Influence of ferrimagnetic structures on the spin-orbit torque efficiency

Abstract

Magnetic film, consisting of transition metal(TM) and rare earth(RE) material, has ferrimagnetic properties through the anti-ferromagnetic coupling in each other elements. Due to this, TM-RE film shows potential to replace the conventional ferromagnetic film in information memory device using spin orbit torque(SOT ) with the fast domain wall motion, longer spin coherent length, and bulk perpendicular anisotropy properties. In this paper, the difference of spin orbit torque and magnetic properties in alloy and multilayer CoFe-Tb structure are studied using vibrating sample magnetometer(VSM) and harmonic measurement. The Ta/Pt/CoFe0.74Tb0.26/Cu/Ta and Ta/Pt/[CoFe/Tb]N/Cu/Ta stacks are deposited for this experiment. In both alloy and multilayered group has same 1.2nm, 1.8nm, 2.4nm thick CoFe-Tb layer and same composition to control the other unintended influence. In magnetic properties, all of multilayer group shows grater magnetization and coercivity. However, in spin hall angle, alloy group shows spin hall angle increasing with the thickness increase, whereas multilayer group shows decreasing. This result indicate that multilayer structure has more hard magnetic properties but unfavorable to spin orbit torque efficiency.