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Magnetic semiconductors with high critical temperature have long been the focus in materials science and are also known as one of the fundamental questions in two-dimensional (2D) materials. Based on density functional theory calculations, we predict a 2D spin-gapless ferromagnetic semiconductor of CrGa2Se4 monolayer, in which the type of spin-polarized current can be tuned by tailoring the Fermi energy. Moreover, the magnetic anisotropy energy calculations indicate that the CrGa2Se4 monolayer possesses spin anisotropy both in the basal plane and the vertical plane. This originates from the distortion-induced rearrangement of the 3d electrons in the CrSe6 octahedron and results in an inclined easy axis out of the film. The Curie temperature (Tc) of ferromagnetic phase transition for 2D CrGa2Se4 is more than 200 K. This 2D material shows promising transport properties for spintronics applications and is also important for fundamental research in 2D magnetism.

Amorphous CoFeB films grown on GaAs(001) substrates demonstrating significant in-plane uniaxial magnetic anisotropy were investigated by vector network analyzer ferromagnetic resonance. Distinct in-plane anisotropy of magnetic damping, with a largest maximum-minimum damping ratio of about 109%, was observed via analyzing the frequency dependence of linewidth in a linear manner. As the CoFeB film thickness increases from 3.5 nm to 30 nm, the amorphous structure for all the CoFeB films is maintained while the magnetic damping anisotropy decreases significantly. In order to reveal the inherent mechanism responsible for the anisotropic magnetic damping, studies on time-resolved magneto-optical Kerr effect and high resolution transmission electron microscopy were performed. Those results indicate that the in-plane angular dependent anisotropic damping mainly originates from two-magnon scattering, while the Gilbert damping keeps almost unchanged.

Using the vibrating sample magnetometer and ex situ vector network analyzer ferromagnetic resonance, the static and dynamic magnetic properties of Tb (4 nm)/Cr ( t Cr )/Ni 80 Fe 20 (12 nm) trilayers with different thickness of Cr layer (from 0.2 to 4.0 nm) were investigated comparing with those of Ni 80 Fe 20 film. From the results of in-plane static magnetic hysteresis loops, we analyzed the soft magnetic properties and in-plane anisotropy, along with obtaining the saturation magnetization ( M s ) which shows no obvious reducing and a modulation akin to RKKY coupling. By fitting the relationship of resonance field and linewidth versus resonance frequency, the effective magnetization 4π M eff , gyromagnetic ratio γ , and effective damping coefficient ( α eff ) were extracted. It is worthwhile to mention that the inserting of ultrathin Cr layer (0.2 nm) enhanced the above parameters obviously, which then backed down towards their values in Ni 80 Fe 20 film with increasing the thickness of Cr layer as a result of the weakening magnetic proximity effect and the decreasing spin-pumping effect in trilayers. Finally, they became flattening with the Cr layer thicker than 1 nm where oscillations are also observed in the value of γ and α eff. Interestingly, the oscillations in α eff and γ are consistent with each other, which implies the damping mechanism mainly related to the spin-orbit coupling originating from the indirect interaction between Tb and Ni 80 Fe 20 . In addition, the inhomogeneous broadening (Δ H 0 ) were determined to be very small which further ascertain the accurate of the α eff .

A 3.5 nm amorphous CoFeB film was sputtered on GaAs (001) wafer substrate without applying magnetic field during deposition, and a significant in-plane uniaxial magnetic anisotropy (UMA) field (Hu) of about 300 Oe could be achieved. To precisely determine the intrinsic Gilbert damping constant (α) of this film, both ferromagnetic resonance (FMR) and time-resolved magneto-optical Kerr effect (TRMOKE) techniques were utilized. With good fitting of the dynamic spectra of FMR and TRMOKE, α is calculated to be 0.010 and 0.013, respectively. Obviously, the latter is 30% larger than the former, which is due to the transient heating effect during the TRMOKE measurement. In comparison with ordinary amorphous CoFeB films with negligible magnetic anisotropies, α is enhanced significantly in the CoFeB/GaAs(001) film, which may be mainly resulted from the enhanced spin-orbit coupling induced by the CoFeB/GaAs interface. However, the significant in-plane UMA plays minor role in the enhancement of α.

Single-crystal Fe dot arrays with the lateral size varying from 400 nm to 50 nm are fabricated by focused ion beam (FIB) direct writing from a single-crystalline 10 monolayer (ML) Fe (100) continuous thin film grown on GaAs substrate. The Kerr hysteresis loops of both dot arrays and continuous thin film are measured by focused magnetooptical Kerr effect (MOKE) measurements along four major crystal directions: [0-11] [010] [011] and [001]. It is found that the in-plane uniaxial anisotropy has been greatly reduced down to zero in the dot arrays when the size is less than 150 nm. The micromagnetic simulations confirm the reduction of this intrinsic in-plane uniaxial anisotropy in the patterned dots by separating the effect of the shape anisotropy. The experimental and simulation results further indicate an additional magnetic uniaxial anisotropy along the [010] direction.

Magnetic anisotropies of Fe/MgO/GaAs(100) hybrid structure with two different nonmagnetic capping materials, Au and MgO have been studied by ferromagnetic resonance (FMR). A uniaxial anisotropy, unexpected from the crystal structure was observed in the ultrathin films for both capping materials. Its global easy axis is along [0-11] direction while two (010) directions are equally magnetic hard regardless of the overlayer material. The in-plane uniaxial anisotropy (in-plane cubic anisotropy) of the Au capped samples is stronger (weaker) than that of the MgO capped ones within the range of t Fe = 7.1 to 28 ML. This suggests that the MgO overlayer suppresses the uniaxial anisotropy faster than the Au overlayer.

The magnetic anisotropies are one of the dominating factors affecting the behavior of magnetic materials, which is profoundly evident in magnetic ultrathin films, and significant in the application of information storage and magnetic sensor field. Extensive studies of magnetic anisotropies in various films have been carried out. It is well known that the contribution of magnetocrystalline anisotropy is negligible in isotropic polycrystalline films while essential in single-crystal films. However, in textured film, a polycrystalline film composed of nanograins with the near same lattice orientation, the competing interactions between magnetocrystalline and other anisotropy is still an open issue. The quantitative investigations on the contribution of magnetocrystalline anisotropy in the textured film are rarely reported. In this paper, the expression of magnetocrystalline anisotropy energy in textured film (texture anisotropy energy) is given, and angle-resolved FMR studies on the textured Fe 3 O 4 film is also presented.

Using micromagnetic simulation, we investigate the current-induced multiple domain wall motion (CIDWM) in zigzag nanowires with different bar angles (θ=90°, 120° and 150°). Two dynamic processes of single DWM and double DWM are found in different regimes of current density identified by two thresholds in all zigzag nanowires. The decreasing threshold current is found in the zigzag nanowires with increased bar angles, indicating the angular-dependence of the magnetic pinning. This work suggests a possibility of manipulating the single/multiple DWM in future DW devices by introducing the shape anisotropy.

This letter reports a free energy density model for textured films in which the related physical concept and expression of magneto-texture anisotropy energy are presented. The structural characterization and out-of-plane angular dependence ferromagnetic resonance of strongly textured Fe3O4 films were systematically investigated. We found that the typical free energy density model for polycrystalline film cannot be applied to the textured films. With the introduction of magneto-texture anisotropy energy in the free energy density model for thin films, we simulated and quantitatively determined the competing anisotropies in (111)-textured Fe3O4 films.

Previous studies on epitaxial Fe3O4 rings in the context of spin-transfer torque effect have revealed complicated and undesirable domain structures, attributed to the intrinsic fourfold magnetocrystalline anisotropy in the ferrite. In this Letter, we report a viable solution to this problem, utilizing a 6-nm-thick epitaxial Fe3O4 thin film on GaAs(100), where the fourfold magnetocrystalline anisotropy is negligible. We demonstrate that in the Fe3O4 planar wires patterned from our thin film, such a unique magnetic anisotropy system has been preserved, and relatively simple magnetic domain configurations compared to those previous reports can be obtained.

CoNiFe patterned films with rectangular elements, all 600-nm wide but of different lengths, were fabricated and investigated by ferromagnetic resonance experiment and micromagnetic simulation. An in-plane magnetic uniaxial anisotropy was exhibited, and its value increases with the increase of the aspect ratio of the elements, which was fitted by the model, including a quasi-ellipsoid demagnetizing field and a non-uniform demagnetizing field. The relative importance of the non-uniform demagnetizing field decreased from 0.26 to 0.16 with the increase of the length—width aspect ratio of the patterned element from 1.5 to 10. The demagnetizing factors in the three principal axes were determined from the experimental data of ferromagnetic resonance, which agreed reasonably well with the values calculated by micromagnetic simulation. The calculation also indicated that the interaction between elements could be neglected when the edge-to-edge spacing between neighboring elements was larger than 3 μm in our patterned films.

The evolution of both in-plane and out-of-plane magnetic anisotropies has been studied on different thicknesses of Fe3O4/InAs(100) hybrid spintronic structures by ferromagnetic resonance. The uniaxial magnetic anisotropy with easy axis along InAs [011] direction and hard axis along [0-11] direction and the cubic magnetic anisotropy are determined by fitting the resonance field. The cubic magnetic anisotropy constant K1 is negative, as that of bulk magnetite, and its absolute value increases rapidly from 0.2 × 104 erg/cm3 to 10.8 × 104 erg/cm3 with increasing thickness of Fe3O4 film. When the thickness of Fe3O4 film is only several monolayers (tFe = 6 nm), a bulk-like cubic magneto-crystalline anisotropy is built up. The uniaxial anisotropy constant is much smaller than that in Fe3O4/GaAs film with the same thickness of Fe3O4 film, as expected from the less lattice mismatch at the interface.

The structure and magnetic properties of Fe1−xGd(Tb)x films prepared by sputtering have been investigated using x-ray diffraction, vibrating sample magnetometer, and ferromagnetic resonance. Magnetic measurements show that the saturation magnetization decreases as the increase of Gd(Tb) content, which agrees with that Gd(Tb) atomic moments align antiparallel with Fe moments. Theoretical fittings of the angular dependence of ferromagnetic resonance field yield the second- and forth-order perpendicular anisotropy constants K⊥1 and K⊥2, which show a spin reorientation with increasing Gd(Tb) doping. The intrinsic contribution of ferromagnetic resonance linewidth as a result of Gilbert damping is separated from the extrinsic contribution because of the inhomogeneity of the films. It is found that the additions of Gd additives do not significantly improve the damping constant, whereas the Tb dopants increase the damping constant from 0.04 without Tb to 0.11 with 19% Tb, thus a remarkable enhancement of 175%.

The magnetic anisotropy of epitaxial layered structures of Fe3O4(tFe=4nm)∕GaAs(100), MgO(3nm)∕Fe3O4(tFe=4nm)∕GaAs(100), and Fe3O4(tFe=4nm)∕MgO(3nm)∕Fe3O4(tFe=4nm)∕GaAs(100) was studied by ferromagnetic resonance. It was shown that a predominant in-plane uniaxial magnetic anisotropy and a small fourfold cubic magnetocrystalline anisotropy existed. The in-plane uniaxial anisotropy constant decreased when the MgO layer was covered on Fe3O4∕GaAs, while the cubic anisotropy increased. In the sandwich structures, two resonance peaks were observed. One is similar to that in Fe3O4∕GaAs layer, while another corresponding to Fe3O4 on MgO showed more remarkable fourfold anisotropy and lower uniaxial anisotropy due to smaller mismatch between Fe3O4 and MgO. The interface the Fe3O4 layer is deposited on has dominant effect.

Magnetic anisotropies of single crystal ultrathin Fe3O4 films on GaAs(100) have been studied by ferromagnetic resonance (FMR). The dependence of the FMR fields on the field orientation was measured both in plane and out of plane. The ultrathin films show predominantly an in-plane uniaxial magnetic anisotropy with the easy axis along the [0−11] direction of the GaAs substrate. The in-plane uniaxial anisotropy constant decreases with increasing thickness and changes from 7.1×104to2.1×104ergs∕cm3 when the thickness tFe varies from 4to8nm. An in-plane fourfold anisotropy due to cubic magnetocrystalline anisotropy coexists with the uniaxial magnetic anisotropy and increases with increasing film thickness. For tFe=8nm, the cubic anisotropy constant K1 reaches −8.4×104erg∕cm3, which is 76% of the value of bulk spinel Fe3O4. The out-of-plane measurements indicate a negative perpendicular anisotropy in these ultrathin Fe3O4 films.