FMR-related phenomena in spintronic devices

Spintronic devices, such as non-volatile magnetic random access memories and logic devices, have attracted considerable attention as potential candidates for future high efficient data storage and computing technology. In a heavy metal or other emerging material with strong spin-orbit coupling (SOC), the charge currents induce spin currents or spin accumulations via SOC. The generated spin currents can exert spin-orbit torques (SOTs) on an adjacent ferromagnet, which opens up new avenues for realization of magnetization dynamics and switching of the ferromagnetic layer for spintronic devices. In the SOT scheme, the charge-to-spin interconversion efficiency (SOT efficiency) is an important figure of merit for applications. For effective characterization of this efficiency, ferromagnetic resonance (FMR) based methods, such as spin transfer torque ferromagnetic resonance (ST-FMR) and spin pumping, are commonly utilized in addition to low frequency harmonic or DC measurements. In this review, we focus on ST-FMR measurements for the evaluation of the SOT efficiency. We provide a brief summary of the different ST-FMR setups and data analysis methods. We then discuss ST-FMR and SOT studies in various materials, including heavy metals and alloys, topological insulators, two-dimensional (2D) materials, interfaces with a strong Rashba effect, antiferromagnetic materials, 2D electron gas in oxide materials and oxidized nonmagnetic materials.