Current induced magnetization switching (CIMS) has attracted considerable attention as a new technique for switching the magnetization in magnetic random access memories (MRAMs). Particularly, two types of current-induced magnetization switching are drawn significant attention, namely, spin transfer torque (STT) and spin orbit torque (SOT), which are schematically illustrated in Fig. 1. In STT switching, spin-polarized current is injected into magnetic layer, and angular momentum of the spin-polarized current is transferred to magnetization to reverse its orientation. In SOT switching, electric current is passed through heavy metal layer to produce spin current which is injected to reverse the magnetization. SOT switching is considered to be about 10 times faster than STT at same power consumption, and for SOT switching, electric current does not pass directly through magnetic layer during write operations; therefore, different current paths can be used for read and write resulting in low read disturb faults.
    Our group has studied about the CIMS of the devices with the amorphous heavy rare earth - transition metal (HRE-TM) alloys aiming it for the application to the high density MRAM. HRE-TM are ferrimagnetic materials, where HRE and TM moments are coupled antiparallel each other, and HRE-TM are known to exhibit a large perpendicular magnetic anisotropy and the magnetic properties and Curie temperature are easily controlled by the composition.
    Fig. 2 shows the SOT switching confirmed by flowing a current density about 5 MA/cm² into the Hall bar. The HRE and TM compositional dependences of the SOT as well as the temperature dependence should be studied.