Room-temperature ferromagnetic insulating state in highly cation-ordered epitaxial oxide double perovskite

TL;DR

This paper reports the synthesis of room-temperature ferromagnetic insulator films in a double perovskite by controlling cation order, revealing a new state with high Curie temperature and potential for oxide quantum materials.

Contribution

It demonstrates a novel method to achieve ferromagnetic insulating states in epitaxial oxides through cation ratio control, distinct from known metallic phases.

Findings

Achieved room-temperature ferromagnetic insulator films with high Curie temperature (~400 K).

Identified the role of Fe3+-Fe3+ and Fe3+-Re6+ bonding in stabilizing the FMI state.

Opened pathways for oxide quantum materials and heterostructure development.

Abstract

Ferromagnetic insulators (FMIs) are one of the most important components in developing dissipationless electronic and spintronic devices. However, since ferromagnetism generally accompanies metallicity, FMIs are innately rare to find in nature. Here, novel room-temperature FMI films are epitaxially synthesized by deliberate control of the ratio of two B-site cations in the double perovskite Sr2FeReO6. In contrast to the known ferromagnetic metallic phase in stoichiometric Sr2FeReO6, a FMI state with a high Curie temperature (Tc~400 K) and a large saturation magnetization (MS~1.8 {\mu}B/f.u.) is found in highly cation-ordered Fe-rich phases. The stabilization of the FMI state is attributed to the formation of extra Fe3+-Fe3+ and Fe3+-Re6+ bonding states, which originate from the excess Fe. The emerging FMI state by controlling cations in the epitaxial oxide perovskites opens the door to developing novel oxide quantum materials & heterostructures.