Two-Dimensional Magnetic Correlations and Partial Long-Range Order in Geometrically Frustrated Sr$_2$YRuO$_6$

Geometrically frustrated magnets are fascinating materials displaying a rich variety of physical states. The simplest three-dimensional structure leading to frustrated magnetism and the first one to be investigated is the face-centered cubic (FCC) lattice with antiferromagnetic nearest-neighbor interactions. Sr$_2$YRuO$_6$ is a particular example of this, crystallizing in the ordered double perovskite structure with the Ru$^{5+}$ ions defining an FCC magnetic network. Neutron diffraction experiments were performed on this material, revealing planar magnetic correlations that condense into a partial long-range ordered state with coupled alternate antiferromagnetic (AFM) YRuO$_{4}$ square layers coexisting with the short-range correlations below $T_{N1}=32$ K. A second transition to a fully ordered AFM state below $T_{N2}=24$ K is observed. The reduced dimensionality of the spin correlations in an FCC lattice is arguably due to a cancellation of the magnetic coupling between consecutive AFM square layers. The interesting magnetic phenomena observed here in Sr$_2$YRuO$_6$ are entirely driven by its lattice geometry, and may also occur in other FCC antiferromagnets.