Effective damping constant and perpendicular anisotropy of GdFeCo / TbFe exchange coupled bilayer

Abstract

Spin transfer torque (STT) switching is considered as a promising technology to realize Gbit class magnetic random access memories (MRAMs). However, to develop high density MRAM with densities of several Gbit and beyond, there still remains a challenge to reduce critical current density for the STT switching while keeping large thermal stability of the memory layer. One of the solutions for this challenge is thermally assisted MRAM in which the memory layer is heated during the writing. We have studied amorphous GdFeCo and GdFeCo / TbFe exchange coupled bilayer as memory layers of the thermally assisted MRAM cell, and reported the STT switching of these memory layer [1-3]. In this study, we report Gilbert damping constant a and perpendicular anisotropy of GdFeCo / TbFe exchange coupled bilayer, and compare these data with critical current densities Jc. of the STT switching of GdFeCo / TbFe memory layers.