Octupolar versus Néel Order in Cubic 5d2 Double Perovskites

We report time-of-flight neutron spectroscopy and neutron and x-ray diffraction studies of the 5d^{2} double perovskite magnets, Ba_{2}MOsO_{6} (M=Zn,Mg,Ca). These materials host antiferromagnetically coupled 5d^{2} Os^{6+} ions decorating a face-centered cubic (fcc) lattice and are found to remain cubic down to the lowest temperatures. They all exhibit thermodynamic anomalies consistent with a single phase transition at a temperature T^{*}, …