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Anomalous Nernst effect of epitaxial Fe4− xNi xN films on MgAl2O4(001) substrates was characterized. The Ni/Fe ratio ( x) in Fe4− xNi xN films was changed in the range of 0 ≤ x ≤ 2.8, and the Fe4− xNi xN phase started to decompose into FeNi at about x = 2.2. The anomalous Nernst coefficient ( SANE) decreased with x from 1.7 to 0.6 μV/K and the Seebeck coefficient increased with x from −2.3 to 1.2 μV/K. The transverse thermoelectric conductivity ( αxy) evaluated from the experimental data showed a decrease with x and the change of αxy dominated the change of SANE. The anomalous Hall conductivity and αxy of Fe4N and Fe2.8Ni1.2N were obtained by first-principles calculations, showing a significant difference from the experimental results, which might be caused by the contribution from the extrinsic mechanisms.

Electric control of magnetism has been a topic of interest for various spintronic applications. It is known that monoatomic Pt layer insertion at the Fe/MgO interface increases voltage-controlled magnetic anisotropy (VCMA). However, the reason for the optimality of this thickness has not been explained thus far. In this study, we observed the changes in the electronic states at the Fe/MgO interface using tunneling spectroscopy on an epitaxial Fe(001)/Pt/MgO(001) structure to characterize the density of states around the Fermi level. We found that a surface resonant state is formed at the Fermi level by the insertion of a monoatomic Pt layer, which is consistent with our first principles study. In addition, the VCMA enhancement owing to the formation of this surface resonance state agrees with the recently proposed microscopic theory.

Tunnel magnetoresistance (TMR) in MgO-based magnetic tunnel junctions (MTJs) with equiatomic quaternary CoFeMnSi Heusler and CoFe alloy electrodes is studied. The epitaxial MTJ stacking structures were prepared using ultrahigh-vacuum magnetron sputtering, where the CoFeMnSi electrode has a full B2 and partial L21 ordering crystal structure. Maximum TMR ratios of 101% and 521% were observed at room temperature and 10 K, respectively, for the MTJs. The large bias voltage dependence of the TMR ratio was also observed at low temperature (LT), as similarly observed in Co2MnSi Heusler alloy-based MTJs in the past. The physical origins of this relatively large TMR ratio at LT were discussed in terms of the half-metallicity of CoFeMnSi.

We have performed high-resolution angle-resolved photoemission spectroscopy of oxygen-adsorbed Fe thin films on W(110) to elucidate the evolution of electronic states upon surface oxidation. After oxygen adsorption of 0.25 monolayer onto Fe films, we found a surface state in the vicinity of the Fermi level which exhibits an undulating energy band dispersion. Our first-principles band-structure calculation indicates that this state is attributed to the spin-polarized minority band arising from the hybridization between Fe 3d and O 2p orbitals. The present result suggests that the observed surface state is related to the unusual magnetic properties of oxidized Fe surfaces.

We study the spin and orbital magnetic moments in Ta/Co0.4Fe0.4B0.2/MgO by x-ray magnetic circular dichroism measurements as well as first-principles calculations, in order to clarify the origin of the perpendicular magnetic anisotropy. Both experimental and theoretical results show that orbital magnetic moment of Fe is more anisotropic than that of Co with respect to the magnetization direction. The anisotropy is larger for thinner CoFeB, indicating that Fe atoms at the interface with MgO contribute more than Co to the observed perpendicular magnetic anisotropy.

We report ultrahigh-resolution spin-resolved hard X-ray photoemission (HAXPES) for a buried FeNi alloy film. By utilizing the forward Mott scattering in a Au layer on FeNi, our spin-resolved HAXPES method does not require a standard spin detector and allows us to use the multi-channel electron detection system for the high-efficient electron detection as used in conventional photoemission spectroscopy. A combination of the forward Mott scattering and multi-channel detection leads us to measure a clear spin polarization as well as spin-resolved majority and minority states in the Fe 2p core-level spectra without using the standard spin detector. This method enables us to measure spin-resolved core-level spectra for buried ferromagnetic materials.

Magnetocrystalline anisotropy (MCA) of Fe(001) interfaces with various non-magnetic metals (Hf, Zr, Ti, Ta, Nb, V, Ir, Rh, Pt, Pd, Au, Ag, Cu, and Zn) was investigated by first-principles calculations. We found that Fe interfaces with non-magnetic metals with fully occupied d states tend to show perpendicular MCA. The spin-orbit coupling in interfacial Fe atoms plays an important role in perpendicular MCA. Conversely, Fe interfaces with non-magnetic metals with partially occupied d states exhibit in-plane MCA. The Hf/Fe(001) interface shows an exceptionally large perpendicular MCA energy of 1.5 mJ/m2, which corresponds to that of the MgO/Fe(001) interface. In these cases, contributions from interfacial Fe atoms to MCA are relatively small, and the large spin-orbit coupling of non-magnetic atoms is the primary contribution to MCA. We conclude that formation of Hf/Fe(001) interfaces will enhance the perpendicular magnetization of MgO/CoFeB-based magnetic tunnel junctions.

We have investigated the electric field (EF) effect on the magnetic anisotropy energy (MAE) in the thin films MgO/M/Fe/Au(001) and MgO/Fe/M(001) (M = Pd, Pt, and Au) by means of first-principles density-functional calculations. We find that the MAE varies linearly with the EF and investigate the change in slope of the MAE as a function of the EF as the buffer layer is changed. We find that a single monatomic buffer layer may be useful for devices that use EF-modified MAE. We simulate the critical EF for easy-axis rotation and discuss interface effects of Mg/Fe and Fe/Au on MAE.

We have investigated the electric field (EF) effect on the magnetic anisotropy energy (MAE) in thin films MgO/Fe/M(001) (M = Au and Pt) by means of first-principles density-functional calculations. The EF dependence of the MAE is enhanced significantly in the film with the Pt substrate compared to that with the Au substrate. This enhancement is attributed to the EF-induced hybridization between Fe 3d- and Pt 5d-orbitals. This implies that the Pt layer stacked on the magnetic layer strengthens the sensitivity of devices for bias-voltage-induced magnetic control.