A high degree of spin polarization in electron transport is one of the most sought-after properties of a material which can be used in spintronics—an emerging technology utilizing a spin degree of freedom in electronic devices. An ideal candidate to exhibit highly spin-polarized current would be a room temperature half-metal, a material which behaves as an insulator for one spin channel and as a conductor for the other spin channel. In this paper, we explore a semi-Heusler compound, IrMnSb, which has been reported to exhibit pressure induced half-metallic transition. We confirm that the bulk IrMnSb is a spin-polarized metal, with dominant contribution to electronic states at the Fermi energy from majority-spin electrons. Application of a uniform pressure shifts the Fermi level into the minority-spin energy gap, thus demonstrating pressure induced half-metallic transition. This behavior is explained by the reduction of the exchange splitting of the spin bands consistent with the Stoner model for itinerant magnetism. We find that the half-metallic transition is suppressed when instead of uniform pressure the bulk IrMnSb is exposed to biaxial strain. This suppression of half-metallicity is driven by the epitaxial strain induced tetragonal distortion, which lifts the degeneracy of the Mn 3 d t _2g and e _g orbitals and reduces the minority-spin band gap under compressive strain, thus preventing half-metallic transition. Our calculations also indicate that in thin film geometry, surface states emerge in the minority-spin band gap, which has detrimental for practical applications impact on the spin polarization of IrMnSb.

We performed combined theoretical and experimental studies of electronic, structural, and magnetic properties of Fe₂MnSn Heusler alloy. The density functional theory calculation shows that the Fe₂MnSn alloy has two energetically close phases, namely, hexagonal D0₁₉ and cubic L2₁, which agrees well with the experimental results. Both the hexagonal and cubic phases are ferromagnetic, with large magnetization values of about 6 μ_B/f.u. and high Curie temperature above room temperature. The hexagonal phase shows high magnetic anisotropy of 5.1 Merg/cm³. These findings may be interesting for magnetic applications where large saturation magnetization, high Curie temperature, and high magnetic anisotropy are desired.

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.

Half-metals with high Curie temperature are ideal candidates for applications in spin-based electronics—an emerging technology utilizing a spin degree of freedom in electronic devices. Many half-metallic materials have been predicted theoretically, and some have been confirmed experimentally. At the same time, in thin-film geometry the electronic structure of these materials may change due to the potential presence of surface/interface states. This could limit practical applications of these materials in nano-size devices, since typically these states result in reduced spin-polarization. Here, from first principles we study a full Heusler compound, Co ₂ CrAl in thin film geometry. This material has been studied extensively, and it has been reported that it exhibits half-metallic properties in the bulk. We show contrary to the earlier reports that this material retains 100% spin polarization in CrAl-terminated thin film geometry (Co-termination results in destroyed half-metallicity). Moreover, we confirm that under biaxial strain Co ₂ CrAl retains half-metallicity for a practically feasible range of considered pressure, i.e. in principle it may stay half-metallic if used in thin-film heterostructures, where lattice mismatch is a common scenario. The magnetic alignment of Co ₂ CrAl is confirmed to be ferromagnetic, with the non-integer total magnetic moment of Co-terminated cell, and the integer total magnetic moment of CrAl-terminated cell, consistent with their corresponding non-half-metallic and half-metallic electronic structures. If confirmed experimentally, these results may have an important impact in spin-based electronics.

Magnetocrystalline anisotropy (MCA) is one of the key parameters investigated in spin-based electronics (spintronics), e.g. for memory applications. Here, we employ first-principles calculations to study MCA in thin film full Heusler alloy Co ₂ CrAl. This material was studied in the past, and has been reported to exhibit half-metallic electronic structure in bulk geometry. In our recent work, we showed that it retains a 100% spin-polarization in thin-film geometry, at CrAl atomic surface termination. Here, we show that the same termination results in a perpendicular magnetic anisotropy, while Co surface termination not only destroys the half-metallicity, but also results in in-plane magnetization orientation. In addition, for films thicker than around 20 nm the contribution from magnetic shape anisotropy may become decisive, resulting in in-plane magnetization orientation. To the best of our knowledge, this is one of the first reports of half-metallic thin-film surfaces with perpendicular magnetic anisotropy. This result may be of interest for potential nano-device applications, and may stimulate a further experimental study of this and similar materials.