Easy Magnetization Direction Research Articles

Experimental study of the diamagnetism and the ferromagnetism in MoS2 thin films

A series of MoS2 films were prepared by the chemical bath deposition method at different temperatures (60–80 °C). The film thicknesses range from 0.988 up to 10.25 µm. The films are polycrystalline. Vibrating sample magnetometer (VSM) was used to study the magnetic properties of these MoS2 films. The experiments were done at room temperature with the magnetic field applied in the film plane. The magnetization curves indicate the coexistence of ferromagnetism and diamagnetism. The saturation and remnant magnetizations, the coercive and saturation fields as well as the diamagnetic susceptibility have been measured and are discussed as a function of the film thickness and the synthesis temperature. A change in the magnetic anisotropy is observed, and the magnetization easy axis direction switches from in-plane to out-of-plane as the thickness increases. The magnetic properties are correlated with the structural ones.

Magnetic phase diagram of the antiferromagnet U2Rh2Pb

A new U-based compound of the U2Rh2Pb, a new compound of the U2T2X series (T – transition metal, X – Sn, In, Pb), was prepared in a single-crystal form. Its structure was determined as belonging to the tetragonal Mo2FeB2 structure type with the shortest U–U spacing along the c-axis. The crystals were subjected to study of magnetic, specific heat, and electrical resistivity in various magnetic fields. U2Rh2Pb undergoes an antiferromagnetic transition at a Néel temperature TN of 20 K and exhibits an enhanced Sommerfeld coefficient γ ≈ 150 mJ/molK2. In contrast to the two rhodium analogues U2Rh2In and U2Rh2Sn, the easy-magnetization direction is the c-axis with rather low value of the critical field Hc = 4.3 T of the metamagnetic transition of a spin-flip type. The observed dependences of TN and Hc on temperature and magnetic field have been used for constructing a magnetic phase diagram. The experimental observations are mostly supported by first-principles calculations.

Highly spin-polarized electronic structure and magnetic properties of Mn2.25Co0.75Al1-x Ge x Heusler alloys: first-principles calculations.

Highly spin-polarized half-metals (HMs) and spin-gapless semiconductors (SGSs) are the promising candidates in spintronic devices. However, the HM and SGS Heusler materials are very sensitive to the stoichiometric defects and lattice distortion, which will be not beneficial to the practical applications. Here, the electronic structure and magnetic properties of Mn2.25Co0.75Al1−xGex (x = 0, 0.25, 0.50, 0.75 and 1.00) Heusler alloys were investigated by first-principles calculations. Large negative formation energy, cohesive energy and phonon spectra confirm that the Mn2.25Co0.75Al1−xGex alloys are stable. It is found that Mn2.25Co0.75Al1−xGex with x = 0, 0.25, 0.75 and 1.00 show robust ferrimagnetic HM characteristics, while Mn2.25Co0.75Al0.5Ge0.5 shows robust SGS characteristic. Under the hydrostatic and uniaxial strains, Mn2.25Co0.75Al1−xGex exhibit a series of rich electronic transitions. The magnetic anisotropy of Mn2.25Co0.75Al1−xGex turns from the in-plane [100] direction to the out-of-plane [001] one by applying the uniaxial strains. The results suggest that the complete spin polarizations of Mn2.25Co0.75Al1−xGex alloys are robust against the stoichiometric defects and lattice distortion, which have potential applications in spintronic devices.

Coercivity Mechanism of Ga-Doped Nd-Fe-B Sintered Magnets

The alignment dependence and angular dependence of coercivity (ALDC and ANDC, respectively) of aligned and isotropically aligned Ga-doped Nd14.79Ga0.57B5,24Co1.11Febal sintered magnets were analyzed, and the results were compared with those of ferrite magnets, which were reported in our previous paper. The coercivity of Ga-doped Nd-Fe-B magnets decreases as alignment improves. The ALDC of this magnet is similar to that of ferrite magnets. The angle of the magnetization-reversal area (AMRA) of the aligned Ga-doped magnets has at coercivity an angular tilt of 41.4°, which is wider than that of the ferrite magnets. The ANDC of Ga-doped Nd-Fe-B sintered magnets displays similar behavior with that of ferrite magnets but is slightly lower than that of ferrite magnets, which is expected from AMRA of Ga-doped Nd-Fe-B sintered magnets. These results support our proposed coercivity mechanism; specifically, the magnetic domain walls are pinned at grains with tilted easy magnetization directions or $c$ -axis tilted from the easy magnetization of the magnet. When the magnetic domain walls are de-pinned from the pinning sites, they jump through several grains, thereby determining the coercivity.

Neutron Diffraction Investigation of the DyFe11Ti Magnetic Structure and Its Spin Reorientations

Abstract In this article, we report on the magnetic structure of DyFe11Ti and its thermal evolution as probed by neutron powder diffraction. A thermodiffraction technique was used to follow the temperature dependence of the magnetic moments, as well as their orientation. The Dy and Fe moments were coupled to each other in an antiparallel manner to form a ferrimagnet, where the easy magnetization direction at 2 K was the [110] axis in the basal (a, b) plane. This magnetic structure underwent two successive spin reorientation phenomena with increasing temperature. A large Dy magnetic moment of 9.7 Bohr magneton (μB) was obtained at low temperatures, and the magnitude decreased rapidly to 7.5μB at 200 K. The largest Fe magnetic moment was observed on the Fe 8i position. A ThMn12-type crystal structure was preserved in the studied temperature range, despite the large changes of the magnetic structure. A sharp tilt was observed at the first-order spin reorientation, TSR1; the angle between the easy magnetization axis and the crystal c axis was reduced from 90° at 2 K to about 20° at 200 K (where c is the easy axis above 200 K); and the Dy and Fe magnetic moments maintained an antiparallel coupling.

Influence of Tb on easy magnetization direction and magnetostriction of PrFe1.9 alloy**Project supported by the National Natural Science Foundation of China (Grant No. 51901052) and the Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant No. 2018GXNSFAA281294).

The crystal structures, magnetization, and spontaneous magnetostriction of ferromagnetic Laves phase Pr1 − xTbxFe1.9 compounds are investigated in a temperature range between 5 K and 300 K. High resolution synchrotron x-ray diffraction (XRD) analysis shows that different proportions of Tb in Pr1 − xTbxFe1.9 alloys can result in different easy magnetization directions (EMD) below 70 K, i.e., [100] with x = 0.0, and [111] with x ≥ 0.1. This indicates Tb substitution can lead the EMD to change from [100] to [111] with x rising from 0.0 up to 0.1. The Tb substitution for Pr reduces the saturation magnetization Ms and the magnetostriction to their minimum value when x = 0.6, but it can increase low-field (0 ≤ H ≤ 9 kOe, the unit 1 Oe = 79.5775 A · m−1) magnetostriction when x = 0.8 and 1.0 at 5 K. This can be attributed to the larger magnetostriction of PrFe1.9 than that of TbFe1.9, as well as the decrease of the resulting anisotropy due to Tb substitution at low temperatures.

Mössbauer Spectroscopy of Triphylite (LiFePO4) at Low Temperatures

Low temperature magnetic ordering in the LiFePO 4 compound is investigated experimentally using Mössbauer spectroscopy and theoretically via first principles calculations. The evaluation of experiment carried out on a powder sample is compatible with an antiferromagnetic order of Fe ion magnetic moments. When an external magnetic field is applied, Fe magnetic moments start to deviate slightly from the [010] easy magnetization direction. These findings are confirmed by means of first principles calculations, which also suggest the magnitude of single ion magnetic anisotropy and orbital and spin-dipolar contributions to the magnetic hyperfine field, which is eventually in a good agreement with the experiment. Diffraction and magnetic measurements complement the study.

The magnetic properties of Fe3O4 thick films as described by third order perturbed Heisenberg Hamiltonian

Thick films of Fe3O4 up to 10000 spin layers have been explained using third order perturbed modified Heisenberg Hamiltonian with seven magnetic parameters. Total magnetic energy and orientation of magnetic easy directions were determined for spinel structure of Fe3O4 with octahedral and tetrahedral sites. The effect of number of spin layers and stress induced anisotropy on magnetic properties was investigated. 3-D plot of energy versus angle and number of spin layers was plotted to determine the number of spin layers corresponding to minimum magnetic energy. Magnetic easy axis was found by plotting a graph of energy versus angle for one particular value of the previously-mentioned number of spin layers. Similarly, 3-D and 2-D graphs were plotted for stress induced anisotropy. For film with 4 spin layers, magnetic easy directions were found to be θ = 2.3, 2.5, 5.6 radians, …. When the ratio of stress induced anisotropy to strength of long-range dipole interaction is 2, magnetic easy direction was found to be θ = 2.6 radians. Here the angles were measured with respect to a line drawn normal to the film plane. Because Fe3O4 is a soft magnetic material, Fe3O4 finds potential applications in magnetic memory devices.

Rotating magnetocaloric effect and thermal transport properties in sintered Nd0.8Pr0.2Co5 alloy

We report microstructure, magnetocaloric effect and thermal transfer properties of highly orientated Nd0.8Pr0.2Co5 alloy prepared by powder metallurgical processing. Two spin-reorientation transitions of easy magnetization direction, easy plane to easy cone at TSR1 = 206 K, easy cone to easy axis at TSR2 = 242 K, are observed. The present textured alloy exhibits a rotating entropy change of 2.6 J/(kg·K) and refrigerant capacity of 155 J/kg under a magnetic field of 2 T, and high thermal conductivity of 11 W/(m·K). The sintered Nd0.8Pr0.2Co5 alloy with good combination of excellent magnetocaloric and thermal transfer properties are promising for scientific research and practical applications as room-temperature rotating magnetic refrigeration materials.

Electrodeposition of equiatomic FeNi and FeCo nanowires: Structural and magnetic properties

In the present work, equiatomic FeNi and FeCo magnetic nanowires (NWs) have been electrodeposited in Anodic Aluminum Oxide (AAO) membranes with 70 nm pore size. The role of the electroactive species Ni2+ and Co2+ on the anomalous codeposition behavior in thin films and nanowires has been discussed and compared. Field Emission Gun-Scanning Electron Microscope (FEG-SEM), X-ray diffraction (XRD) and Vibrating Sample Magnetometer (VSM) were used to evaluate the morphology, composition, crystalline structure and magnetic properties of the materials. SEM-FEG analysis showed very homogeneous NWs lengths for both FeNi and FeCo NWs, Energy dispersive X-ray spectroscopy (EDS) analysis revealed a stable composition along the FeCo NWs and a change in composition along the FeNi NWs. The XRD patterns indicate the predominance of the bcc structure for both alloys. Except for additional peaks of fcc phase found on FeNi alloy, the same crystalline bcc structure is observed after annealing treatment of 300 °C during 20 h. TEM analysis confirmed the ordered character of the bcc FeCo alloy. The hysteresis loops show an easy magnetization direction parallel to the wires due to the predominance of the shape anisotropy. The coercive field (Hc) of FeNi NWs increases with the length of the wires while that of FeCo NWs decreases. The annealing treatment doesn’t affect the magnetic properties of FeNi NWs, whereas a remarkable increase in the coercivity of the FeCo NWs is observed.

Structural and Uniaxial Magnetic Anisotropy of Co1-XMgX(X = 0.04–0.12) Nanowires in Alumina Templates

The nanoporous anodized aluminum oxide (AAO) templates were synthesized by two-step anodization in a solution of 0.5 M phosphoric acid at 60 V and temperature T ~ 0 °C. The CoMg nanowires were synthesized by template-based AC Electrodeposition technique at different voltages by AC source 13–17 V at room temperature. These CoMg nanowires were investigated via different characterization techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). The SEM result shows that nanowires have average diameter about 150 nm and length about 23 μm. The EDX reveals that nanowires only consisted of Mg and Co atoms, and atomic ratio of Mg/(Co + Mg) showed increasing tendency with deposition voltage which depicts that higher AC electrodeposition voltage is more suitable for Mg-rich deposition. The XRD results show that CoMg nanowires have hexagonal crystal structure with polycrystalline nature. The MH loops confirm that nanowires are soft ferromagnetic with uniaxial magnetic anisotropy. It is observed from angular dependence of coercivity that magnetization reversal mechanism occurs by a combination of curling and nucleation mode. The squareness (Mr/Ms) is found to be 0.24 along nanowires and 0.16 perpendicular to nanowire axis suggesting that easy magnetization direction lies along the nanowires. The effective anisotropy is observed along the nanowire axis due to dominance of shape anisotropy and suppression of dipole-dipole interactions among nanowires.

Orbital Magnetic Moments in Strained SrRuO3 Thin Films

We carried out x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy and evaluated orbital magnetic moments in compressively strained tetragonal and tensilely strained monoclinic SrRuO3 epitaxial thin films whose magnetic easy axis directions and behavior of the transverse resistivity differ from each other. We found that regardless of the types of the strain, SrRuO3 films have negative orbital magnetic moments arranged antiparallel to the spin magnetic moments along the magnetic easy axis directions. The magnitudes of the orbital moments for both films are similar: ∼−0.17 μB/Ru at 20 K. These observations indicate that the films’ structures tie only to the direction of the orbital magnetic moments and consequently determine the magnetic easy axis direction in SrRuO3 through the strong magnetocrystalline effect. This highlights the significance of the orbital magnetic moment as a factor determining of the magnetic anisotropy of this oxide. Our results provide important physical insight into magnetic and magneto-transport properties of SrRuO3.

Bonded magnets with circumferential magnetic anisotropy

Abstract This paper describes a method of producing circumferentially oriented magnetic hard composites (bonded magnets). This means that the directions of easy magnetization of the magnetically hard particles contained in the magnet are perpendicular to the radius and to the axis of the cylindrical sample (parallel to the direction tangential to the surface of the cylinder). Tests were carried out on two magnetically hard materials (Nd-Fe-B and barium ferrite) with two different volumes of the solid phase in the slurry. The bonded magnets were produced by the centrifugal casting of the slurry in a constant magnetic field. The obtained shapes, in the form of cylinders, possessed a well compacted hard magnetic layer, with a thickness depending on the powder content in the slurry. In all cases, the remanence of the obtained samples was the highest in the circumferential direction, i.e. perpendicular to the longitudinal section of the cylinder. X-ray investigations revealed that the samples obtained have a crystallographic texture. A model of phenomena occurring during centrifugal casting of slurry in a magnetic field was proposed, which explains the structure of the obtained materials is shaped.

MnBi hard magnetic films optimised through the correlation between resistivity, morphology and magnetic properties

Abstract Hard magnetic MnBi films were fabricated using pulsed laser deposition (PLD). The films consisted of Mn/Bi bilayers and the thickness of each sample constant was 185 nm. The number of bilayers (5 to 80 bilayers) and consequently, the thickness of the Mn and Bi layers changed among the different samples, although the proportion of Mn and Bi remained constant in each bilayer. The structural and morphological changes in the Mn/Bi multilayered films were produced by thermal treatments and were monitored by measuring the change in their resistance as a function of the temperature. These measurements, along with the magnetic measurements, allowed us to determine the optimum heat treatments that induced the formation of the low temperature (LT) α-MnBi phase. A maximum value of both the magnetisation (460 emu/cm3) and the maximum BH product (46 kJ/m3) was observed in the sample with 40 bilayers, showing, in addition, a magnetic anisotropy, wherein the easy magnetisation direction was predominantly perpendicular to the plane of the sample. A detailed explanation of these changes and of the atomic diffusion processes present for such optimisation has been achieved.

Dynamic magnetoelastic properties of TbxHo0.9−xNd0.1(Fe0.8Co0.2)1.93/epoxy composites

Abstract TbxHo0.9−xNd0.1(Fe0.8Co0.2)1.93/epoxy (0 ⩽ x ⩽ 0.40) composites are fabricated in the presence of a magnetic field. The structural and dynamic magnetoelastic properties are investigated as a function of both magnetic bias field Hbias and frequency f at room temperature. The composites are formed as textured orientation structure of 1–3 type with 〈1 0 0〉 preferred orientation for x ⩽ 0.10 and 〈1 1 1〉-orientation for x ⩾ 0.25. The composites generally possess insignificant eddy-current losses for frequency up to 50 kHz, and their dynamic magnetoelastic properties depend greatly on Hbias. The elastic modulus (E3 H and E3 B) shows a maximum negative ΔE effect, along with a maximum d33, at a relatively low Hbias ~ 80 kA/m, contributed by the maximum motion of non-180° domain-wall. The 1–3 type composite for x ⩾ 0.25 shows an enhanced magnetoelastic effect in comparison with 0 to 3 type one, which can be principally ascribed to its easy magnetization direction (EMD) towards 〈1 1 1〉 axis and the formation of 〈1 1 1〉-texture-oriented structure in the composite. These attractive dynamic magnetoelastic properties, e.g., the low magnetic anisotropy and d33 , max as high as 2.0 nm/A at a low Hbias ~ 80 kA/m, along with the light rare-earth Nd element existing in insulating polymer matrix, would make it a promising magnetostrictive material system.

Crystal field coefficients for yttrium analogues of rare-earth/transition-metal magnets using density-functional theory in the projector-augmented wave formalism

We present a method of calculating crystal field coefficients of rare-earth/transition-metal (RE-TM) magnets within density-functional theory (DFT). The principal idea of the method is to calculate the crystal field potential of the yttrium analogue (‘Y-analogue’) of the RE-TM magnet, i.e. the material where the lanthanide elements have been substituted with yttrium. The advantage of dealing with Y-analogues is that the methodological and conceptual difficulties associated with treating the highly-localized 4f electrons in DFT are avoided, whilst the nominal valence electronic structure principally responsible for the crystal field is preserved. In order to correctly describe the crystal field potential in the core region of the atoms we use the projector-augmented wave formalism of DFT, which allows the reconstruction of the full charge density and electrostatic potential. The Y-analogue crystal field potentials are combined with radial 4f charge densities obtained in self-interaction-corrected calculations on the lanthanides to obtain crystal field coefficients. We demonstrate our method on a test set of ten materials comprising nine RE-TM magnets and elemental Tb. We show that the calculated easy directions of magnetization agree with experimental observations, including a correct description of the anisotropy within the basal plane of Tb and NdCo5. We further show that the Y-analogue calculations generally agree quantitatively with previous calculations using the open-core approximation to treat the 4f electrons, and argue that our simple approach may be useful for large-scale computational screening of new magnetic materials.

Gd2Te3: an antiferromagnetic semimetal

We report high-precision magnetization (), magnetic susceptibility (), specific heat (Cp (T, H)) and ‘zero-field’ electrical resistivity, , data taken on Gd2Te3 single crystal over wide ranges of temperature and magnetic field (H), with either -axis or -plane. and unambiguously establish that the b-axis is the easy direction of magnetization whereas any direction in the ac-plane is a hard direction. The -type anomaly in ‘zero-field’ specific heat, Cp (T, H = 0), and an abrupt drop in (characteristic of the paramagnetic (PM) — antiferromagnetic (AFM) phase transition) are observed at the Néel temperature, K. and Cp (T,H) clearly demonstrate that shifts to lower temperatures with increasing H irrespective of whether H points in the easy or hard direction. When , the isotherms at temperatures in the range 2.5 K K reveal the existence of a field-induced spin-flop (SF) transition at fields 4.0 T 4.5 T. The first principles electronic band structure and density of states calculations, based on the density functional theory, correctly predict an AFM ground state (stabilized primarily by the 4f Gd3+ – 5p Te2−– 4f Gd3+ superexchange interactions) and the observed semi-metallic behavior for the Gd2Te3 compound. Moreover, these calculations yield the values for the ordered magnetic moment per Gd atom at T = 0, mJ mol−1 K−2 for the Sommerfeld coefficient for the electronic specific heat contribution and K for the Curie–Weiss temperature, respectively. These theoretical estimates conform well with the corresponding experimental values , mJ mol−1 K−2 and K.

Photo-induced anomalous Hall effect in nickel thin films

Abstract Anomalous Hall effect is commonly used as a simple technique to study the magnetization reversal of perpendicularly magnetized thin films. Yet, in most applications, the easy-magnetization direction is in the film-plane. We here propose photo-induced anomalous Hall effect as a new magneto-metric technique to reconstruct the in-plane magnetization loop of metallic thin films. Nickel thin films were deposited on intrinsic silicon to form a Schottky contact. Photo-induced Hall voltage was found hysteretic with the in-plane, magnetic field. The measured voltage-loop was found to mimic the magnetization loop as measured by a magnetometer.

Magnetostructural behavior in the non-centrosymmetric compound Nd7Pd3

A systematic study of the physical properties and microscopic magnetism of Nd7Pd3 compound, which in the paramagnetic state crystallizes in the non-centrosymmetric hexagonal Th7Fe3-type structure (hP20–P63mc; with a = 10.1367(1) Å and c = 6.3847(1) Å at 300 K), confirms multiple magnetic ordering transitions that occur upon cooling. Antiferromagnetic transition is observed at TN = 37 K, which is followed by ferromagnetic transformation at TC = 33 K. The first-order magnetic transition at TC is magnetoelastic: it involves a change of crystal symmetry from P63mc to Cmc21 and leads to anisotropic changes of the unit cell parameters. While the antiferromagnetic structure is symmetry allowed in P63mc, the ferromagnetic structure with magnetic moments along the a-direction of the original hexagonal unit cell induces the first order transition to Cmc21. Density functional theory calculations confirm the experimentally observed ground state with the a-axis as the easy magnetization direction.

Magnetic Properties of the Fe63.5Ni10Cu1Nb3Si13.5B9 Alloy Nanocrystallized in the Presence of Tensile Stresses

The effect of 10 at % Ni, which was introduced into the classic Finemet Fe73.5Cu1Nb3Si13.5B9 at the expense of the Fe content, on the magnetic properties of the composition has been considered. The alloy was subjected to nanocrystallizing annealing in the presence of tensile stresses and in their absence. It is shown that, similarly to the Ni-free alloy, in the Fe63.5Ni10Cu1Nb3Si13.5B9 alloy subjected to thermomechanical treatment, the magnetic anisotropy with the easy magnetization direction across the ribbon axis (transverse induced magnetic anisotropy) is induced. It was found that the 10 at % Ni addition almost does not affect the value of magnetic anisotropy constant induced under thermomechanical treatment and decelerates the process of magnetic anisotropy inducing at σ ≤ 200 MPa. The Ni-containing alloy subjected to nanocrystallizing annealing (at 520°C) in the presence of tensile stresses and in their absence demonstrates the more than 200-fold increase in the coercive force as the annealing time increases from 1 to 4 h, whereas the coercive force of the Ni-free alloy is almost unchanged. This is likely to be related to the appearance of new structural components in the Ni-alloyed composition upon annealing.