Magnetoresistance curves of spin valves using the (1 1 0) cobalt ferrite pinning layer

Abstract

Listen

Translate article

Magnetic and magnetoresistance (MR) properties of spin valves composed of Co/Cu/Co/(1 1 0) cobalt ferrite (CFO) were studied, which showed complicated MR properties. It was confirmed from the in-plane magnetization curves that the epitaxial (1 1 0) CFO films have easy axes along the ⟨1 1 0⟩ direction and hard axes along the ⟨0 0 1⟩ direction due to in-plane tensile stress. The spin valves showed quite different MR curves depending on the direction of the magnetic field applied in the plane of (1 1 0) CFO. Butterfly-shaped MR curves, which implied the difference in the coercive fields between the top and bottom Co layers, were observed when the field was applied along the ⟨0 0 1⟩ direction of CFO. On the other hand, when the field was applied along the ⟨1 1 0⟩, unusually shaped MR curves, which showed large MR ratio in spite of the hard direction of the Co layer, were observed. This MR behaviour might indicate the parallel and anti-parallel magnetization configuration between the top and bottom Co layers at zero fields. These magnetic and MR properties could be explained using the micromagnetic calculation of magnetization processes by assuming strong 90° coupling between the bottom Co and CFO layers, and CFO pinning layers having continuous spin rotation at the interface near the bottom Co layer with an exchange stiffness coupling as a spring magnet.