Octupolar vs Néel Order in Cubic 5d 2 double perovskites

• Published in: Physical review letters Vol. 124; no. 8
• Main Authors: Maharaj, D. D., Sala, G., Stone, M. B., Kermarrec, Edwin, Ritter, C., Fauth, F., Marjerrison, C. A., Greedan, J. E., Paramekanti, A., Gaulin, B. D.
• Format: Journal Article
• Language: English
• Published: American Physical Society 27-02-2020
• Subjects: Physics; 75.40.Gb; numbers: 75.25.j 75.40.Gb 75.70.Tj; numbers: 75.25.j; 75.70.Tj
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.124.087206

We report time-of-flight neutron spectroscopic and diffraction studies of the 5d 2 cubic double pervoskite magnets, Ba2M OsO6 (M = Zn, Mg, Ca). These cubic materials are all described by antiferromagnetically-coupled 5d 2 Os 6+ ions decorating a face-centred cubic (FCC) lattice. They all exhibit thermodynamic anomalies consistent with phase transitions at a temperature T * , and exhibit a gapped magnetic excitation spectrum with spectral weight concentrated at wavevectors typical of type I antiferromagnetic orders. While muon spin resonance experiments show clear evidence for time reversal symmetry breaking, no corresponding magnetic Bragg scattering is observed at low temperatures. These results are argued to be consistent with low temperature octupolar order, and are discussed in the context of other 5d DP magnets, and theories for d 2 ions on a FCC lattice which predict exotic orders driven by multipolar interactions.