Ferromagnetism above 1000 K in highly cation-ordered double-perovskite insulator Sr3OsO6

TL;DR

This study reports a new ferromagnetic insulator, Sr3OsO6, with a record Curie temperature exceeding 1000 K, driven by strong spin-orbit coupling and B-site ordering, promising for high-temperature spintronic devices.

Contribution

The paper demonstrates the synthesis and characterization of Sr3OsO6 with a record high Curie temperature, revealing the role of spin-orbit coupling and B-site ordering in its ferromagnetism.

Findings

Sr3OsO6 has a Curie temperature over 1000 K.

Atomic-resolution microscopy confirmed B-site ordering.

DFT calculations indicate spin-orbit coupling drives ferromagnetism.

Abstract

Magnetic insulators have been intensively studied for over 100 years, and they, in particular ferrites, are considered to be the cradle of magnetic exchange interactions in solids. Their wide range of applications include microwave devices and permanent magnets . They are also suitable for spintronic devices owing to their high resistivity, low magnetic damping, and spin-dependent tunneling probabilities. The Curie temperature is the crucial factor determining the temperature range in which any ferri/ferromagnetic system remains stable. However, the record Curie temperature has stood for over eight decades in insulators and oxides (943 K for spinel ferrite LiFe5O8). Here we show that a highly B-site ordered double-perovskite, Sr2(SrOs)O6 (Sr3OsO6), surpasses this long standing Curie temperature record by more than 100 K. We revealed this B-site ordering by atomic-resolution scanning transmission electron microscopy. The density functional theory (DFT) calculations suggest that the large spin-orbit coupling (SOC) of Os6+ 5d2 orbitals drives the system toward a Jeff = 3/2 ferromagnetic (FM) insulating state. Moreover, the Sr3OsO6 is the first epitaxially grown osmate, which means it is highly compatible with device fabrication processes and thus promising for spintronic applications.