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

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 direction
²
. The chiral magnetization switching behavior as a result of opposite applied field direction when the applied field is sufficiently large has been widely reported
^2–5
. 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 Ta
⁶
. The characterized effective fields were found to be ~162 Oe per 10
¹¹
A/m
²
for the damping-like term and ~108 Oe per 10
¹¹
A/m
²
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.