Exchange coupling in synthetic anion-engineered chromia heterostructures

TL;DR

This paper demonstrates that nitrogen doping in chromium oxynitride thin films induces robust ferromagnetism and controllable exchange bias, offering new pathways for spintronic device applications.

Contribution

The study introduces synthetic anion engineering in chromium oxynitride to achieve ferromagnetism and exchange bias, expanding beyond traditional cation substitution methods.

Findings

Chromium oxynitride exhibits ferromagnetic and insulating states.

Nitrogen content influences crystal structure and magnetization.

Large, controllable exchange bias field achieved in heterostructures.

Abstract

Control of magnetic states by external factors has garnered a mainstream status in spintronic research for designing low power consumption and fast-response information storage and processing devices. Previously, magnetic-cation substitution is the conventional means to induce ferromagnetism in an intrinsic antiferromagnet. Theoretically, the anion-doping is proposed to be another effect means to change magnetic ground states. Here we demonstrate the synthesis of high-quality single-phase chromium oxynitride thin films using in-situ nitrogen doping. Unlike antiferromagnetic monoanionic chromium oxide and nitride phases, chromium oxynitride exhibits a robust ferromagnetic and insulating state, as demonstrated by the combination of multiple magnetization probes and theoretical calculations. With increasing the nitrogen content, the crystal structure of chromium oxynitride transits from trigonal (R3c) to tetragonal (4mm) phase and its saturation magnetization reduces significantly. Furthermore, we achieve a large and controllable exchange bias field in the chromia heterostructures by synthetic anion engineering. This work reflects the anion engineering in functional oxides towards the potential applications in giant magnetoresistance and tunnelling junctions of modern magnetic sensors and read heads.