We systematically investigated the electronic structure of full-Heusler alloys with valence electron counts per formula unit of 24 by using first-principles calculation. We found various semiconducting full-Heusler alloys with flat bands at the bottom of the conduction band. In terms of low toxicity and low cost, we focused on semiconducting Fe2TiSn and Fe2TiSi. We found that they could possess high thermoelectric power ranging from -300 to -160 µV/K with the electron-carrier concentrations from 1×1020 to 1×1021 cm-3 around room temperature. Our results also suggest that Fe2TiSn1-xSix alloy has a great potential to realize a higher figure-of-merit (Z T) value, compared to conventional full-Heusler alloys.

The origin of the magnetism of MnSi 1.7 nanoparticles in Si is investigated using the first-principles calculations: bulk and interface effects are considered. The bulk magnetic property is expected to be affected by stoichiometry, strain, and charge accumulation. Stoichiometry and charge accumulation induce a ferromagnetic state, and strain stabilizes the ferromagnetic state. Another factor, the MnSi 1.7 / Si interface formation, is seen as triggering ferromagnetism strongly localized at the interface. These two mechanisms are shown to be related to the experimentally determined hard and soft components, respectively.

The annealing-temperature (700–900 °C) dependence of the ferromagnetism of manganese-implanted silicon is investigated. In the annealed samples, the manganese-containing nanoparticles, whose mean size was found to get bigger with temperature, are formed and these samples show ferromagnetism. We obtain evidence that the samples annealed at 800–850 °C produce two kinds of ferromagnets and that one of them offers a coercivity as high as 2500 Oe, suggesting the possibility of Si-based nanostructures with stable ferromagnetism. The origin of these ferromagnetisms is also discussed in conjunction with the size distribution of the nanoparticles.

Recent progress in magnetic tunnel junctions (MTJs) with a perpendicular easy axis consisting of CoFeB and MgO stacking structures has shown that magnetization dynamics are induced due to voltage-controlled magnetic anisotropy (VCMA), which will potentially lead to future low-power-consumption information technology. For manipulating magnetizations in MTJs by applying voltage, it is necessary to understand the coupled magnetization motion of two magnetic (recording and reference) layers. In this report, we focus on the magnetization motion of two magnetic layers in MTJs consisting of top layers with an in-plane easy axis and bottom layers with a perpendicular easy axis, both having perpendicular magnetic anisotropy. According to rectified voltage (Vrec) measurements, the amplitude of the magnetization motion depends on the initial angles of the magnetizations with respect to the VCMA direction. Our numerical simulations involving the micromagnetic method based on the Landau-Lifshitz-Gilbert equation of motion indicate that the magnetization motion in both layers is induced by a combination of VCMA and transferred angular momentum, even though the magnetic easy axes of the two layers are different. Our study will lead to the development of voltage-controlled MTJs having perpendicular magnetic anisotropy by controlling the initial angle between magnetizations and VCMA directions.