Octupolar versus Néel Order in Cubic 5d2 Double Perovskites

D. D. Maharaj, G. Sala, M. B. Stone, E. Kermarrec, C. Ritter, F. Fauth, C. A. Marjerrison, J. E. Greedan, A. Paramekanti, B. D. Gaulin

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Abstract

We report time-of-flight neutron spectroscopy and neutron and x-ray diffraction studies of the 5d2 double perovskite magnets, Ba2MOsO6 (M=Zn,Mg,Ca). These materials host antiferromagnetically coupled 5d2 Os6+ 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∗, and a gapped magnetic excitation spectrum with spectral weight concentrated at wave vectors typical of type-I antiferromagnetic orders. However, while muon spin resonance experiments show clear evidence for time-reversal symmetry breaking below T∗, we observe no corresponding magnetic Bragg scattering signal. These results are shown to be consistent with ferro-octupolar symmetry breaking below T∗, and are discussed in the context of other 5d double perovskite magnets and theories of exotic orders driven by multipolar interactions.

Original languageEnglish
Article number087206
JournalPhysical Review Letters
Volume124
Issue number8
DOIs
StatePublished - Feb 27 2020

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