In this work we examine the low-temperature magnetic properties of the two double-perovskite compounds ${\mathrm{Sr}}_2$${\mathrm{CuWO}}_6$ and ${\mathrm{Sr}}_2$${\mathrm{CuMoO}}_6$ using magnetic susceptibility, muon spin rotation and relaxation, and neutron powder diffraction measurements. Additionally, the most relevant spin exchange interaction constants are derived from ab initio electronic structure calculations, aided by x-ray absorption spectroscopy. The compounds exhibit quasi-two-dimensional magnetic properties, with broad maxima at $T_{\max }$ = 83 and 95 K for ${\mathrm{Sr}}_2$${\mathrm{CuWO}}_6$ and ${\mathrm{Sr}}_2$${\mathrm{CuMoO}}_6$, respectively. However, three-dimensional long-range order takes place below $T_{\mathrm{N}}$ = 24(1) and 28(2) K for ${\mathrm{Sr}}_2$${\mathrm{CuWO}}_6$ and ${\mathrm{Sr}}_2$${\mathrm{CuMoO}}_6$, respectively. Our results show that the low-dimensional magnetic correlations are mainly due to the significant next-nearest-neighbor interactions in the $ab$ plane of the double-perovskite structure, whereas three-dimensional long-range magnetic order is caused by weaker next-nearest-neighbor interactions along the $c$ axis. Next-nearest-neighbor interactions are also slightly frustrated by weaker nearest-neighbor interactions within the $ab$ plane. Based on these results we predict the low-temperature magnetic structure in these compounds to be type-II antiferromagnetic order of the double-perovskite lattice.

• Received 9 February 2014
• Revised 4 April 2014

DOI:https://doi.org/10.1103/PhysRevB.89.134419