Magnetic phase transitions in Ta/CoFeB/MgO multilayers

TL;DR

This study investigates magnetic phase transitions at the interface of Ta/CoFeB/MgO multilayers, revealing an ultrathin magnetic oxide layer that undergoes a temperature-driven phase change impacting spintronic device performance.

Contribution

It identifies and characterizes a magnetic oxide layer at the interface, providing new insights into interfacial effects in CoFeB-based multilayers.

Findings

An ultrathin magnetic oxide forms at the CoFeB/MgO interface.

The oxide transitions from antiferromagnetic insulator to weak ferromagnet around 160 K.

This phase transition influences the magnetic properties relevant for spin torque memories.

Abstract

We study thin films and magnetic tunnel junction nanopillars based on Ta/Co$_{20}$Fe$_{60}$B$_{20}$/MgO multilayers by electrical transport and magnetometry measurements. These measurements suggest that an ultrathin magnetic oxide layer forms at the Co$_{20}$Fe$_{60}$B$_{20}$/MgO interface. At approximately 160 K, the oxide undergoes a phase transition from an insulating antiferromagnet at low temperatures to a conductive weak ferromagnet at high temperatures. This interfacial magnetic oxide is expected to have significant impact on the magnetic properties of CoFeB-based multilayers used in spin torque memories.