Abstract
A novel mixed‐valence osmate(V,VI) Sr 4 Os 3 O 12 is reported, which is attracted to a permanent magnet at room temperature (290 ± 5 K) but loses this property when heated or cooled. In this temperature interval, soft magnetic behavior but the saturation magnetization is only 0.05 μ B per formula unit. The compound crystallizes in the La 4 Ti 3 O 12 structure type. The structure is a rhombohedral stack of layered blocks, each of which can be considered as a section of three layers of the cubic perovskite structure cut perpendicular to one of its threefold axes. The Os–O–Os bond angle of about 175° favors superexchange that leads to antiferromagnetic coupling between the osmium atoms with 5 d 3 and 5 d 2 configurations. Sr 4 Os 3 O 12 exhibits strong lattice dynamics. One aspect is the antiferro‐rotative lattice modes of the corner‐sharing [OsO 6 ] octahedra, which freeze upon cooling. At 100 K, an ordered, yet twinned triclinic superstructure is formed. Strong spin‐orbit coupling and other effects cause deformations of the [OsO 6 ] octahedra that differ significantly at 300 K and 100 K, suggesting a change in the electronic configuration.
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