Influence of rare earth metal Ho on the interfacial Dzyaloshinskii–Moriya interaction and spin torque efficiency in Pt/Co/Ho multilayers

Abstract

Owing to the large spin–orbit coupling and tunable magnetization, heavy rare-earth metals Gd and Tb have great effects on the enhancement of spin–orbit torque (SOT) and fast domain wall (DW) motion. However, the reports on the heavy rare-earth metal Ho with more 4f electrons in the research of spintronics are limited. In this work, we found that the interfacial Dzyaloshinskii–Moriya interaction (DMI) and SOT in Pt/Co/Ho multilayers can be strongly influenced by changing the thickness of the Ho (t_Ho) layer. At t_Ho = 2.4 nm, DMI exchange constant |D| and spin torque efficiency ξ_DL reach maximum values of 1.24 mJ m⁻² and 0.137 respectively, which are comparable with those in other Pt/Co/nonmagnetic (NM) layer structures. Deterministic current-induced magnetization switching with a low critical current density of 10⁶ A cm⁻² can be realized when t_Ho is less than 5 nm. The Néel-type DW with left-handed chirality and positive sign D can be determined by observing the current-induced asymmetric DW motion. Our results are helpful to prompt the application of heavy rare-earth elements in the fields of the DMI, SOT and chiral DW dynamics.