Electrically Enhanced Exchange Bias via Solid State Magneto-Ionics

TL;DR

This paper demonstrates voltage-controlled exchange bias in Gd/NiCoO thin films through solid-state magneto-ionics, enabling electric tuning of magnetic properties for energy-efficient device applications.

Contribution

It introduces a novel solid-state magneto-ionic method to electrically tune exchange bias via interfacial redox reactions in Gd/NiCoO films, not achievable with individual layers alone.

Findings

Exchange bias can be enhanced by 35% after voltage conditioning.

Interfacial ferromagnetic NiCo layer is confirmed by microscopy and neutron reflectometry.

Voltage and field cooling induce reversible control of exchange bias.

Abstract

Electrically induced ionic motion offers a new way to realize voltage-controlled magnetism, opening the door to a new generation of logic, sensor, and data storage technologies. Here, we demonstrate an effective approach to magneto-ionically and electrically tune exchange bias in Gd/Ni$_{1-x}$Co$_{x}$O thin films (x=0.50, 0.67), where neither of the layers alone is ferromagnetic at room temperature. The Gd capping layer deposited onto antiferromagnetic Ni$_{1-x}$Co$_{x}$O initiates a solid-state redox reaction that reduces an interfacial region of the oxide to ferromagnetic NiCo. Exchange bias is established after field cooling, which can be enhanced by up to 35% after a voltage conditioning and subsequently reset with a second field cooling. These effects are caused by the presence of an interfacial ferromagnetic NiCo layer, which further alloys with the Gd layer upon field cooling and voltage application, as confirmed by electron microscopy and polarized neutron reflectometry studies. These results highlight the viability of the solid-state magneto-ionic approach to achieve electric control of exchange bias, with potentials for energy-efficient magneto-ionic devices.