Spin torque-induced magnetization dynamics in giant magnetoresistance devices with Heusler alloy layers

We studied the spin torque-induced magnetization dynamics of full-Heusler Co2(Fe,Mn)Si (CFMS) layers in current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) devices, and obtained the phase diagrams of spin torque-induced phenomena such as magnetization switching and spin torque oscillation. For a device with a 3 nm-thick CFMS free layer and a 20 nm-thick CFMS fixed layer, spin torque oscillation was induced in the free layer magnetization. As the free layer thickness was increased from 3 to 7 nm, on the other hand, the magnetization dynamics were remarkably changed. A 7 nm-thick CFMS free layer showed no clear spin torque oscillation even though it showed the reversible magnetization switching. On the contrary, the magnetization in the 20 nm-thick CFMS fixed layer oscillated at a certain condition. This spin torque-induced instability in the fixed layer magnetization is attributable to the increase in the free layer thickness, the structure of the fixed layer having the extended film, and the stray field coupling between the free and the fixed layers.