Magnetic storage devices are having the advantage of its non-volatile nature. But now it is failing to keep up with the requirements of ever growing modern semiconductor technology. The problem is that the requirement of moving parts in the device which limits the speed of a disc. We want to keep increasing the density of data and at the same time improve the speed. This is a tremendous task to carry out. There are multiple ways in which we can switch the magnetization of a sample. For the industry, it is about how fast and cheap it can be. Here we have investigated spin orbital torque (SOT) induced switching of ultra-thin magnetic stack in the presence of a vector magnetic field and current. We have used a sample with anisotropy axis perpendicular to its plane.
Our samples were ultra-thin layers of Pt/Co/Pt, deposited using magnetron sputtering situated inside the clean room facility at IISc. These films were characterized using Kerr microscopy, SQUID magnetometer, X-ray Photoelectron spectroscopy (XPS), Scanning Electron Microscope (SEM), Atomic force microscope (AFM) and X-ray diffractometer (XRD). The current induced magnetization reversal studies were carried out using Kerr microscopy, which was the most significant part of our project.
SOT-induced magnetization reversal is usually achieved with the aid of an in-plane bias magnetic field. In our study we achieved a SOT-induced magnetization reversal without an in-plane magnetic field in films whose magnetic anisotropy axis is tilted by a small angle with the perpendicular to the plane of the sample. Tilt in the anisotropy axis was achieved through an oblique angle deposition of the Co layer. This tilt was measured by carrying out, out-of-plane magnetization hysteresis measurements, under in-plane bias magnetic field. Through the measurement we obtained a tilt angle of 3.3 (±0.3) degrees. In case of the control sample which has no tilted anisotropy we observed deterministic current-induced magnetization switching when the in-plane current was applied perpendicular to the anisotropy tilt axis, but when the current was along the tilt direction the switching was stochastic. By optimizing the layer thickness we managed to achieve 40 Oe/1e7 A/cm2 current induced magnetization reversal efficiency and we could bring down the critical current density for SOT switching to be as 1.5×1e7 A/cm2.