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The influence of size on the dynamic magnetic hysteresis properties and dynamic phase transitions of Fe and F e 3 O 4 2D-circular nanodisks with varying diameters has been explored in the micromagnetic framework. This investigation is conducted under a sinusoidal dynamic magnetic field along the x-direction by solving the Landau-Lifshitz-Gilbert (LLG) equation with the OOMMF software at zero temperature. The dynamic hysteresis of nanodisks is profoundly impacted by both the frequency and amplitude of the applied external field, along with the particle size. As particle size decreases, there is an observed increase in the frequency values at which the transition to dynamic ordered frequency occurs in Fe nanodisks, whereas a decrease is noted in the transition frequency values of F e 3 O 4 nanodisks. [ABSTRACT FROM AUTHOR]

MoO2-Fe2O3 nanoparticle systems were successfully synthesized by mechanochemical activation of MoO2 and α-Fe2O3 equimolar mixtures throughout 0–12 h of ball-milling. The role of the long-range ferromagnetism of MoO2 on a fraction of more defect hematite nanoparticles supporting a defect antiferromagnetic phase down to the lowest temperatures was investigated in this work. The structure and the size evolution of the nanoparticles were investigated by X-ray diffraction, whereas the magnetic properties were investigated by SQUID magnetometry. The local electronic structure and the specific phase evolution in the analyzed system versus the milling time were investigated by temperature-dependent Mössbauer spectroscopy. The substantially shifted magnetic hysteresis loops were interpreted in terms of the unidirectional anisotropy induced by pinning the long-range ferromagnetic order of the local net magnetic moments in the defect antiferromagnetic phase, as mediated by the diluted magnetic oxide phase of MoO2, to those less defect hematite nanoparticles supporting Morin transition. The specific evolutions of the exchange bias and of the coercive field versus temperature in the samples were interpreted in the frame of the specific phase evolution pointed out by Mössbauer spectroscopy. Depending on the milling time, a different fraction of defect hematite nanoparticles is formed. Less nanoparticles supporting the Morin transition are formed for samples exposed to a longer milling time, with a direct influence on the induced unidirectional anisotropy and related effects. [ABSTRACT FROM AUTHOR]

The effects of both magnetic field and temperature on the magnetic hysteresis of (Zn0.95Ni0.05O)x/(Cu0.25Tl0.75)Ba2Ca3Cu4O12 − δ, x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 wt.%, were studied. The magnetic parameters such as the lower "Hc1" and the upper "Hc2" critical magnetic fields, the zero temperature coherence length [ξ(0], the coercive field Hcoer., the remanent magnetization Mr, the vertical width Δ M, the magnetic critical current density Jc.mag, and the flux pinning density Fp were extracted from the analysis of the hysteresis loops. The experimental data of the Jc.mag were analyzed according to the power law, Kim model, and the exponential model. The results showed that the exponential model is more convenient in describing the obtained data than the power law and Kim models. In addition, with increasing the applied magnetic field, the samples containing nano-Zn0.95Ni0.05O were degraded less compared with the pure sample (Cu0.25Tl0.75)-1234. Thus, nano-Zn0.95Ni0.05O-addition to (Cu, Tl)-1234 had a significant effect on improving Jc.mag values. [ABSTRACT FROM AUTHOR]

Lanthanide permanent magnets are widely used in applications ranging from nanotechnology to industrial engineering. However, limited access to the rare earths and rising costs associated with their extraction are spurring interest in the development of lanthanide‐free hard magnets. Zero‐ and one‐dimensional magnetic materials are intriguing alternatives due to their low densities, structural and chemical versatility, and the typically mild, bottom‐up nature of their synthesis. Here, we present two one‐dimensional cobalt(II) systems Co(hfac)2(R‐NapNIT) (R‐NapNIT=2‐(2′‐(R‐)naphthyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide, R=MeO or EtO) supported by air‐stable nitronyl nitroxide radicals. These compounds are single‐chain magnets and exhibit wide, square magnetic hysteresis below 14 K, with giant coercive fields up to 65 or 102 kOe measured using static or pulsed high magnetic fields, respectively. Magnetic, spectroscopic, and computational studies suggest that the record coercivities derive not from three‐dimensional ordering but from the interaction of adjacent chains that compose alternating magnetic sublattices generated by crystallographic symmetry. [ABSTRACT FROM AUTHOR]

The magnetic properties of steels are affected by plastic deformation, because the domain wall processes magnetoelastically interact with the dislocations and the residual stresses. The evolution of the magnetic hysteresis loop and its parameters with the type and degree of straining can thus provide a macroscopic signature of the underlying the mechanical and structural properties. Additional information can be achieved at a microscopic level through analysis of the Barkhausen noise, the signal generated by the stochastic flux variations associated with the discontinuous motion of the domain walls. Nondestructive methods for the structural evaluation of magnetic steels, devoted, in particular, to the investigation of work-hardening and state of internal stress following plastic straining, have therefore been developed in the literature, either through magnetic hysteresis or Barkhausen noise measurements. In this paper, we summarize significant results regarding the relationship between magnetic properties and plastic deformation in steel samples and the related experimental methods. Attention will be devoted, in particular, to the measurement and analysis of the Barkhausen noise spectral density and the way it relates to the macroscopic magnetic behavior and the structural properties. [ABSTRACT FROM AUTHOR]

Dynamic magnetic hysteresis (DMH) behaviors of the mixed spin-3/2 and spin-2 Ising bilayer system with different crystal-field interactions on a two-layer square lattice is studied by the use of dynamic mean field calculations based on the Glauber-type stochastic. The hysteresis loops are obtained for different reduced temperatures ( T), magnetic field amplitudes ( h), frequencies ( w) and interlayer coupling constants ( J ). Influences of the T, h, w and J on the DMH properties are investigated. We also study the temperature, frequency and interlayer coupling interaction dependence of the coercive field and remanent magnetization. We compare our results with some theoretical and experimental works and observe a quantitatively good agreement with some theoretical and experimental results. [ABSTRACT FROM AUTHOR]

• Twin-crystal structures of fcc Ni (1 1 1) revealed in epitaxial Ni ultrathin films grown on c-cut sapphire Al 2 O 3 (0 0 0 1) substrates. • Enhanced Curie temperature as compared to bulk sample measured using temperature dependent MOKE. • MOKE and magnetization revealed uniaxial perpendicular magnetocrystalline anisotropy. • Correlation of surface and volume magnetization from MOKE and magnetic hysteresis. We report on the enhanced Curie temperature and magnetic anisotropy observed in the temperature dependence of magneto-optic Kerr effect (MOKE) in epitaxial Ni films grown on single-crystal c-cut sapphire Al 2 O 3 (0 0 0 1) substrates. X-ray diffraction (XRD) revealed the epitaxial growth of Ni (1 1 1) on Al 2 O 3 (0 0 0 1) substrate while XRD azimuthal scans indicated the presence of 60°-rotated twin-crystal structures of fcc Ni in ABC ...and ACB ... stacking in the Ni/Al 2 O 3 (0 0 0 1) film. Twin-crystal structures were also revealed from the surface morphology of the Ni (1 1 1) layer in the Ni/Al 2 O 3 (0 0 0 1) film. MOKE hysteresis loops indicated higher Kerr remanence with lower coercivity for the Ni/Al 2 O 3 (0 0 0 1) film as compared to the polycrystalline Ni film grown on Si (1 0 0) substrate under the same conditions. Azimuthal MOKE hysteresis loops confirmed the presence of 2-fold in-plane magnetic anisotropy in the Ni/Al 2 O 3 (0 0 0 1) film. Temperature dependent MOKE measurements in the range of 300– 680 K revealed a power-law dependence of the Kerr remanence similar to magnetization. The Curie temperature (T C) of the Ni/Al 2 O 3 film was found to be almost 10 K higher than bulk Ni. In- and out-of-plane magnetization revealed a uniaxial perpendicular magnetic anisotropy with the easy axis along the Ni/Al 2 O 3 film plane. The calculated values of the anisotropy constants revealed a high degree of magnetocrystalline anisotropy in the epitaxial Ni/Al 2 O 3 (0 0 0 1) film. A close correlation of MOKE and magnetization hysteresis loops indicated similar surface and volume magnetic behaviors in the thin films. The enhanced temperature dependent MOKE, magnetocrystalline anisotropy and magnetization could be attributed to the twin-crystal structures in the epitaxial Ni/Al 2 O 3 film. [ABSTRACT FROM AUTHOR]

We have observed an unusual type of positive exchange bias (EB) in polycrystalline Ni 3 Al–NiO core-shell nanoparticle system in that the M–H loop center shifts in the same direction as that of the cooling magnetic field, H cool , regardless of the sign and magnitude of H cool . However, for weak (≲ 50 Oe) negative cooling fields, as the temperature is raised, a crossover from positive to negative EB occurs at a temperature, which depends on the cooling temperature and H cool . This kind of positive EB is not accompanied by the training effect but by the vertical shift in the hysteresis loops, M E . A simple model of single-domain ferromagnetic particles embedded in a disordered antiferromagnetic matrix is shown to provide a straightforward explanation for the direct relation observed between the EB field, H E , and − M E . [ABSTRACT FROM AUTHOR]

The magnetic properties of antiferromagnetic CoO compound have been studied using Monte Carlo simulations within the Ising model framework. The thermal magnetizations and magnetic susceptibilities are computed for a fixed size. In addition, the Néel temperature is deduced. The magnetization versus the reduced exchange interactions and crystal field are studied for a fixed system size, N = 10 nm particles. The magnetic hysteresis cycle versus temperature is also established. [ABSTRACT FROM AUTHOR]

The phase diagrams and magnetic hysteresis behavior of a spin- 1 2 Ising core/shell nanoparticle are investigated by the use of the effective field theory with a probability distribution technique that accounts for the self-spin correlation functions. Nearest-neighbor pair interactions are incorporated between the Ising spins in the three parts of the nanoparticle that are core, core/shell and surface shell. The effects of the external magnetic field and core/shell exchange interaction on the thermal magnetization and susceptibility of the system are examined. [ABSTRACT FROM AUTHOR]

The random-anisotropy Heisenberg model is numerically studied on lattices containing over ten million spins. The study is focused on hysteresis and metastability due to topological defects, and is relevant to magnetic properties of amorphous and sintered magnets. We are interested in the limit when ferromagnetic correlations extend beyond the size of the grain inside which the magnetic anisotropy axes are correlated. In that limit the coercive field computed numerically roughly scales as the fourth power of the random anisotropy strength and as the sixth power of the grain size. Theoretical arguments are presented that provide an explanation of numerical results. Our findings should be helpful for designing amorphous and nanosintered materials with desired magnetic properties. [ABSTRACT FROM AUTHOR]

The magnetic properties of antiferromagnetic HoRh nanomaterials have been studied using Monte Carlo simulations within the Ising model framework. The considered Hamiltonian includes the first nearest neighbor, second and third exchange interactions, and an external magnetic field. The thermal magnetizations and magnetic susceptibilities are computed for a fixed size of the nanomaterial. In addition, the Néel temperature is deduced. The magnetization and magnetic susceptibility versus the exchange interactions are studied for a fixed size of the nanomaterial. The magnetic hysteresis cycle versus temperature is also established. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic properties of antiferromagnetic GdSb layers have been studied using Monte Carlo simulations within the Ising model framework. The considered Hamiltonian includes first nearest-neighbor, an external magnetic field and a crystal field. The thermal magnetizations and magnetic susceptibilities are computed for a fixed size. In addition, the Néel temperature is deduced. The magnetization versus the exchange interactions and crystal field are studied for a fixed system size, N=5, 7 and 9 sites. The magnetic hysteresis cycle versus temperature is also established. [Copyright &y& Elsevier]

By means of vibrating-sample-magnetometry measurements and micromagnetic simulations, we investigated the hysteresis loops of electrodeposited NiFe/Cu multilayered nanowires arrays. There is a detailed comparison between the hysteresis loops of arrays of multilayered nanowires and three-dimensional micromagnetic simulations. Two different structures are studied and compared: (a) conventional multilayered NiFe/Cu nanowires and (b) NiFe/Cu/NiFe trilayers magnetically isolated by a thick Cu layer. The nanowires are fabricated by electrodeposition in the pores of anodic aluminum oxide templates with diameters as small as 35 nm. Micromagnetic simulations are in good agreement with the experimental results, giving us a better insight on the influence of the shape anisotropy, the inter-wire, and the intra-wire magnetostatic coupling on the characteristic parameters of the hysteresis loop of multilayered nanowires arrays. Furthermore, micromagnetic simulations showed that for multilayered nanowires coercivity, values increased rapidly as the number of the ferromagnetic layers for a single nanowire increased up to the number of four layers, whereas coercivity decreased when the number of nanowires composing an array increased. [ABSTRACT FROM PUBLISHER]

Physical vapor deposition prepared FeCoB(100 nm)/Al2O3/FeCoB(100 nm) sandwich structures with different Al2O3 thickness (2 to 15 nm) were studied. The magnetization curves showed that the in-plane coercive field and saturation field along the easy axis decreased with increase in Al2O3 thickness. The saturation magnetization field 4 \piM s for all samples is above 1.6 T. The coercive field remained below 0.5 Oe for Al2O3 thickness greater than 6 nm, approximately when the antiferromagnetic coupling switched to ferromagnetic coupling. The existence of optical modes in ferromagnetic resonance (FMR) curves confirmed antiferromagnetic coupling in samples with Al2O3 thickness below 6 nm. At 8.5 GHz, the sandwich structure with a 3 nm Al2O3 layer displayed a narrow linewidth of only 29 Oe, indicating lower magnetic loss in the sandwich structure compared to the single layer FeCoB with a thickness of 200 nm that exhibited a linewidth of 50 Oe. Also, all sandwich structures demonstrated real relative permeability of above 600 up to 1.5 GHz. The FeCoB(100 nm)/Al2O3(3 nm)/FeCoB(100 nm) structure with low coercive field, high magnetization, and low FMR linewidth presents great potential in RF magnetic application. [ABSTRACT FROM AUTHOR]

Variable-field magnetic force microscope (MFM) is introduced to characterize the magnetic behavior of commercially available MFM probes that is relevant to interpret MFM imaging. A Nanotec Electronica S.L. microscope has been conveniently modified to apply magnetic fields in axial direction (up to 1.5 kOe) and in-plane direction (up to 2.0 kOe). Axial and transeverse hysteresis loops of the probes have been generated by measuring the changes in the MFM contrast observed when the magnetic field is applied. The variation of the MFM signal is ascribed to the modification of the magnetic state of the tips. This is enabled by the large coercitivity (~1.7 kOe) of the checked longitudinal recording media. The properties of the probes depend on the coating material, the macroscopic tip shape, and tip radius. In only a few cases, the magnetization of the probe can be oriented along in-plane orientation. In addition, the stray field of the tips has been deduced by measuring the influence of the probe in the magnetic state of the checked samples. [ABSTRACT FROM PUBLISHER]

Thermomagnetics of a system of interacting particles with log normal distribution of particle size and anisotropy constant was studied self-consistently using a Monte Carlo calculation within the mean-field approximation. Characteristic hysteretic behavior and reversible transverse susceptibility (RTS) were investigated. The salient features are as follows: The hysteresis loops become sheared with increasing anisotropy distribution, /spl sigma//sub K/, while their slopes steepen with the mean field strength /spl alpha/. For a homogeneous systems RTS peaks increase sharply with /spl alpha/, both at the anisotropy field H/sub K/ and coercive field H/sub c/. For random systems, both peaks become shallower and blunted with increasing /spl sigma//sub K/. Mean field strength /spl alpha/ causes the peak positions of RTS at H/sub K/ to shift to lower values, while the shift at H/sub c/ depends subtly upon the interplay among /spl alpha/, /spl sigma//sub K/ and texture of the system. For random systems the shift is toward higher H/sub c/ values with increasing /spl alpha/. For systems with constant /spl alpha/, however, it shifts toward lower values with increasing /spl sigma//sub K/. [ABSTRACT FROM PUBLISHER]

Abstract: The hydrogenation effect on the hysteresis properties of rapidly quenched (RQ) (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2 compound obtained by melt-spinning is studied. A comparative study of RQ alloy and its hydride (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2H2.5 has shown that hydrogenation resulted in the increase of magnetization without significant effect on the Curie temperature. In contrast to hydrogen-free alloy having a maximum on the H c(T) curve, the H c of the hydrogen-charged compound increased monotonously with decreasing temperature. Among the factors affecting H c in hydrogenated sample are the increase of the grain size of the crystalline phase and the decrease of both the iron and the rare earth contributions to the magnetocrystalline anisotropy. High-field hysteretic distortions of the magnetization/demagnetization curves of RQ and RQ+hydrogen samples are observed at 4.2K in fields up to 90kOe indicating the existence of a magnetic phase with very high local coercivity. [Copyright &y& Elsevier]