Optical observation of magnetization dynamics induced by spin-orbit torque in micro-magnetic ellipsoid

Abstract

This Thesis presents the results of current induced magnetization dynamics driven by spin-orbit torques (SOT) in the marco-sized ellipsoid device. Devices like magnetic tunnelling junctions and spin valves are used to investigate the mechanism of spin Hall effect and Rashba effect that the understanding of the underlying mechanism can lead to higher capacity, lower power consumption and higher processing speed spin-based devices. In this Thesis, we have investigated experimentally these phenomena with different configurations employing a variety of low-frequency SOT-induced ferromagnetic resonance, or quasi-static configurations in the Time-resolved scanning Kerr microscopy (TRSKM). In addition, an analytical approach and numerical calculations were used to gain insight into the underlying mechanisms. Devices that exploit spin currents for magnetisation reversal have recently received interest from the scientific community for their potential in non-volatile memories. Our experiments are focused on in-magnetized ellipsoids of Pt/CoFeB/MgO that present lower write currents and lower switching times. The dynamic response observed with optically detected ferromagnetic resonance configurations with TRSKM was compared with a macrospin model to understand the underlying SOT torques. Measurements with a bipolar electrical square-wave pulse to investigate the magnitude of DC SOT in micron-scale elements. The Quasi-static configuration with a magneto-optical method detects the out-of-plane magnetization directly linked with the current induced spin-orbit torque and DC Oersted field. The results presented in this Thesis from the experiments are expected to contribute to the efforts of determining the magnitude of DC induced SOT and further understanding of the underlying mechanisms in non-uniform magnetization dynamics.