Chiral Magnetization Switching Induced by Spin Orbit Torque in Pt/Co/Ta Structure

Abstract

Spin-orbit torque (SOT) has attracted extensive attention as an efficient method of controlling the magnetization of multilayered magnetic structures 1. To realize SOT-induced magnetization switching in the structure with perpendicular magnetic anisotropy (PMA), an external in-plane magnetic field is required to break the symmetry along the current direction2. The chiral magnetization switching behavior as a result of opposite applied field direction when the applied field is sufficiently large has been widely reported2–5. However, the SOT switching behavior under a small applied field is remained unclear. In this work, we investigated the SOT-induced magnetization switching behaviors in Pt/Co/Ta structure under the influence of external magnetic fields. The structure consisting of a thin Co layer sandwiched by Pt and Ta has an enhanced SOT, due to the opposite sign of spin Hall angle in Pt and Ta6. The characterized effective fields were found to be ~162 Oe per 1011 A/m2 for the damping-like term and ~108 Oe per 1011 A/m2 for the field-like term. SOT-induced magnetization switching was detected by measuring the Hall resistance using a sweeping DC current with a fixed longitudinal field $H_{x}$. The measurements were performed with up and down initial magnetized states under both positive and negative $H_{x}$, respectively. For each configuration, the measurement was repeated using different current sweeping directions, from −10 mA to +10 mA to −10 mA and from +10 mA to −10 mA to +10 mA. It is found that SOT-induced switching can be achieved under a field $H_{x} \ge 500$ Oe. The switching behaviors are influenced by all the directions of the field, the initial magnetization and the current sweeping when $H_{x} =500$ Oe. When $H_{x} >1$ kOe, the switching behavior is only dependent on the field direction. Figure 1 shows the experimental results under $H_{x} = \pm 500$ Oe. For $H_{x} = +500$ Oe, the down initial magnetization and current sweeping from +10 mA to −10 mA to +10 mA configuration result in different switching behavior. For $H_{x} = -500$ Oe, a different switching behavior happened in the configuration of up initial magnetization and current sweeping from +10 mA to −10 mA to +10 mA. When the applied $H_{x}$ increased to 1 kOe, the same switching behaviors were obtained for $H_{x} = +1$ kOe and $H_{x} = -1$ kOe, respectively. As shown in Fig. 2, the opposite switching loops were obtained due to the direction of the applied fields.