Study of Al interdiffusion in ultrathin beta-Ta/Co2FeAl/MgO heterostructures for enhanced spin-orbit torque

Abstract

In this work perpendicular magnetization of Co2FeAl (CFA) full-Heusler alloy films is achieved using rapid thermal annealing under N-2/H-2 gas flow in Si/beta-Ta(6.5 nm)/CFA(0.6-2 nm)/MgO(1.15 nm)/Pd(1 nm) heterostructures. The Al interdiffusion into MgO layer plays an important role in determining perpendicular magnetic anisotropy(PMA) and increasing the damping constant (alpha) of ultrathin CFA samples. The time of flight SIMS depth profiling along with XPS is used to study interdiffusion of Al across CFA/MgO interface. XPS analysis of Al-2p and Mg-1s spectra indicate the formation of A1(2)O(3) and MgAl2Ox oxide phases at CFA/MgO interface in addition to pure Al metal. The Slonczewski-like and the field-like SOT effective fields are quantified using second harmonics measurements. An effective spin hall angle of beta-Ta (6.5 nm) is estimated in range - 0.02 to - 0.06 for CFA layer thickness varied from 0.8 nm to 1.5 nm.