Raising the thermoelectric voltage in spin thermoelectric generators is an important subject. We investigated the substitution of bismuth for yttrium to increase spin pumping at the paramagnetic metal and ferrimagnetic insulator (PM/FMI) interface, and tested bismuth-substituted iron garnet films grown by liquid phase epitaxy. Epitaxial Bi-substituted iron garnet films exhibit large growth-induced magnetic anisotropy perpendicular to the film surface. This anisotropy increases the magnetic damping α in the FMI; α also increases with increasing Bi content. We report the rise in voltage observed in a spin thermoelectric generator incorporating Bi-substituted YIG films grown by liquid phase epitaxy, and explain the origin of the voltage rise based on the results of FMR measurements.

A spin-thermoelectric (STE) voltage is generated when a temperature gradient ∇T is applied to an element having a thin Pt layer coated on a magnetic substance. In this study, yttrium iron garnet (YIG) ferrimagnetic films prepared by liquid phase epitaxy (LPE) were tested as magnetic insulators. In addition, polycrystalline YIG slabs were tested to compare the STE voltages of film and slab samples. In a Pt coating and YIG film bilayer structure made by an ultrathin Pt layer of 1-4 nm thickness and an LPE film of approximately 10 µm thickness, a large STE voltage of 600 µV was observed at a probe distance of 5 mm with a temperature difference ∆T of 30 K. On the other hand, the STE voltage of a Pt layer and YIG slab bilayer structure was 340 µV, which is roughly half of that of the Pt/YIG-film element. The cause of the large voltage observed experimentally for the longitudinal spin Seebeck effect element incorporating an LPE YIG film was discussed mainly from the viewpoint of the Pt layer resistivity and the effects of YIG specimen surface conditions on crystallinity and the magnetization process.

A spin thermoelectric (STE) generator is composed of a thin paramagnetic metal (PM) layer, ferrimagnetic insulator (FMI) and PM/FMI bilayer interface. Various studies have been carried out on improving the characteristics of each part of this structure in order to raise the STE voltage $V_{\mathrm {STE}}$ . We investigated the substitution of bismuth for yttrium and aluminum for iron to observe the characteristic changes in $V_{\mathrm {STE}}$ . FMI films of epitaxial Bi-substituted iron garnets exhibit large growth-induced magnetic anisotropy perpendicular to the film surface. This anisotropy increases the magnetic damping $\alpha $ in the FMI, and the values of $\alpha $ increase with increasing Bi content. As a result, a large rise in STE voltage was observed. We report the rise in $V_{\mathrm {STE}}$ observed in an STE generator incorporating Bi-substituted yttrium iron garnet (YIG) films grown by liquid phase epitaxy (LPE) and explain the origin of the voltage rise based on the results of ferromagnetic resonance measurements. To comprehensively examine the effect of substitution on LPE YIG films, the $V_{\mathrm {STE}}$ values observed in STE generators incorporating Al-substituted YIG films are also presented.

The magneto-optical properties of pseudo-quaternary magnetic semiconductor CdMnCoTe films deposited on quartz glass substrates by using molecular beam epitaxy (MBE) equipment were studied in the visible wavelength region at room temperature. The deposition was carried out at an average rate of ∼1 Å/sec for 8 h by using a 4-N Co target sputtered by an electron gun with an emission current of 20 mA, a 5-N CdTe effusion cell heated to 490 °C, and a 4-N MnTe cell heated at 1020 °C. Using this system, we prepared ∼2-µm-thick CdMnTe and CdMnCoTe films on 0.5-mm-thick quartz glass substrates. These films exhibited a preferred (111) growth and paramagnetic characteristics. The magnetization intensities at 15 kOe and room temperature of the two films were similar; approximately 2.5 × 10⁻⁴ emu for the Cd_0.65Mn_0.35Te film and 2.8 × 10⁻⁴ emu for the Cd_0.56Mn_0.39Co_0.05Te film. The Faraday rotation measured at 620 nm in the CdMnCoTe film was −0.32 deg/cm-G, and that in the CdMnTe film was −0.10 deg/cm-G. The Faraday rotation was significantly enhanced in the CdMnCoTe films. Direct ac Faraday rotation observations of the films were successfully performed under 1.27-kHz ac fields generated by using a ring magnet.

Building upon the room-temperature magneto-optical properties of ternary and quaternary zinc blende magnetic semiconductor films of CdMnTe, CdMnCoTe, ZnMnTe, and ZnMnSe reported to date, the present study examines the crystallographic and optical properties of Mn-substituted II-VI based magnetic semiconductor films synthesized on sapphire (SA) or quartz glass (QG) substrates by molecular beam epitaxy. CdTe-based films on sapphire or glass exhibited preferential (111) growth as reported previously. However, ZnTe-based films on sapphire showed a (220) growth believed to be induced by the ₍₂₀₂₎ plane of C-cut hexagonal SA substrates. The influence of crystallinity on optical or magneto-optical properties on both SA and QG is discussed from the viewpoint of the extinction ratio. The extinction ratio of films on QG was low compared to that of films on SA, and decreased further under an applied field. It has been shown that the decrease in the extinction ratio upon the application of a magnetic field contributes to the magneto-optical effect in the films.