The semiconductor ${\mathrm{Sr}}_2{\mathrm{FeOsO}}_6$, 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, ${}^{57}\mathrm{Fe}$ Mössbauer 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, ${\mathrm{Sr}}_2{\mathrm{FeOsO}}_6$ is an example of a double perovskite, in which the electronic phases are controlled by the interplay of spin, orbital, and lattice degrees of freedom.

• Received 21 June 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.167205