Effect of Tilted Magnetic Anisotropy on the Deterministic Current-Induced Magnetization Reversal in Quasi-Perpendicularly Magnetized Ta/Pt/CoFeB/Pt Multilayers

Abstract

Deterministic current-induced magnetization reversal is observed in quasi-perpendicularly magnetized Ta/Pt/CoFeB/Pt multilayer thin films without the assistance of an in-plane field. In a quasi-perpendicularly magnetized system, the anisotropy is tilted slightly away from the normal to the film plane. This tilt in the anisotropy is obtained by growing the films in an oblique-angle sputter deposition technique, which results in a gradient in the thickness of the layers. To estimate the tilt, out-of-plane hysteresis loop measurements are performed in the presence of an in-plane bias field. The effect of the tilt is reflected in the shift in the hysteresis loop. A measurement of this shift at different relative azimuthal orientations of the in-plane projection of the tilt direction with respect to the in-plane bias field direction gives a tilt of 0.74° (±0.06°) in Ta(3 nm)Pt(3 nm)CoFeB(0.5 nm)Pt(1 nm) with all the layers having a thickness gradient. In addition, field-induced domain wall velocity measurements in the creep regime on Ta(3 nm)Pt(3 nm)CoFeB(0.5 nm)Pt(1 nm) thin film with a thickness gradient only in CoFeB layer give an elliptical profile for the domain wall. In the current-induced magnetization reversal studies, threshold current density of $1.06 \times 10^{11}$ Am−2 is required to deterministically switch the device fabricated from Ta(3 nm)Pt(3 nm)CoFeB(0.5 nm)Pt(1 nm) thin film with all the layers having a thickness gradient. On application of in-plane bias, there is a shift in the threshold current densities given by $2.6 \times 10^{8}$ Am−2 of in-plane bias field.