Anisotropy Constant K1 Research Articles

The magnetocrystalline anisotropy of Y2(FexCo1-x)17Hy compounds

The article presents the results of magnetocrystalline anisotropy (MCA) investigation of Y2(FexCo1-x)17 (x=0.03-0.50) rare-earth quasi-binary bulk crystal samples and their hydrides. The specific magnetization curves m(H) were measured in the wide temperature range for the original Y2(FexCo1-x)17 samples and for the corresponding hydrides. Magnetocrystalline anisotropy constants K1, K2 were calculated, temperature and compositional dependence curves were plotted based on m(H) data. The temperature dependences of specific saturation magnetization ms(T) and first anisotropy constant K1(T) were analyzed to determine temperature behavior patterns, estimate the Curie temperature Tc and predict the spin-reorientation transitions. The first anisotropy constant, saturation magnetization and Curie temperature compositional dependences of original Y2(FexCo1-x)17 and hydrogenated Y2(FexCo1-x)17Hy samples were compared to identify the hydrogenation effect on the magnetic properties of investigated compounds. The revealed patterns were explained in terms of the crystal structure of the compounds.

Τhe effect of Ni on the magnetic properties of power or high permeability MnZn ferrites

In this article an extensive study is presented on the Ni addition in three subcategories of MnZn ferrites under conditions of constant Mn/Zn ratio and Fe excess, namely i) low frequency (∼100 kHz) power ferrites, ii) medium frequency (∼500 kHz) power ferrites and iii) high permeability (μi ∼ 8000, 25 °C) ferrites. As found, Ni is a useful additive for optimizing the high temperature performance of MnZn ferrites since it increases Curie temperature, saturation flux density, magnetic permeability and decreases power losses at temperatures above 100 °C. In addition, the addition of Ni increases the resonance frequency and the frequency stability of the initial permeability and partly counteracts the ageing effects caused by Co, when it is present in medium frequency ferrites. The magnetic results are explained on the basis of Ni-substitutions on octahedral sites associated with a negative contribution to the total magnetocrystalline anisotropy, thereby shifting the temperature at which the magnetocrystalline anisotropy constant K1 changes sign, to higher temperatures. The morphological results are explained assuming that the presence of Ni is associated with decreased cation vacancy and increased anion vacancy concentrations.

Spin reorientation in GdMn2(Ge1-xSix)2 compounds

Structure and magnetic properties of layered GdMn2(Ge1-xSix)2 (0 ≤ x ≤ 1) compounds were studied. All the compounds crystallize in the tetragonal ThCr2Si2-type structure. It was shown by magnetization measurements at low temperature on quasi-single crystals that, with increasing Si concentration, the easy magnetization direction reorients from the c-axis to the basal plane. The spin reorientation occurs via an angular phase. A model of three magnetic sublattices coupled by negative intersublattice exchange interactions was used to describe the field dependences of the magnetization. For GdMn2Ge2 and GdMn2(Ge0.9Si0.1)2 in the fields applied along the c-axis, seven different magnetic structures were predicted, including two angular structures considered for the first time. The model explains formation of angular magnetic structures in zero field in GdMn2(Ge1-xSix)2 system by taking into account magnetic anisotropy of Mn sublattices with a positive anisotropy constant K1 and negative K2.

Substitution of Sn in the high-permeability MnZn ferrite for wide temperature applications

To meet the challenge of varied working temperatures of inductance components in new energy vehicle and 5G communication, the high-TC high-permeability MnZn ferrite with excellent temperature stability was developed by the addition of SnO2. In this series of samples, initial permeability μi maintains large values in a wide temperature range. With increasing the SnO2 content, the temperature of the second permeability peak Tsp decreases and meanwhile Curie temperature TC maintains as high as 160 °C. For the best sample with 6000 ppm SnO2, μi at 25 °C is 7244 and exhibits the excellent temperature stability with the low specific temperature coefficient of 0.35 × 10−6 °C−1 between 25 and 130 °C. The addition of SnO2 generates Fe2+ and adjusts the magneto-crystalline anisotropy constant K1 = 0 point, which is responsible for the wide-temperature high permeability. The effect of SnO2 addition on magnetization process has also been clarified.

Fabrication of half-metallic Co2FeAlxSi1–x thin film with small magneto-crystalline anisotropy constant K1

A tunnel magnetoresistance (TMR) sensor is a highly sensitive magnetic sensor workable at room temperature. To achieve smaller magnetic field detection, both a high TMR ratio and small magnetic anisotropy of the free layer are required. In this study, we developed single crystalline Co-based Heusler alloy Co2FeAlxSi1-x films as the free layer of TMR sensors and systematically investigated their crystalline and magnetic properties. The magnetic tunnel junction (MTJ) with these alloys is a promising device for highly sensitive TMR sensors due to their half-metallicity. We evaluated the B2 and L21 ordering parameters SB2 and SL21. SB2 was above 80 % for all the samples and SL21 was 48 % at a maximum, which indicates that all the samples exhibit half-metallicity. In addition, we evaluated their first magneto-crystalline anisotropy constant K1 from magnetization curves. K1 changed from positive to negative as Al component x increases and K1 was about 1200 erg/cc at x = 0.33. These results indicate that Co2FeAlxSi1-x films around x = 0.33 have a good candidate for the free layer of TMR sensors because of their half-metallicity and small magnetic anisotropy.

Effect of Ga substitution on grain orientation and magnetostrictive properties of polycrystalline CoFe2O4 ceramics prepared by the solid-state method

As a kind of magnetostrictive ceramics, cobalt ferrites are widely concerned because of its large magnetostriction and high resistivity, which are ideal for high-frequency applications. But, the high driving magnetic field due to the high magnetocrystalline anisotropy limits the practical applications of cobalt ferrites, thus, it is a still a challenge to find a balance between high magnetostriction properties and low driving magnetic fields. In this work, we investigated the effects of partially substitution of Ga3+ for Fe3+ on grain orientation and magnetic properties, attempting to maintain high magnetostriction while reducing the driving magnetic field. The CoFe2-xGaxO4 (x=0, 0.05, 0.1, 0.15) with single-phase spinel structure were prepared by the conventional solid-state method. The saturation magnetization MS increased with the increase of Ga concentration, meanwhile the coercivity Hc and magnetocrystalline anisotropy constant K1 significantly decreased, which indicates the better soft magnetic characteristics of the Ga-doped cobalt ferrites. The oriented CoFe2-xGaxO4 samples were obtained using magnetic field orientation technique during the powder forming process. The <001> preferred orientation was achieved in CoFe2O4 samples. However, the <001> orientation degree decreased with the substitution of Ga, and the preferred orientation has changed into <111> at x=0.15. The Ga substitution affected the magnetocrystalline anisotropy and grain orientation, thereby affecting the magnetostrictive properties. As for the non-oriented samples, although the maximum magnetostrictive strain slightly decreased with Ga substitution, while there was a significant drop in the magnetostrictive saturation field. However, the magnetostriction of the oriented samples decreased significantly with the substitution of Ga due to the change of grain orientation from <001> to <111>.

Dependence of the Structural and Magnetic Properties on the Growth Sequence in Heterostructures Designed by YbFeO3 and BaFe12O19.

The structure and the chemical composition of individual layers as well as of interfaces belonging to the two heterostructures M1 (BaFe12O19/YbFeO3/YSZ) and M2 (YbFeO3/BaFe12O19/YSZ) grown by pulsed laser deposition on yttria-stabilized zirconia (YSZ) substrates are deeply characterized by using a combination of methods such as high-resolution X-ray diffraction, transmission electron microscopy (TEM), and atomic-resolution scanning TEM with energy-dispersive X-ray spectroscopy. The temperature-dependent magnetic properties demonstrate two distinct heterostructures with different coercivity, anisotropy fields, and first anisotropy constants, which are related to the defect concentrations within the individual layers and to the degree of intermixing at the interface. The heterostructure with the stacking order BaFe12O19/YbFeO3, i.e., M1, exhibits a distinctive interface without any chemical intermixture, while an Fe-rich crystalline phase is observed in M2 both in atomic-resolution EDX maps and in mass density profiles. Additionally, M1 shows high c-axis orientation, which induces a higher anisotropy constant K1 as well as a larger coercivity due to a high number of phase boundaries. Despite the existence of a canted antiferromagnetic/ferromagnetic combination (T < 140 K), both heterostructures M1 and M2 do not reveal any detectable exchange bias at T = 50 K. Additionally, compressive residual strain on the BaM layer is found to be suppressing the ferromagnetism, thus reducing the Curie temperature (Tc) in the case of M1. These findings suggest that M1 (BaFe12O19/YbFeO3/YSZ) is suitable for magnetic storage applications.

Magnetic Anisotropy Tailoring by 5d-Doping in (Fe,Co)5SiB2 Alloys

Band-structure calculations were performed using the spin-polarized relativistic Korringa–Kohn–Rostoker (SPR-KKR) band-structure method, determining intrinsic magnetic properties, such as magnetic moments, magnetocrystalline anisotropy energy (MAE), and Curie temperatures, of Fe5−x−yCoxMySiB2 (M = Re, W) alloys. The general gradient approximation (GGA) for the exchange–correlation potential and the atomic sphere approximation (ASA) were used in the calculations. Previous studies have shown that for Fe5SiB2, the easy magnetization direction is in-plane, but it turns axial for Co-doping in the range 1 &lt; x ≤ 2.5 (y = 0). Furthermore, studies have shown that 5d-doping enhances the MAE by enabling the strong spin–orbit coupling of Fe–3d and M–5d states. The aim of the present theoretical calculations was to find the dependence of the anisotropy constant K1 for combined Co- and M-doping, building a two-dimensional (2D) map of K1 for 0 ≤ x ≤ 2 and 0 ≤ y ≤ 1. Similar theoretical 2D maps for magnetization and Curie temperature vs. Co and M content (M = W and Re) were built, allowing for the selection of alloy compositions with enhanced values of uniaxial anisotropy, magnetization, and Curie temperature. The magnetic properties of the Fe4.1W0.9SiB2 alloy that meet the selection criteria for axial anisotropy K1 &gt; 0.2 meV/f.u., Curie temperature Tc &gt; 800 K determined by the mean-field approach, and magnetization µ0Ms &gt; 1 T are discussed.

Giant coercivity induced by perpendicular anisotropy in Mn2.42Fe0.58Sn single crystals

We report the discovery of a giant out-of-plane coercivity in the Fe-doped Mn3Sn single crystals. The compound of Mn2.42Fe0.58Sn exhibits a series of magnetic transitions accompanying with large magnetic anisotropy and electric transport properties. Compared with the ab-plane easy axis in Mn3Sn, it switches to the c-axis in Mn2.42Fe0.58Sn, producing a sufficiently large uniaxial anisotropy. At 2 K, a giant out-of-plane coercivity (Hc) up to 3 T was observed, which originates from the large uniaxial magnetocrystalline anisotropy. The modified Sucksmith-Thompson method was used to determine the values of the second-order and the fourth-order magnetocrystalline anisotropy constants K1 and K2, resulting in values of 6.0 × 104 J/m3 and 4.1 × 105 J/m3 at 2 K, respectively. Even though the Curie temperature (TC) of 200 K for Mn2.42Fe0.58Sn is not high enough for direct application, our research presents a valuable case study of a typical uniaxial anisotropy material.

Aluminum and Zinc Co-substituted Cobalt Ferrite: Structural, Magnetic, and Magnetostrictive Properties

We report on the influence of Al and Zn co-substitution on the structural, magnetic, and magnetostrictive properties of cobalt ferrite (Co1–xZnxFe2–xAlxO4, 0 ≤ x ≤ 0.15; CZFAO) materials, which were made using a glycine-nitrate autocombustion process. The cubic spinel structure is present in both the as-synthesized and the sintered CZFAO samples, where it was evident that the crystallite size and lattice parameter reduced with increasing x due to the incorporation of smaller Al3+ ions in place of larger Fe3+ ions in spinel ferrite. Co-substitution induced changes in the metal–oxygen bond lengths, causing both the tetrahedral and octahedral infrared and Raman spectroscopic bands to shift toward higher wavenumbers. The electron microscopy analyses indicate that the Al–Zn substitution induces grain growth, leading to a dense, interconnected grain morphology. Mossbauer analyses indicate that the Al3+ occupies the octahedral site, whereas Zn2+ is substituted at the tetrahedral site. Due to equal magnetic dilution of both tetrahedral and octahedral sites caused by the presence of Zn and Al at the appropriate sites, the saturation magnetization MS of CZFAO is the same as that of pure CFO. All other magnetic parameters (coercivity HC, magnetocrystalline anisotropy constant K1, and Curie temperature TC) decrease with increasing x, where the decline observed is mostly due to superexchange interaction (A-O-B) reduction caused by the substituents’ non-magnetic character. CZFAO materials exhibit higher magnetostriction strain λ and strain sensitivity dλ/dH at relatively low magnetic fields; among all the samples, x = 0.15 demonstrates a maximum strain sensitivity of −2.53 × 10–9 m/A at 23 kA/m magnetic field. The composition-tuned CZFAO materials with desirable properties are suitable for application in torque sensors.

New Manufacturing Process for Granular Texture Management in Polycrystalline BaM Hexaferrites through the Goethite Crystallite Laths Aspect Ratio, and a Specialized Law of Approach to the Magnetic Saturation for Partly Polarized Uniaxial Materials

This study is aimed at the manufacture and the magnetic properties of polycrystalline M-type hexaferrites BaFe12O19 (barium ferrite, or BaM) materials of different magnetic texturing grades, going from a random distribution of the BaM crystallites to their almost complete stacking. Our target is to optimize the value of reduced-remanence magnetization MR/MS, which is among the most significant features of the self-polarized materials. In this study, we focus on the role played by the precursors hematite (isotropic spherical shape) and goethite (anisotropic lath shape). Therefore, 11 samples with a flat cylinder shape are fabricated, with an increasing hematite to goethite ratio. We demonstrate that this ratio drives the texturization of the samples by producing self-polarized materials with different MR/MS from the simple green compaction of the precursors, followed by a heat treatment. Most importantly, our study reveals the orientation of BaM particles after compaction; therefore, MR/MS, is strongly influenced by the aspect ratio of the lath-shaped goethite crystallites. Additionally, we show that finer goethite crystallites yield higher-value MR/MS. We optimize the aspect ratio of the goethite crystallites for an improved BaM texture. The optimization of the morphology of the goethite crystallites leads to an increase in the BaM particles’ orientation and stacking. The salient outcome of this work, which distinguishes it significantly from recent works, is that the particles stacking increases with the value of the shape factor η (defined as the ratio of the diameter of the laths to their length) of the goethite, evidenced by XRD results. The Rietveld refinements of powder diffractograms and the measured magnetic properties reveal a particle-stacking enhancement caused by not only the ratio of hematite: goethite but mainly by an optimal aspect ratio of the goethite crystallites. Based on this study, the BaM materials are further manufactured with a controlled magnetic texture; thus, they are partly self-polarized. They show reduced-remanence magnetization MR/MS varying from 0.5 and 0.81, while the angular dispersion of the BaM particles’ easy axis of magnetization varies from 60° to 10°. The magnetic properties of the samples are further studied in microwave experiments, from which the value of the magnetocrystalline anisotropy field HK = 16.6 kOe is deduced. The first magnetization curves of each sample are obtained using a VSM. A law of approach to the saturation suitable for the case of the uniaxial polycrystalline materials, and for which the particle stacking is only partial, is proposed for the fitting of the magnetization process. It is suggested that by using the proposed law with a known magnetocrystalline anisotropy constant K1, the angular grain-dispersion can be found.

Electrical Properties of Cobalt Substituted NZCF and ZNCF Nanoparticles Prepared by the Soft Synthesis Method

The soft chemical method was adopted for the synthesis of cobalt substituted nickel-zinc and zinc-nickel ferrites (Ni0.95-xZn0.05CoxFe2O4 and Zn0.95-xNi0.05CoxFe2O4 for x= 0.01, 0.02, 0.03, 0.04, 0.05, and 0.06. We have recently studied the structural, morphological, magnetic properties, initial permeability, and dielectric constant of the samples. They are found with cubic ferromagnetic spinel structure along with the morphology suitable for high-density recording media. The effective initial permeability μi (μeff) is found to depend on magnetocrystalline anisotropy constant K1 and grain size D. From this present study, the dc resistivity is found to increase linearly with Co2+ substitution for both ZNCF and NZCF ferrites up to x=0.04. After that, the material changes its ferromagnetism to paramagnetism thereby increasing the activation energy. The difference between the two magnetic states (Ferro and para) in NZCF is found to be greater than in ZNCF. The phase transition helps to determine the Curie temperature. The ac conductivity takes place by the hopping of charge carriers called polarons. The conductivity is enhanced with frequency.

A comparative study of Nd15Fe78B7 and Nd15Co78B7 systems: phase formations and coercivity mechanisms

Both Nd-Fe-B and Nd-Co-B nanocrystalline magnets exhibit coercivity above 1 T. While the microstructure and mechanism of the coercive force of Nd-Fe-B magnets are well known, the Nd-Co-B system is much less studied, and the microstructure and origin of the high coercive state in this material is not well understood. In this work, we selected Nd15Fe78B7 and Nd15Co78B7 alloys with simple and stable stoichiometries to reveal the similarities and differences between these two systems. For this study, melt-spun nanocrystalline ribbons, hot-compacted magnets and bulk materials crystallized from the amorphous precursor were used. The coercivity of Nd15Fe18B7 alloy is in the range of 0.9–1.7 T, while for Nd15Co18B7 it was of 0.5–1.0 T. Electron microscopy and atom probe tomography analyses indicate that, in contrast to conventional Nd15Fe78B7, where the ferromagnetic Nd2Fe14B phase is the dominant matrix phase and the Nd-rich phase distributes along the grain boundaries providing magnetic decoupling, the Nd15Co18B7 alloys comprise of three randomly redistributed exchange-coupled ferromagnetic phases: Nd2Co14B, NdCo5 and NdCo4B. Single crystals of all constituent phases were grown and their spontaneous magnetization Ms and anisotropy constant K1 were determined. Using these measured intrinsic parameters and real nanostructure of Nd15Fe78B7 and Nd15Co78B7 alloys, micromagnetic simulations were carried out in order to reveal the differences in the coercivity mechanisms in these two distinctly different systems.

Dielectric and temperature dependent magnetic studies of Al3+ substituted Ba0.4La0.1Sr0.5AlxFe12-xO19 hexaferrite for microwave application

The Al3+ substituted polycrystalline Ba0.4La0.1Sr0.5AlxFe12-xO19 (0 ≤ x ≤ 1) hexaferrite sample were prepared by the solid-state method. The structural, morphology, dielectric, and temperature dependent magnetic properties are studied systematically. The XRD and Rietveld refinement analysis revealed that all the samples have magneto plumbite hexaferrite structure with space group P6/mmc. The lattice parameters a and c are decreased from 5.888 Å to 5.874 Å and 23.109 Å to 23.085 Å, respectively. The c/a ratio is found to be between 3.92 and 3.93, which is ideal for M−type hexaferrite. It is observed that all the Raman peaks are shifted along the higher wavenumber with increasing Al3+ substitution. The surface morphology of these samples has uniform grain sizes and is closely packed. Also, all the constituent elements are present in proper composition except barium, which has a little higher atomic percentage than the calculated value. The complex dielectric constant (ε', ε“) decreased with Al3+ insertion (for x = 0: ε' = 3.44 k, ε” = 0.993 k; x = 1: ε' = 0.744 k, ε“ = 0.211 k @ 1 MHz). The hysteresis isotherm curves were analyzed by the law of approach to saturation magnetization in the temperature range of 10 K − 300 K. Further, the saturation magnetization and magnetic anisotropy constant K1(T) are found to be decreased, whereas anisotropy field Ha(T) and coercivity HC(T) are rises with an increase in temperature as well as Al3+ concentration. The Bloch’s spin wave theory is used to analyze temperature dependent saturation magnetization, and all the samples get deviated from Bloch’s T3/2 law as well as modified Kobler’s Bloch law. It might be due to finite size effects, long wavelength excitation, and the introduction of constant energy gap into spin wave spectrum, geometrical asymmetries, and other atomic disorders. Finally, Dyson’s approximation which includes T5/2 terms is perfectly fitted with the experimental data. The analysis makes it possible to predict the curie temperature and visualize the nature of the ferromagnetic coupling with the increasing Al3+ concentrations. Above that, the temperature dependent magnetic anisotropy constant K1(T) is linearly fitted with cubic of temperature dependent saturation magnetization MS(T), which confirmed that all the samples have uniaxial hexagonal crystal symmetry. The combination of magnetic and dielectric responses made the material suitable for permanent magnets and microwave applications.

Guidelines for attaining optimal soft magnetic properties in FeAlSi films

Nm-order FeAlSi epitaxial films with a partially D03-ordered structure were grown on MgO substrates, and ideal soft magnetic properties were obtained. We found that the sign of the magnetocrystalline anisotropy constant K1 changes with increasing annealing temperature for certain FeAlSi compositions. This is caused by a change in the volume balance of the ordered phases with the annealing process and the point at which K1 ∼ 0 shifts to the Al-rich concentration as the degree of D03-ordering decreases. K1 was precisely measured by ferromagnetic resonance under the optimal condition, and the value of 1.6 × 102 (erg/cc) was obtained, which is comparable to that of bulk. The uniaxial component of the magnetic anisotropy due to magnetostriction was small, and a fourfold symmetric component due to magnetocrystalline anisotropy was dominant.

Effect of sintering temperature on microstructure and magnetic and dielectric properties of M-type barium ferrites

In this study, the effect of sintering temperature on microstructure, magnetic properties and dielectric behavior of M-type barium ferrites (BaM) is systematically analyzed. BaBi0.45(CoTi)1.2Fe9.15O19 samples with a dense microstructure and typical hexagonal shape are obtained at the sintering temperature of 920 °C. Moreover, the permittivity (ε′) of BaM increases to 21.41 at 0.01 GHz and the permeability (μ′) increases to 10.82 at the optimized temperature of 920 °C. Based on mathematical fitting, the saturation magnetization (4πMs) of samples is calculated to be 3272.27 Gauss and the magnetocrystalline anisotropy constant K1 is found to be 4.18 × 106 erg cm−3. More interestingly, the magnetic loss angle tangent (tanδμ) is reduced to 2.7 × 10−1 and the dielectric loss angle tangent (tanδε) is reduced to 5.8 × 10−3. The optimized magnetic and dielectric properties, with low losses, enhance the suitability of BaM ferrites for miniaturized microstrip devices.

Structure, magnetic anisotropy and magnetocaloric effect of Mn5Ge3-xSix single crystals

Magnetocaloric polycrystalline materials based on Mn5Ge3 have been widely studied due to their potential application for room temperature magnetic refrigeration. However, many investigations are performed on polycrystalline materials and thus the strong anisotropy in this layered structure is usually neglected. In this study, Mn5Ge3-xSix (x = 0, 0.7) single crystals were successfully synthesized via Sn flux and characterized by single-crystal X-ray diffraction and magnetic measurements. The Si substitution does not change the structural symmetry, but reduces the shortest Mn − Mn distances. As described by the Bethe-Slater curve, the reduction of the shortest Mn − Mn distances leads to weaker magnetic exchange, accounting for the lower ordering temperature. The magnetocrystalline anisotropy was evaluated by the Sucksmith and Thompson method, and became smaller upon substitution. The anisotropy constants K1 and K2 of Mn5Ge3-xSix (x = 0, 0.7) single crystals are positive, and decrease with the temperature. The electron paramagnetic resonance spectra suggest high spin d5 configuration of manganese in both crystals. The easy magnetization direction yields much larger maximum entropy changes in both crystals: 6.0 J/kg K for the pristine and 5.4 J/kg K for the substituted under an applied field of 30 kOe.

Effects of particle morphology and magnetocrystalline anisotropy on < 111 > orientation and magnetostriction of sintered Tb-Dy-Fe/DyCu compacts

Sintered Tb-Dy-Fe materials prepared by the compression molding method have higher relative density and energy density than powder-bonded composites. However, due to the low magnetocrystalline anisotropy and the cubic symmetry of the Laves structure, the orientation degree of sintered materials is relatively low and not beneficial for obtaining large magnetostriction. We prepared the sintered Tb-Dy-Fe/DyCu compacts with preferred <111 > orientation by applying magnetically oriented powder metallurgy. The dependence of orientation degree and magnetostriction of oriented Tb-Dy-Fe/DyCu sintered compacts on different particle morphology and Tb/Dy ratios were studied. The oriented Tb-Dy-Fe/DyCu sintered compacts prepared from the milled single crystal Tb-Dy-Fe powders gained a higher <111 > orientation due to the small rotational resistance when magnetic particles move in a magnetic field, achieving improved magnetostriction. Magnetocrystalline anisotropy which determines the rotational torque caused by the magnetic field is one of the important factors affecting the rotation behavior of magnetic particles in a magnetic field. We designed Tb-Dy-Fe alloys with different Tb/Dy ratios which have different magnetocrystalline anisotropy, and prepared the sintered Tb-Dy-Fe/DyCu compacts under the same process parameters. The magnetocrystalline anisotropy constant K1 of TbxDy1-xFe1.95 (x = 0.27, 0.30, 0.33, 0.50) alloys increased from 0.66 × 106 J/m3 to 3.85 × 106 J/m3 by raising the Tb/Dy ratios, and the <111 > orientation degree of sintered Tb-Dy-Fe/DyCu compacts was promoted simultaneously. The oriented Tb0.33Dy0.67Fe1.95/DyCu sintered compact achieved the highest <111 > orientation degree of 56.6%, resulting in the largest magnetostriction of 1326 ppm and the d33 peak value of 6.81 nm/A.

Pseudo magnetic properties and evidence for vortex state in Fe2NiGe Heusler alloy thin films

We report on the anisotropy, pseudo magnetic properties and formation of vortex state in Fe2NiGe thin films. From the torque measurements, estimated anisotropy constants K1 and K2 are found to be 4.47 × 103 J/m3 and −1.98 × 102 J/m3 respectively. Pseudo magnetic properties such as pseudo hysteresis work and pseudo remanence work infer that motion of domain wall in Fe2NiGe is rather smooth. The crest height and trough depth coefficient from the second stage of magnetization curves are estimated and are found to be 9.44 × 106 (A/m).mT and 8.76 × 106 (A/m).mT respectively. First order reversal curves infer switching field distribution is very small, which infers that less dislocations and more grain size. Indeed, the vortex state is evident from the contour graph of the first order reversal curves. We believe present results would be helpful for the future spintronic devices based on Heusler alloy thin films.

Substrate orientation dependent characteristics of half-metallic and metallic superlattices [La0.7Sr0.3MnO3/LaNiO3]10

We report a detailed study on the orientation dependent growth characteristics, electronic structure, transport, magnetic, and vibrational excitations in atomically flat interfaces of [La0.7Sr0.3MnO3/LaNiO3]10 superlattices (SLs) coherently grown on (001/011/111)-SrTiO3 substrates by the pulsed laser deposition technique. X-ray reflectometry confirms the periodic superlattice stacks from the Kiessig interference fringes and well-defined even interfaces between the nickelate and manganite layers. A complex local atomic environment across the interfaces was noticed, yet trivalent La, divalent Sr, and mixed valent Ni2+/3+ and Mn3+/4+ electronic states prevail at the core level with enhanced relative intensity ratio of the Mn ions in the superlattices grown on (111) oriented SrTiO3 substrates as compared to those grown on (001) and (011) oriented SrTiO3. The temperature (5≤T≤300K) dependence of electrical resistivity ρ(T) analysis reveals 3D variable range hopping model [ρ(T)=ρ0exp⁡(T0/T)(1/4)] with large magnitude of hopping energies (≥40 meV) for the SL-111 system associated with the high energy gap developed by the accumulation of disorderness in the individual constituents of polar layers. Moreover, all SL systems exhibit reduced ferromagnetic ordering temperatures (67≤TC≤110K) with a low-temperature anomaly (11.4≤T∗≤22K) and a substantial enhancement in the effective exchange interaction (Jeff∼3.52meV) having altered ground state-spin configuration S∼1/2 different from S=3/2 of La0.75Sr0.25MnO3. Nevertheless, the SL-011 system exhibits large anisotropy field HK∼18kOe and cubic anisotropy constant K1∼9.3×103J/m3 in comparison to the other two orientations. The second order two-phonon interaction driven by the local polaronic distortion causes significant changes in the vibrational excitations of the investigated system. Nonetheless, most of the Raman modes follow the substrate-induced, highly oriented epitaxial growth pattern except for two modes ν4 (326cm−1) and ν8 (728cm−1), which slightly differ in the case of SL-111 superlattices.