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The surface, size and ion doping effects on the magnetic, phonon and optical properties of ZnS nanoparticles are studied based on the s-d model including spin-phonon and Coulomb interaction, and using a Green's function theory. The changes of the properties are explained on a microscopic level, due to the different radii between the doping and host ions, which cause different strains—compressive or tensile, and change the exchange interaction constants in our model. The magnetization increases with increasing small transition metal (TM) and rare earth (RE) doping concentration. For larger TM dopants the magnetization decreases. The phonon energies increase with increasing TM, whereas they decrease by RE ions. The phonon damping increases for all doping ions. The changes of the band gap energy with different ion doping concentration is also studied. Band gap changes in doped semiconductors could be due as a result of exchange, s-d, Coulomb and electron-phonon interactions. We have tried to clarify the discrepancies which are reported in the literature in the magnetization and the band gap energy. [ABSTRACT FROM AUTHOR]

The datasets presented in this article are related to materials research on hard ferromagnet in TM-Fe-Si (TM=Ti, Zr, Hf, V, Nb, and Ta) ternary systems. The motivation for data collection is based on the research paper entitled “Novel hard magnetic phase with Zr11.5Fe53Si35.5 composition”. The datasets are composed of scanning electron microscope images, X-ray diffraction (XRD) patterns, and magnetization data for TM7Fe52Si41 annealed at 1050 °C. The chemical compositions of constituent phases were determined by an energy dispersive X-ray spectrometer (EDS). The phase analysis was performed using XRD and EDS results. The Curie temperature of each sample was obtained using magnetization data, and the coercive field was determined for hard ferromagnet samples Zr7Fe52Si41 and Hf7Fe52Si41. The datasets would be useful for developing an Fe-based rare-earth-free permanent magnet, which is one of the central issues of materials science.

Improving the performance of electrical steels within the magnetic circuits is essential to save energy. The domain refinement through local surface treatment by laser is an effective technique to reduce the iron losses in grain-oriented iron silicon steels. To interpret the mechanism of this technique, we have quantitatively studied the impact of nanosecond pulse laser treatment on the magnetic properties of grain-oriented Fe(3%wt)Si sheets. We measured the total power loss and apparent permeability of the samples using a Single-Sheet Tester (SST). The laser treatment resulted in a loss reduction of up to 24% compared to the average power loss of standard samples at 50 Hz. At mid-induction levels, the reduction was also accompanied by an improvement in apparent permeability. A dynamic magnetic behavior law was used to identify a dynamic property A including information on density, surface area and wall mobility and another internal permeability property Λ representative of static field and magnetization characteristics. Lastly, we presented the behavior of these properties under different laser treatment. [ABSTRACT FROM AUTHOR]

The surface, size and ion doping effects on the magnetic, phonon and optical properties of ZnS nanoparticles are studied based on the s-d model including spin-phonon and Coulomb interaction, and using a Green’s function theory. The changes of the properties are explained on a microscopic level, due to the different radii between the doping and host ions, which cause different strains—compressive or tensile, and change the exchange interaction constants in our model. The magnetization increases with increasing small transition metal (TM) and rare earth (RE) doping concentration. For larger TM dopants the magnetization decreases. The phonon energies increase with increasing TM, whereas they decrease by RE ions. The phonon damping increases for all doping ions. The changes of the band gap energy with different ion doping concentration is also studied. Band gap changes in doped semiconductors could be due as a result of exchange, s-d, Coulomb and electron-phonon interactions. We have tried to clarify the discrepancies which are reported in the literature in the magnetization and the band gap energy.

Square magnetic nanodots can show intentional or undesired shape modifications, resulting in superellipses with concave or convex edges. Some research groups also concentrated on experimentally investigating or simulating concave nano-superellipses, sometimes called magnetic astroids due to their similarity to the mathematical shape of an astroid. Due to the strong impact of shape anisotropy in nanostructures, the magnetization-reversal process including coercive and reversibility fields can be expected to be different in concave or convex superellipses than that in common squares. Here, we present angle-dependent micromagnetic simulations on magnetic nanodots with the shape of concave superellipses. While magnetization reversal occurs via meander states, horseshoe states or the 180° rotation of magnetization for the perfect square, depending on the angle of the external magnetic field, more complicated states occur for superellipses with strong con-caveness. Even apparently asymmetric hysteresis loops can be found along the hard magnetization directions, which can be attributed to measuring minor loops since the reversibility fields become much larger than the coercive fields. [ABSTRACT FROM AUTHOR]

Using the first principle calculations, we investigated the temperature-dependent magnetic properties of Bi-doped Fe16N2. We found that the Bi doping resulted in the lattice expansion and consequently the volume expansion occurred. Due to this volume expansion, the saturation magnetization of Bi-doped system was suppressed by 12% compared with that of pure Fe16N2. Nonetheless, the hybridization effect between Fe 3d and Bi 6p orbitals contributed to enhancing the magnetocrystalline anisotropy from 0.73 meV/cell in pure Fe16N2 to 1.57 meV/cell in Bi-doped system. Through the temperature-dependent magnetization dynamics, we found that the Bi-doped system had a coercive field of 9.63 kOe at 300 K while the pure Fe16N2 alloy had a coercive field of 3.61 kOe. Furthermore, a maximum energy product of 70.2 MGOe at 300 K was found in Bi-doped system. Overall, we propose that the Bi-doped system can be a potential rare-earth-free permanent magnet (PM). [ABSTRACT FROM AUTHOR]

Abstract: The magnetic properties of polycrystalline and amorphous cobalt- and nickel-ferrite films obtained by solid-phase synthesis are studied. Polycrystalline nickel-ferrite films are shown to be characterized by significant coercive fields at room temperature in the direction normal to the substrate plane. Compressive stresses that arise in the films during solid-phase oxidation and synthesis are assumed to contribute to the enhancement of the coercive fields. In polycrystalline films, a magnetic anisotropy of the "easy plane" type, characteristic of two-dimensional layers, is found. X-ray amorphous films have only paramagnetic properties. [ABSTRACT FROM AUTHOR]

The magnetic properties of Ni50Mn36Sn14 Heusler alloy with L21 structure (L21-NiMnSn HA) are investigated by using the Kaneyoshi approach (KA) within the effective field theory. Mn atoms have two different magnetic properties, and Sn atoms also have two different magnetic properties, according to the lattice location. The L21-NiMnSn HA and its components (Mn1, Mn2, Sn1, Sn2, and Ni) exhibit a second-order phase transition from the ferromagnetic phase to the paramagnetic phase at TC = 2.824. The magnetizations of the HA are obtained as Sn2 > Ni > Mn2 > L21-NiMnSn HA > Sn1 > Mn1 at T < TC. We suggest that the magnetizations of the HA decrease from that of its core atom to its corner atoms. We refer to the different magnetization behavior of the Mn atoms and the Sn atoms of the HA as “lattice location effect (LLE)” because the magnetic difference of the Mn atoms and the Sn atoms of the HA results from their lattice location on the L21 structure. While the coercive fields are the same with each other, their remanence magnetizations are different. Our theoretical results of M(T) and M(H) of L21-NiMnSn HA are in quantitatively good agreement with some experimental results of NiMnSn alloys. Furthermore, the magnetization critical exponent is obtained. Its value is in good agreement with some experimental results and the mean field theory. This case indicates that the model exhibits a universal critical behavior. [ABSTRACT FROM AUTHOR]

Cobalt ferrite magnetic nanoparticles (CoFe2O4-MNPs) were synthesized by hydrothermal and co-precipitation methods using different precursors such as nitrates, chlorides, and acetates, at different concentrations with/without surfactant under different growth conditions. The structural and morphological analyses reveal the formation of a single-phase CoFe2O4 in nanoplatelet-shaped NPs with average particle size between 11 and 26 nm depending on synthesis condition. The specific surface area of these NPs obtained by hydrothermal method was ~ 34 m2 g−1. Electrochemical performances of the obtained nanoparticles in a three-electrode configuration with a 6 M KOH electrolyte revealed a specific capacitance (Cs) of 429 F/g at 0.5 A/g, with excellent capacitance retention of 98.8% after 6000 cycles at 10 A/g for the electro-active NPs synthesized by hydrothermal method at 200 °C for 18 h. [ABSTRACT FROM AUTHOR]

Coercive fields of piezoelectric materials can be strongly influenced by environmental temperature. We investigate this influence using a heterostructure consisting of a single crystal piezoelectric film and a quantum dots containing membrane. Applying electric field leads to a physical deformation of the piezoelectric film, thereby inducing strain in the quantum dots and thus modifying their optical properties. The wavelength of the quantum dot emission shows butterfly-like loops, from which the coercive fields are directly derived. The results suggest that coercive fields at cryogenic temperatures are strongly increased, yielding values several tens of times larger than those at room temperature. We adapt a theoretical model to fit the measured data with very high agreement. Our work provides an efficient framework for predicting the properties of ferroelectric materials and advocating their practical applications, especially at low temperatures. [ABSTRACT FROM AUTHOR]

The effect of surface shell parameters on the hysteresis loop behaviors of a decorated Ising cubic nanotube, consisting of a ferromagnetic spin- 1 2 core which is interacting ferrimagnetically with a ferromagnetic spin-1 surface shell, is investigated, in the present work, within the effective-field theory with correlations based on the probability distribution technique. We have found that these parameters have a strong effect on the shape and the number of hysteresis loops and also on the coercive field and remanent magnetization behaviors. Indeed, triple, quintuple, septuple and nonuple hysteresis loop patterns have also been observed. [ABSTRACT FROM AUTHOR]

In this study, the effects of next-nearest neighbor interaction on a one-dimensional mixed spin 3 - spin 3/2 Ising model was investigated using Cellular Automaton (CA). The Ising model hamiltonian contains the antiferromagnetic nearest neighbor interaction (J 1 ), the ferromagnetic next- nearest neighbor interaction (J 2 ) and the external magnetic field (h = H/J 1 ). Magnetization (M) of the mixed spin system was obtained in the interval 0 ≤ R ≤ 1 of the interaction ratio (R = J 2 /J 1 ) using field cooling (FC) and zero-field cooling (ZFC) processes. Hysteresis curves were drawn for several R values in the interval −0.1 ≤ h ≤ 0.1 using FC results. The functional behavior for coercive field (H C ) was determined depending on R. Thus, the mixed spin system became a hard magnetic material and the lattice geometry also changed from one dimensional linear chain to triangular chain with increasing R value. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the anisotropy in the exchange interaction on the hysteresis loops within the anisotropic quantum Heisenberg model has been investigated with the effective field theory for two spin cluster. Particular attention has been devoted on the behavior of the hysteresis loop area, coercive field and remanent magnetization with the anisotropy in the exchange interaction for both ferromagnetic and paramagnetic phases. [Copyright &y& Elsevier]

Abstract: The transition metal sulfide Fe4Ti3S8 with 7:8 composition has been synthesized and studied by using X-ray diffraction, magnetization and electrical resistivity measurements. This compound exhibits a monoclinic crystal lattice (space group I12/m1). The substitution of Ti for Fe in Fe7S8 is found to result in a lowering of the Curie temperature (T C ≈ 205 K), in a larger value of the coercive field (H c ∼ 9 kOe at low temperatures) and in a substantial growth of the resultant magnetic moment per formula unit (μ FU) in comparison with Fe7S8. An enhanced value of μ FU is attributed to the preferential substitution of Ti in alternating cation layers. From the paramagnetic susceptibility measured within temperature interval (250–350) K, a reduced value of the effective moment per iron (μ Fe ∼ 2.4μ B) was determined. The electrical resistivity of Fe4Ti3S8 shows a non-metallic behavior and is affected by magnetic ordering. [Copyright &y& Elsevier]

Magnetic properties of composites prepared by coating lacquer containing neodymium iron boron (Nd-Fe-B) powders on rubberwood were characterized by vibrating sample magnetometry (VSM), magnetic moment measurements, and attraction tests with an iron-core solenoid. The Nd-Fe-B powders were recycled from electronic wastes by the ball-milling technique. Varying the milling time from 20 to 300 min, the magnetic squareness and the coercive field of the Nd-Fe-B powders were at the minimum when the powders were milled for 130 min. It followed that the coercive field of the magnetic wood composites was increased with the milling time increasing from 130 to 300 min. For the magnetic wood composites using Nd-Fe-B obtained from the same milling time, the magnetic squareness and the coercive field were rather insensitive to the variation of Nd-Fe-B concentration in coating lacquer from 0.43 to 1.00 g/cm. By contrast, the magnetization and magnetic moment were increased with the Nd-Fe-B concentration increasing. Furthermore, the electrical current in the solenoid required for the attraction of the magnetic wood composites was exponentially reduced with the increase in the amount of Nd-Fe-B used in the coating. [ABSTRACT FROM AUTHOR]

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]

Abstract: We demonstrate the magnetization reversal in magnetic tunnel junction (MTJ) spin-valves (SV) based on thin films and nanowires. We show the change of coercive force and magnetization direction of the soft magnetic layer at transition from a continuous film to a laterally confined nanostructure formed by focused ion beam technique. We discuss the possible mechanisms of coercivity and magnetic anisotropy transformations in nanowire spin-valves. Micromagnetic simulation of spin configuration gives the stripe domain structure in the soft layer of the nanowires, which defines magnetization reversal mechanism via domain wall displacement. SVs based on the continuous thin film have tunnel magnetoresistance (TMR) ratio about 20%, which is suitable for emerging nanoelectronic applications. [Copyright &y& Elsevier]

The effect of the shape anisotropy and dipolar interactions between NiFe magnetic layers on the magnetization reversal of NiFe/Cu multilayered nanowire arrays electrodeposited into the nanopores of anodic aluminum oxide (AAO) templates with diameters of 35 nm has been studied. The magnetization reversal mechanism has been investigated from the magnetic hysteresis loops of NiFe/Cu nanowires, for various angles \theta between the applied field and the nanowires axis. The magnetization reversal strongly depends on the variation of the aspect ratio (thickness/diameter) between NiFe and Cu layers. Based on the Aharoni's model and the Stoner-Wohlfarth model, we calculated the coercive field (Hc) of multilayered nanowires, considering also the intra-nanowires interaction. The calculated results are in good agreement with the experimental ones even for thin NiFe layers, when the calculated results without considering the magnetostatic coupling between the adjacent ferromagnetic layers are unable to follow the experimental results. Additionally, the angular variation of the normalized remanence (Mr(\theta)/Ms) for NiFe/Cu nanowires with various NiFe layers thickness was studied. The experimental Hc and Mr(\theta)/Ms values were derived from the hysteresis loops. [ABSTRACT FROM PUBLISHER]

Abstract: We report on the magnetization, magnetocaloric effect, magnetic ordering temperatures, saturation magnetic moments and anisotropy of sputter-deposited Gd x Cr1−x alloys with Gd atomic concentrations, x, ranging from 0.13 to 0.52. The complex magnetic nature of the Gd–Cr films was revealed from the M×H isotherms, which do not show saturation even at an applied field of 70kOe and a temperature of 2K and do not exhibit a linear behavior at higher temperatures. For some of the samples, the isotherms were used to determine the isothermal entropy variation as a function of temperature, for a change of 50kOe in the applied magnetic field. The saturation magnetic moment varies with x and follows the dilution law, implying that the Cr atoms do not contribute to the total moment of the Gd–Cr alloys. Both static magnetization and dynamic susceptibility measurements reveal the existence of a magnetic glassy behavior in the alloys, which occurs below a freezing temperature. The existence of anisotropy at low temperatures for all samples was revealed by their M×H hysteresis loops from which the in-plane coercive fields, H c , were determined. A monotonical increase in H c with increasing Gd concentration was observed. [Copyright &y& Elsevier]

Abstract: Barium hexaferrite samples BaFe12−2x Ti x Ru x O19 were prepared by ball milling and their structural and magnetic properties were investigated using X-ray diffraction, TEM, Mössbauer spectroscopy, and vibrating sample magnetometry. It was found that the particle size increases appreciably, and the crystallinity improves with Ti–Ru substitution. Mössbauer spectroscopy revealed that the substitution of Fe3+ ions occurs at the 4f 2 and 4f 1 +2a sites for low substitution, and substitution at the 2b site occurs for x ≥0.2. The saturation magnetization increases up to x =0.2, and then starts to decrease for higher x values, while the coercivity decreases monotonically, recording a reduction of 55% at x =0.4. These results were interpreted in terms of the site preferential occupation of the Ti2+ and Ru4+ ions. The thermomagnetic curves for all samples showed Hopkinson peaks indicating the presence of small superparamagnetic particles in the samples. The sample with x =0.0 was found to consist of purely superparamagnetic particles, while the substituted samples were found to contain only 22–30% of the powders’ mass as superparamagnetic particles. [Copyright &y& Elsevier]

Abstract: The structural and magnetic properties of barium hexaferrite nanoparticles (BaFe12−x Ga x O19) with x =0.0–1.0, prepared by ball milling were investigated using XRD, TEM, and VSM. It was found that the particles and crystallites have similar mean size of ∼41nm for all investigated samples. The saturation magnetization decreased slightly and nonlinearly with increasing x, and this was attributed to different preferential site occupation of Ga at low and high concentration ranges. The coercivity decreased slightly with increasing x for low concentrations of Ga (x ≤0.2), and then increased with increasing Ga concentration up to x =1.0. This behavior of the coercivity was attributed to the change in the exchange coupling, which was confirmed by the variation of SFD, remanence ratio and Curie temperature with Ga concentration in the samples. [Copyright &y& Elsevier]

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]

Abstract: Explicit solutions are derived for several phenomenological models of magnetization reversal in thin ferromagnetic films driven by a sawtooth magnetic field. For a domain wall velocity that is linear in the magnetic field, it is found that the dynamic coercive field follows a square-root power-law in the slope of the magnetic field, shifted by the depinning field. For a more general domain wall velocity different power-law exponents are found, yet the overall form for the scaling of the area of the hysteresis loop remains a power-law shifted by the depinning field. This shifted power-law could be interpreted to be a crossover between adiabatic and dynamic regimes. [Copyright &y& Elsevier]

Zero-field-cooled (ZFC) magnetization, field-cooled (FC) magnetization and coercive fields of Sr1−xCaxRuO3, with x=0.0, 0.2, 0.4 and 0.6, have been measured over the magnetic ordering temperature, in a sequence of applied fields. An empirical model has been proposed to analyze ZFC behaviors. The calculated ZFC magnetization is in agreement with the measured one. Different ZFC behaviors have been explained by means of the empirical model. [Copyright &y& Elsevier]

• Carbon in the t -Mn 53.3-x Al 45 C 1.7 Cr x phase stabilizes it and improves its magnetic properties. • The t -Mn 53.3-x Al 45 C 1.7 Cr x is instable for chromium contents higher than 1.0 atomic%. • Mn 53.3-x Al 45 C 1.7 Cr x samples are homogeneous with an average particle size between 108 to 127 µm. • Sample with 1.0 at.% Cr presents similar magnetic properties than those of the sample without Cr. • Sample with 1.0 at.% Cr can be used in application in which corrosion resistance is necessary. The effect of Cr doping, in melted and heat treated (HT) at different temperatures of Mn 57-x Al 43 Cr x with x = 0.51, 0.91, 1.51 and Mn 53.3-x Al 45 C 1.7 Cr x with x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5 alloys were studied. In samples with C and Cr (0 and 1.0 at.%) a paramagnetic epsilon phase (ε), and ferromagnetic tau phase (τ), with hard magnetic behavior, with coercive field Hc of 2.67 and 2.32 kOe, saturation magnetization Ms of 68 and 66 emu/g, remanent magnetization Mr of 39.6 and 33.6 emu/g, and product (BH)max of 0.91 and 0.69 MGOe, respectively, were observed. But for samples doped with Cr ≠ 1.0 at.% the metastable τ-phase partially decomposes into gamma (γ 2) and beta (β) phases. The samples have particle sizes between 108 and 127 µm. [ABSTRACT FROM AUTHOR]

We report structural and magnetic measurements on ZnFeO nanoparticles obtained through coprecipitation chemical method. The Rietveld analysis of X-ray patterns reveals that (i) our samples are single phase, (ii) the average particle size increases with synthesis temperature, and (iii) the cationic disorder increases with decreasing of the mean particle size. The Zero-Field-Cooled (ZFC) and Field-Cooled (FC) magnetization measurements show that the blocking temperature increases with increasing of the particle size and, to the sample grown at T=850 °C, it is possible to observe both Néel temperature to larger particles and blocking effects to smaller particles. Finally, we have observed that the coercive field does not decay with the square root of temperature following the Néel relaxation and Bean-Livingston approaches. [ABSTRACT FROM AUTHOR]