Spin orbit coupling (SOC) plays a fundamental role in modern spintronics. Applying a current to materials with large SOC induces a spin current, which can diffuse into a nearby ferromagnet layer and exert torque on the magnetization. Current induced magnetization switching, precession, and domain wall motion have been observed in thin film heterostructures that consist of heavy metals with a large SOC and ferromagnetic materials. Although the device architecture is different from that of a conventional magnetic tunnel junction memory cell in magnetic random access memory (MRAM), the unique characteristics of such spin-orbit-driven magnetization control has triggered significant effort on developing next-generation MRAM technology. Here, we discuss the basics of spin-orbitdriven magnetization control and review experimental means of studying spin orbit torque, i.e., the efficiency of controlling magnetization with currents via the SOC. As new phenomena are being discovered rapidly in this fast evolving field, the aim of this review is to provide an intuitive picture of the methods used to characterize spin orbit torque with the current understanding of the related physics.
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