Temperature dependence of spin–orbit torques in Pt/Co/Pt multilayers

Abstract

We studied the current-induced spin–orbit torques in a perpendicularly magnetized Pt (1 nm)/Co (0.8 nm)/Pt (5 nm) heterojunction by harmonic Hall voltage measurements. Owing to similar Pt/Co/Pt interfaces, the spin–orbit torques originated from the Rashba effect are reduced, but the contribution from the spin Hall effect is still retained because of asymmetrical Pt thicknesses. When the temperature increases from 50 to 300 K, two orthogonal components of the effective field, induced by spin–orbit torques, reveal opposite temperature dependencies: the field-like term (transverse effective field) decreases from 2.3 to 2.1 (10−6 Oe (A cm−2)−1), whereas the damping-like term (longitudinal effective field) increases from 3.7 to 4.8 (10−6 Oe (A cm−2)−1). It is noticed that the damping-like term, usually smaller than the field-like term in the similar Pt/Co interfaces, is twice as large as the field-like term. As a result, the damping-like spin–orbit torque reaches an efficiency of 0.15 at 300 K. Such a temperature-dependent damping-like term in a Pt/Co/Pt heterojunction can efficiently reduce the switching current density which is 2.30 × 106 A cm−2 at 300 K, providing an opportunity to further improve and understand spin–orbit torques induced by spin Hall effect.