Observation of higher-order contribution to anisotropic magnetoresistance of thin Pt/[Co/Pt] multilayered films

We studied the magnetoresistance mechanisms in a Pt/[Co/Pt]x5 film consisting of a ferromagnetic [Co/Pt]x5 layer with strong perpendicular magnetic anisotropy and a nonmagnetic Pt layer with strong spin-orbit coupling. We revealed two competing contributions of the sin2 theta and cos4 theta types to its angular and magnetic field de-pendences of electrical resistance at T = 10-250 K corresponding to the out-of-plane rotation of the magneti-zation M(theta) perpendicularly to the electric current. They were attributed to different magnetoresistance mechanisms. The higher-order cos4 theta contribution, which emerges and increases with decreasing temperature, is attributed to the anisotropic magnetoresistance of the ferromagnetic layer, while the sin2 theta contribution, which prevails at room temperature and then decreases, is mainly associated with the spin Hall magnetoresistance originating from the Pt layer. The analysis of the corresponding angular dependences of the Hall voltage revealed non-trivial periodic oscillations in the second harmonic. Their appearance is found to be consistent with the manifestation of higher-order angle-dependent contributions to the field-like spin-orbit torque. The revealed strong influence of the electric current on the magnetization of the film studied, which ensures the higher-order effects manifestation, is of high relevance for magnetic memory design technologies.