Lattice Instability and Competing Spin Structures in the Double Perovskite Insulator Sr2FeOsO6

TL;DR

This study investigates how lattice instability influences spin structure transitions in Sr2FeOsO6, revealing the interplay of lattice, spin, and electronic degrees of freedom in this double perovskite insulator.

Contribution

It demonstrates that lattice instability causes spin structure changes in Sr2FeOsO6, combining experimental and theoretical approaches to uncover the underlying mechanisms.

Findings

Lattice instability induces alternating Fe-Os distances.

Two distinct spin structures are observed at different temperatures.

Density-functional theory supports the experimental results.

Abstract

The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of spin structures that differ in the spin sequence of ferrimagnetic iron - osmium layers along the tetragonal c-axis. Neutron powder diffraction experiments, 57Fe M\"ossbauer spectra, and density-functional theory calculations suggest that this behavior arises because a lattice instability resulting in alternating iron-osmium distances fine-tunes the balance of competing exchange interactions. Thus, Sr2FeOsO6 is an example for a double perovskite, in which the electronic phases are controlled by the interplay of spin, orbital, and lattice degrees of freedom.