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 the switching behavior 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 achived a magnetic field free current-induced deterministic switching in the films with small tilt in anisotropy axis. We realized this in devices where the ultrathin Co layer was grown using an oblique angle sputter deposition technique that had resulted in a small tilt of magnetic anisotropy from the film normal. By performing out-of-plane magnetization hysteresis measurements under bias magnetic field applied along various in-plane directions the tilt angle was estimated to be around 3.3 (±0.3) degrees. A deterministic current-induced magnetization switching could be achieved when the in-plane current was applied perpendicular to the anisotropy tilt axis, but the switching was stochastic when the current was applied in the direction of the tilt (in the tilt plane). By preparing Pt/Co/Pt stacks with unequal top and bottom Pt thickness, sufficient spin-orbit torque (SOT) could be applied to switch the magnetization of the Co layer at current densities as low as 1.5×107 A/cm2. The efficiency of current induced magnetization reversal in Pt (4 nm)/Co (0.45 nm)/ Pt (1 nm)
devices was calculated to be 40 Oe=1e7 A/cm2.