Among different physical parameters taken into account for practical implementations in the field of spin-based electronics (spintronics), magnetocrystalline anisotropy (MCA) and spin polarization play a particularly important role. The former determines the orientation of magnetization direction, while a high degree of the latter is required for producing a spin-polarized current, a cornerstone of spintronics. Due to the miniaturization of the modern electronic devices, one often needs to consider physical effects associated with reduced geometry. In particular, in magnetic thin-film materials, MCA may take a form of perpendicular magnetic anisotropy (PMA), which could be beneficial, e.g. in magnetoresistive random-access memory (MRAM). Yet, combining PMA with half-metallicity may be a challenging task, since the latter is usually destroyed in thin-film geometry (e.g., due to the emergence of surface states), while the former is most pronounced in reduced geometry, because of the contribution to MCA from surface anisotropy. Here, we theoretically explore the nature of PMA in the thin-film full Heusler alloy Co 2 MnSi. This material was extensively studied in the past, and it is one of the first compounds for which a half-metallic electronic structure was experimentally confirmed. In addition, it has been reported that this alloy may exhibit perpendicular magnetic anisotropy in thin-film geometry. Here, by analyzing the site-projected magnetocrystalline anisotropy energy (MAE), we confirm that both PMA and surface half-metallicity are very sensitive to the termination surface and mechanical strain. In particular, while MnSi-termination under compressive strain may retain both 100% spin-polarization and out-of-plane magnetization orientation, Co-termination has a detrimental impact on both. These results may serve as a guide for practical applications in the field of spin-based electronics.
We have carried out a combined theoretical and experimental investigation of both stoichiometric and nonstoichiometric CoFeVGe alloys. In particular, we have investigated CoFeVGe, Co1.25Fe0.75VGe, Co0.75Fe1.25VGe, and CoFe0.75VGe bulk alloys. Our first principles calculations suggest that all four alloys show ferromagnetic order, where CoFeVGe, Co1.25Fe0.75VGe, and Co0.75Fe1.25VGe are highly spin polarized with spin polarization values of over 80%. However, the spin polarization value of CoFe0.75VGe is only about 60%. We have synthesized all four samples using arc melting and high-vacuum annealing at 600 °C for 48 hours. The room temperature x-ray diffraction of these samples exhibits a cubic crystal structure with disorder. All the samples show single magnetic transitions at their Curie temperatures, where the Curie temperature and high field (3T) magnetization are 288 K and 42 emu/g; 305 K and 1.5 emu/g; 238 K and 39 emu/g; and 306 K and 35 emu/g for CoFeVGe, Co1.25Fe0.75VGe, Co0.75Fe1.25VGe, and CoFe0.75VGe, respectively.
Metal/transition metal dichalcogenide interfaces are the subject of active research, in part because they provide various possibilities for interplay of electronic and magnetic properties with potential device applications. Here, we present results of our first principles calculations of nearly strain-free Ni/WSe 2 and Ni/MoS 2 interfaces in thin-film geometry. It is shown that while both the WSe 2 and MoS 2 layers adjacent to Ni undergo metallic transition, the layers farther from the interface remain semiconducting. In addition, a moderate value of spin-polarization is induced on interfacial WSe 2 and MoS 2 layers. At the same time, the electronic and magnetic properties of Ni are nearly unaffected by the presence of WSe 2 and MoS 2 , except a small reduction of magnetic moment at the interfacial Ni atoms. These results can be used as a reference for experimental efforts on epitaxial metal/transition metal dichalcogenide heterostructures, with potential application in modern magnetic storage devices.
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