The search for efficient spin conversion in Bi has attracted great attention in spin-orbitronics. In the present work, we employ spin-torque ferromagnetic resonance to investigate spin conversion in Bi/Ni80Fe20(Py) bilayer films with continuously varying Bi thickness. In contrast with previous studies, sizable spin-transfer torque (i.e., a sizable spin-conversion effect) is observed in Bi/Py bilayer film. Considering the absence of spin conversion in Bi/yttrium-iron-garnet bilayers and the enhancement of spin conversion in Bi-doped Cu, the present results indicate the importance of material combinations to generate substantial spin-conversion effects in Bi.

In-plane magnetization reversal of a permalloy/platinum bilayer was detected using the spin rectification effect. Using a sub-GHz microwave frequency to excite spin-torque ferromagnetic resonance (ST-FMR) in the bilayer induces two discrete DC voltages around an external static magnetic field of 0 mT. These discrete voltages depend on the magnetization directions of the permalloy and enable detection of the in-plane magnetization reversal. The threshold current density for the magnetization reversal is around 10-20 MA/cm², the same order as for known spin-orbit torque (SOT) switching with in-plane magnetization materials. The magnitude of the signal is the same or larger than that of the typical ST-FMR signal; that is, detection of magnetization switching is highly sensitive in spite of deviation from the optimal ST-FMR condition. The proposed method is applicable to a simple device structure even for a small ferromagnetic electrode with a width of 100 nm.

DC voltages via spin rectification effect (SRE), VDC, under microwave irradiation are investigated for three platinum (Pt)/ferromagnetic metal (FM) bilayer structures: Pt/Ni80Fe20, Pt/Co, and Pt/Fe. At the microwave frequency region lower than the resonant frequency, large VDC is obtained at zero DC magnetic field for all devices. In frequency dependence just around the resonant frequency, sharp rise and drop of magnitude in VDC are observed. These behaviors are well explained by the numerically calculated magnetic susceptibility. It is also found that the magnitude of VDC is strongly dependent on the slope of magnetoresistance spectrum. These findings lead to developments of sensitive detection technique for nano-scale magnetization switching.

While the effective g -factor can be anisotropic due to the spin-orbit interaction (SOI), its existence in solids cannot be simply asserted from a band structure, which hinders progress on studies from such viewpoints. The effective g -factor in bismuth (Bi) is largely anisotropic; especially for holes at T -point, the effective g -factor perpendicular to the trigonal axis is negligibly small (<0.112), whereas the effective g -factor along the trigonal axis is very large (62.7). We clarified in this work that the large anisotropy of effective g -factor gives rise to the large spin conversion anisotropy in Bi from experimental and theoretical approaches. Spin-torque ferromagnetic resonance was applied to estimate the spin conversion efficiency in rhombohedral (110) Bi to be 17 to 27%, which is unlike the negligibly small efficiency in Bi(111). Harmonic Hall measurements support the large spin conversion efficiency in Bi(110). A large spin conversion anisotropy as the clear manifestation of the anisotropy of the effective g -factor is observed. Beyond the emblematic case of Bi, our study unveiled the significance of the effective g -factor anisotropy in condensed-matter physics and can pave a pathway toward establishing novel spin physics under g -factor control.