followed by annealing to promote the crystallization of the Sm-Co film. The following results were observed: (i) the presence of voids in the Sm-Co layer, observed in the cross- section STEM (Scanning Transmission Electron Microscope) images, (ii) the presence of stable Ta α phase, observed in the XRD analysis, (iii) Ta diffusion in the Sm-Co layer, identified in the XPS (X-ray Photoelectron Spectroscopy) deep profile and, (iv) the initial magnetization curve, typical of a magnetization reversal controlled by pinning that led us to conclude that the voids produced during annealing by the diffusion of Ta in the Sm-Co layer, and they act as a pinning for the magnetization inversion, resulting in highly coercive films. Ta diffusion promoted the transition from the metastable Ta β phase to the stable Ta α phase, at temperatures below 800 ◦C. Another important result was the strong exchange interaction between the grains reflected in the square hysteresis with M r /M s ≈1. [Display omitted] • High coercivity in SmCo 5 and Sm 2 Co 17 films deposited on a buffer layer. • Ta diffusion in Sm-Co layer during annealing. • Voids in Sm-Co layer created during Ta diffusion in this layer. • Voids in the Sm-Co layer act as pinning to magnetization inversion. [ABSTRACT FROM AUTHOR]

Cylindrical nanodisks typically exhibit in-plane magnetization reversal comprising of nucleation and propagation of a vortex closure state. Present work investigates the magnetization reversal process in a cylindrical disk of radius ranging from 20 nm to 100 nm in which the flat surfaces at top and bottom are modified to convex shaped surfaces. It is found that the nucleation of vortex state no longer occurs as a result of this surface modification. Instead, a buckled magnetization state is nucleated which transforms to reverse buckled state yielding a square hysteresis loop. However, the out-of-plane hysteresis loop exhibits a vortex state at remanence. Analytical calculation of total free energy of both vortex as well as buckled state and the comparison thereof shows that the vortex state is ground state if radius of nanodisk is above 60 nm. Below this critical radius, buckled state is the ground state. But the non-appearance of vortex state at remanence in in-plane hysteresis loop of all of the nanodisks indicates a presence of energy barrier between vortex and buckled state. Height of the energy barrier is estimated using nudged elastic band method (NEBM) in all cases which proves that the energy barrier for vortex state weakens and the barrier for buckled state intensifies with the reduction of nanodisk size. At the critical radius of 60 nm , crossover of the two barrier heights occurs. Eventually, at the radius of 30 nm , the vortex state becomes totally unstable which can be toppled to buckled state with the slightest of perturbation. • In-plane hysteresis in convex nanodisk yields buckled state at remanence. • Remanent state is a vortex state for out-of-plane magnetization reversal. • Height of vortex to buckle state energy barrier decreases with radius. • Critical radius is 60 nm above which vortex is a stable state. [ABSTRACT FROM AUTHOR]

The magnetisation reversal in Ir x Mn 1 − x /CoFe exchange bias bilayers has been investigated as a function of the level of Ir content,' x ', in the stack where x = 0.15, 0.19 and 0.22. Values of the anisotropy constant of IrMn in excess of 10 7 erg/cc were obtained for the samples with a lower Ir content. Increasing the Ir content to 22% decreases the value of the anisotropy by ∼ 40% which results in a significant reduction in the thermal stability of the samples. While a higher thermal stability is desired for high temperature applications, the stronger anisotropy observed for the x = 0.15 samples results in an increased shearing of the hysteresis loops and, as a consequence, a much wider switching field distribution. Hence, in practice, approaches that combine the high anisotropy of low Ir content with the narrower switching field distribution observed in systems with high levels of Ir might be required. • Ir content ¿20% leads to a sharp reversal, i.e. narrow switching field distribution. • Low Ir content improves thermal stability but significant loop shearing is observed. • This has implications for devices that operate over a broad magnetic field range. • A strategy for improved shearing while maintaining thermal stability is presented. [ABSTRACT FROM AUTHOR]

• A strategy to realize nonvolatile magnetization reversal is proposed based on electric field control of interlayer coupling. • The dependence of interlayer coupling energy on electric field strength follows a continuous odd function in mathematics, guaranteeing the nonvolatility. • The feasibility of this strategy is demonstrated by a MnBi 2 Te 4 / h -BN/Fe 3 GaTe 2 / h -BN/MnBi 2 Te 4 junction. Achieving electric field control of nonvolatile magnetization reversal in van der Waals magnetic tunnel junctions (vdW MTJs) is of paramount importance for nanoscale spintronic devices with ultralow-power consumption and high-density storage. Here, a new and universal design strategy is proposed to realize nonvolatile magnetization reversal, which is based on electric field control of interlayer coupling. The nonvolatility benefits from the proposed special principle of vdW MTJ, in which the dependence of interlayer coupling energy on electric field strength follows a continuous odd function in mathematics. The feasibility of proposed strategy is proved by the MnBi 2 Te 4 / h -BN/Fe 3 GaTe 2 / h -BN/MnBi 2 Te 4 junction. The magnetization state of Fe 3 GaTe 2 can be reversed 180° by changing electric field directions. Moreover, the magnetization states can be preserved after removing electric field, demonstrating the nonvolatile magnetization reversal. Therefore, the present strategy provides an alternative approach to realize electric control of nonvolatile magnetization reversal in vdW MTJs for next-generation spintronic devices. [ABSTRACT FROM AUTHOR]

Magnetic viscosity analysis is a widely studied topic in understanding the stability and magnetization mechanisms of magnets. However, observing the minute changes in magnetic domains during the magnetic viscosity process poses a challenge in research. To address this issue, a self-made in-situ magnetized sample holder was used in this study to observe the dynamic evolution of domain structures in alnico alloy during magnetic viscosity. The findings indicate that the domain reversal during magnetic viscosity is largely irreversible, with only minor reversible changes observed in the inhomogeneous region. The magnetization reversal in alnico alloy occurs through the reversal of α1 phases, which follows a single domain particle reversal mode. The zero-field activation energy (E 0) of alnico alloy is determined as 3.30 × 10−17 J, and the coercivity field without thermal disturbance (H 0) is measured at 1779.19 Oe. This research method proves to be a valuable tool in the study of magnetic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent years, the research focus has shifted towards the preparation of non-heavy rare earth (RE)-Fe-B magnets with high coercivity (H cj) by reducing the content of B element. In this work, we achieved resource-saving sintered (Nd, Ce)-Fe-B magnets by adjusting the B element content, optimizing microstructure, and enhancement of Nd/Ce element distribution. We conducted an analysis on the magnetic characteristics, phase composition, microstructure, magnetization reversal mechanism, and economic viability of these sintered magnets. With a decrease in the B element content from 0.96 wt% to 0.90 wt%, there is a increase of approximately 1 kOe in H cj.At the same time, the temperature coefficient of H cj has been improved, resulting in a absolute value decrease from 0.67%/°C to 0.63%/°C. The findings suggested that reducing the mass fraction of B element could facilitate the formation of a thicker grain boundary phase between the grains. It could significantly weaken the ferromagnetic coupling effect, and enhance the magnetic isolation effect between grains, resulting in a higher H cj. From an economic perspective, compared to the cost of magnet with similar coercivity prepared by increasing the RE content, the cost of magnet with low B element content was reduced by 554.4 US$/t , approximately saving 3.08%. This study provides a new theoretical foundation and experimental basis for resource-saving sintered (Nd,Ce)-Fe-B magnet preparation. • By reducing 0.06 wt% B content, the coercivity of the magnet increases by 1 kOe. • Enhanced the coercivity temperature stability of the magnet. • Preparing similar coercivity magnets can save 3.08% of the cost, approximately 4008.4 RMB/t. • Clarified the mechanism of B's influence on coercivity. • It is of great significance for the preparation of resource-saving magnets. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanowires with radius varying nonlinearly along its length on z axis is considered. • The radius is proportional to z δ where δ is degree of nonlinear modulation. • If δ < 1 2 , magnetization reversal proceeds by pinning of vortex domain wall. • When δ ≥ 1 2 , magnetization reversal proceeds by motion of vortex domain wall. • Nonlinear modulation paves a way to control domain wall movement. Micromagnetic simulation of magnetization reversal is studied on cylindrical tapered nanowire with radii 50 nm and 10 nm at wider and narrower end respectively. The radius decreases from wider end to the narrower end non-linearly as R - β z δ where δ is the degree of non-linearity. Value of δ is either an integer (n) or reciprocal of integer (1 / n). At remanence, a vortex and flower state at the wider and narrower extremes respectively are exhibited combined with ferromagnetic ordering in the majority of volume. When δ is below 1 / 2 , pinning and depinning of domain wall drives the hysteresis following a Modified Kondorsky model. Otherwise, the magnetization reversal proceeds with nucleation and propagation of vortex domain wall according to Kondorsky model. The propagation of domain wall is dependent upon the value of δ which suggests tunability of magnetic characteristics with modulation of diameter. For instance, large values of coercivity is observed for wires that have strong domain wall pinning which is considerably reduced when depinning and propagation of domain wall takes over. A large range (20 kA / m to 130 kA / m) of coercivity can be obtained by changing the modulation. [ABSTRACT FROM AUTHOR]

We explore epitaxial growth of Co 2 MnSi/Ge/Co 2 MnSi vertical spin-valve structures on Si, where the Co 2 MnSi (CMS) is expected to be a half-metallic material for spintronics. By combining solid phase epitaxy, low-temperature molecular beam epitaxy, and atomic layer termination techniques, we can grow an epitaxial Ge layer on CMS at 250 °C, where the atomic interdiffusion between Ge and CMS is suppressed. After further optimization of the growth condition of the Ge intermediate layer, all-epitaxial CMS/Ge/CMS vertically stacked structures with spin-valve like magnetization reversal processes are demonstrated. This vertically stacked structures can be utilized for vertical spin-valve devices with a Ge channel on Si. [ABSTRACT FROM AUTHOR]

The grain boundary diffusion (GBD) technology effectively utilizes heavy rare earth (HRE) elements to improve the coercivity of sintered Nd-Fe-B magnet. Significantly, clarifying its coercivity improvement mechanism is essential for further optimizing the process and performance. Through comparative analysis with commercial conventional magnets (CSH) processing equivalent coercivity, this study investigated the specific mechanism by which the GBD method enhances the coercivity of HRE elements in an efficient manner. To achieve the same coercivity (∼21.4 kOe), GBD magnets contained only 0.25 wt% Tb, whereas CSH magnets had 1.17 wt% Dy and 1.18 wt% Tb. The microstructure analysis revealed that the Tb element in the GBD magnet was concentrated in the outer layer of the grain, constituting 17.37 wt% of the total rare earth content. While, in CSH magnets, the HRE element in the main phase grains accounted for only 9.58 wt % of the total rare earth elements, including Dy (3.83 wt %) and Tb (5.75 wt %). The characteristic core-shell structural grains in GBD magnet also endowed it with an uneven magnetic domain structure and a more concentrated "abrupt" magnetization reversal. Based on the characterization results the nucleation positions of the two types of magnets were analyzed by fitting H ci / M s and H a / M s. The results can serve as a guide for enhancing coercivity in grain boundary diffusion sintered Nd-Fe-B magnets, aiding in process and property optimization, and advancing the understanding of nucleation type mechanisms. • Coercivity enhancement mechanism of grain boundary diffusion (GBD) NdFeB magnets by comparing with commercial magnets (CSH). • The GBD method saves heavy rare earth (HRE) resources compared to CSH. • The typical core-shell structural grains of GBD magnets can effectively improve the coercivity. • The nucleation positions of the CSH and GBD magnets were analyzed by fitting H ci / M s and H a / M s. [ABSTRACT FROM AUTHOR]

Although the magnetization reversal process in the permanent magnets has long been studied, it has not been fully revealed. The recent progress of the computational science realizes the atomistic calculations for the thermally activated magnetization reversal process in permanent magnets. In contrast, the experimental study on the magnetization reversal has remain to be the macroscopic evaluation. In this study, Nd-Fe-B hot-deformed magnets are micropatterned, and a staircase-like magnetization curve corresponding to the elemental domain-wall depinning event at each grain boundary is successfully observed. Each elemental domain-wall depinning event fluctuates with respect to thermal activation, and the stochastic analysis based on the Néel-Arrhenius model gives the energy barrier parameters H 0 and E 0 of each depinning event, which are the intrinsic domain-wall depinning field and energy barrier height, respectively. Three types of Nd-Fe-B hot-deformed magnets with different coercivities are adopted for this stochastic analysis. As a result, E 0 exhibits very little dependence on H 0 , and its slope becomes steeper for the lower-coercivity magnet. The stochastic micromagnetics simulation based on the Landau-Lifshitz-Gilbert equation for the two-grain model with various inter-grain exchange coupling reproduces the experimentally observed relationship between E 0 and H 0. Moreover, the behavior for the lower-coercivity magnet can be explained by assuming the presence of a low magnetic anisotropy layer on the grain surface. Micropatterned Nd-Fe-B hot-deformed magnet and the anomalous Hall effect signal for an elemental domain-wall depinning event. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Recently 1:12 magnets of Sm-(Fe,V) have shown promising coercivities and the potential to be alternative rare-earth-lean permanent magnets. In this work, we investigated the effects of partial substitution of Cu, Mo and Ti for V in the magnets prepared by hot compaction and hot deformation of mechanically milled powders. The microstructure of the Sm-Fe-(V,Cu) and Sm-Fe-(V,Ti) hot-deformed magnets consisted in fine grains with sizes between 50 and 150 nm. The Sm-Fe-(V,Cu) magnet showed the best performance with μ 0 H c = 0.96 T, μ 0 M r = 0.49 T, (BH) max = 42 kJ m − 3 and T C = 362 ∘ C. Atom probe tomography of this magnet revealed the presence of a thin Sm 17.5 Fe 71.5 V 8 Cu 3 intergranular phase of 3-6 nm surrounding the 1:12 nanograins. The addition of a small amount of Cu, not only improved the magnetic properties but also hindered the grain growth during hot deformation. Micromagnetic simulations of the magnetization reversal agreed with the experimental values of coercivity. The presence of the intergranular phase reduces the number of grains that switch simultaneously. [ABSTRACT FROM AUTHOR]

A sonochemical reactor was used to synthesize Mn 0.5 Cu 0.5 La x Fe 2− x O 4 (x = 0.025, 0.050, 0.075, and 0.100) nanoferrites. The structural, electrical, and magnetic properties were investigated for the samples using X-ray diffraction and vibrating sample magnetometer, and electrochemical impedance spectroscopy. The hysteresis analysis also reveals a unique soft ferromagnetic behavior for the studied nanoferrites. The doping of La3+ in Mn 0.5 Cu 0.5 La x Fe 2 -x O 4 increases the bandgap energy, dielectric constant and coercivity while the field of saturation magnetization decreases. Reflection loss measurement reveals that these ferrites could be used as radiation absorption material in the X-band and K u -band frequency. [ABSTRACT FROM AUTHOR]

Magnetization enhancement is observed in the bi-magnetic systems including paramagnetic (PM)/antiferromagnetic (AFM), AFM/AFM, and ferromagnetic (FM)/AFM composites systems, and attributed to the effects of oxidation states of metallic ions on the interface exchange-coupling. With respect to the FM/FM system, in this study, the enhanced magnetization in hard CoFe 2 O 4 (CFO)/soft La 0.7 Sr 0.3 MnO 3 (LSMO) composites with different mass ratios of LSMO (R s) was observed for the first time. The values of saturation magnetization (M s) of CFO and LSMO at 10 K were found to be 111 and 113 emu/g, respectively. For the CFO/LSMO composites, M s was below 111 emu/g for R s ≤ 15% because the antiferromagnetically coupled CFO/LSMO system maintains the super-spin glass (SSG) state with the moment of CFO particles being randomly oriented. However, M s increases to 133 and 127 emu/g for R s = 18 and 21%, respectively, because the higher content of LSMO separates the CFO particles and destroys the SSG state, thus enabling the moment of CFO particles to rotate easily and align with the external magnetic field. Mechanism for the magnetization enhancement reported herein is different from the interface exchange-coupling mechanism, which enriches the understanding of the magnetization reversal in bi-magnetic systems and provides the experimental reference for the applications of bi-magnetic materials. [ABSTRACT FROM AUTHOR]

Laser based powder bed fusion is a promising manufacturing method that can be used for the fabrication of hard magnets such as NdFeB with nearly any given geometrical shape. However, the weak performance, e.g., low coercivity, of the 3D-printed magnets currently hinder their application. In this work, we demonstrated a proof-of-concept of powder bed additive manufacturing of heavy rare earth free NdFeB magnets with technologically attractive coercivity values. The 3D-printed NdFeB magnets exhibit the highest (up-to-date for the additively manufactured magnets without heavy rare earth metals) coercivity values reaching μ 0 H c = 1.6 T. The magnets were synthesized using a mixture of the NdFeB-based and the low-melting eutectic alloy powders. The essential function of the eutectic alloy, along with binding of the NdFeB-based magnetic particles, is the significant improvement of their coercivity by the in-situ grain boundary (GB) infiltration. The fundamental understanding of the magnetization reversal processes in these 3D-printed magnets leads to the conclusion that the excellent performance of the additively manufactured hard magnets can be achieved through the delicate control of the intergrain exchange interaction between the grains of the Nd 2 Fe 14 B phase. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We studied the angular dependence and thermal stability of coercivity of Nd-rich Ga-doped Nd–Fe–B sintered magnets. Experimentally measured angular dependence of coercivity for the as-sintered magnet agrees well with the micromagnetic simulation results for exchange-coupled polycrystalline model that assumes the magnetization reversal is dominated by the domain wall depinning at the grain boundaries. On the other hand, the measured angular dependence of coercivity of the post-sinter annealed sample with an enhanced coercivity deviates from fully exchange-decoupled model in spite of previous experimental results on inter-grain exchange decoupling. Based on micromagnetic simulations and Kronmüller equation, it is suggested that the entire elimination of magnetic exchange coupling between Nd 2 Fe 14 B grains can further improve the coercivity and its thermal stability of the 5 µm-grain-sized Dy-free magnet. Image, graphical abstract [ABSTRACT FROM AUTHOR]