Magnetization switching behavior for CoFeB/MgO and CoFeB/Ta multilayer films

Abstract

Recently, Ta/CoFeB/MgO/CoFeB/Ta magnetic tunneling junction (MTJ) films with perpendicular magnetic anisotropy (PMA) [1] are interesting because PMA can reduce the critical current for current-induced magnetization switching.It was reported that the PMA comes from the MTJ interface of the films [1].Therefore magnetization switching of the MTJ interface is a key characteristic of a spintronics device.Magnetic Compton profile (MCP) measurement can probe the magnetic quantum number m.In addition, MCP measurement can probe spin selective magnetization.Therefore It is possible to measure a spin selective magnetic hysteresis (SSMH) curve and orbital selective magnetization (orbital selective magnetic hysteresis (OSMH) curves) by combining an MCP measurement with a total magnetization measurement based on a vibrating sample magnetometer (VSM) or superconducting quantum interference device (SQUID) magnetometer [2].In this paper, we report magnetization switching behavior of the SSMH curves, OSMH curves and magnetic quantum number selective SSMH curves for the |m|=0, 1 and 2 magnetic quantum number states for CoFeB/MgO and CoFeB/Ta multilayer films from the view-point of the magnetization switching behavior with the PMA.MCP measurements were carried out on beamline BL08W at SPring-8, Japan.Elliptically polarized X-rays were monochromatized to be 182.6 keV and focused to a spot of 1×0.8 mm on the sample.The X-ray beams were parallel to the applied magnetic field.The applied magnetic fields were perpendicular to the film plane.The SSMH curves of the CoFeB/MgO and CoFeB/Ta multilayer films show magnetic shape anisotropy of an in-plane magnetic anisotropy.However, the OSMH curves of the CoFeB/MgO and CoFeB/Ta multilayer films show a step-function-like behavior with rather small magnetization switching fields as if they possess PMA.At the interface of the CoFeB/MgO multilayers, the OSMH curves are related to the SSMH curves trough the |m|= 2 magnetic quantum number states [3].On the contrary, at the interface of the CoFeB/Ta multilayers, the OSMH curves are related to the SSMH curves trough the |m|= 1 magnetic quantum number states.These facts indicate that the magnetization switching behavior is dominated by orbital magnetization.