Valence bond glass state in the 4$d^1$ fcc antiferromagnet Ba$_2$LuMoO$_6$

O. Mustonen; H. Mutch; H. C. Walker; P. J. Baker; F. C. Coomer; R. S. Perry; C. Pughe; G. B. G. Stenning; C. Liu; S. E. Dutton; E. J. Cussen

doi:10.1038/s41535-022-00480-4

arXiv · 2108.02209

Valence bond glass state in the 4$d^1$ fcc antiferromagnet Ba$_2$LuMoO$_6$

O. Mustonen·H. Mutch·H. C. Walker·P. J. Baker·F. C. Coomer·R. S. Perry·C. Pughe·G. B. G. Stenning·C. Liu·S. E. Dutton·E. J. Cussen

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Abstract

$B$-site ordered 4$d^1$ and 5$d^1$ double perovskites have a number of potential novel ground states including multipolar order, quantum spin liquids and valence bond glass states. These arise from the complex interactions of spin-orbital entangled $J_{eff}$ = 3/2 pseudospins on the geometrically frustrated fcc lattice. The 4$d^1$ Mo$^{5+}$ perovskite Ba$_2$YMoO$_6$ has been suggested to have a valence bond glass ground state. Here we report on the low temperature properties of powder samples of isostructural Ba$_2$LuMoO$_6$: the only other known cubic 4$d^1$ perovskite with one magnetic cation. Our muon spectroscopy experiments show that magnetism in this material remains dynamic down to 60 mK without any spin freezing or magnetic order. A singlet-triplet excitation with a gap of $\Delta$ = 28 meV is observed in inelastic neutron scattering. These results are interpreted as a disordered valence bond glass ground state similar to Ba$_2$YMoO$_6$. Our results highlight the differences of the 4$d^1$ double perovskites in comparison to cubic 5$d^1$ analogues, which have both magnetic and multipolar order.

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O. Mustonen, H. Mutch, H. C. Walker, P. J. Baker, F. C. Coomer, R. S. Perry, C. Pughe, G. B. G. Stenning, C. Liu, S. E. Dutton, E. J. Cussen. 2021-08-04. Valence bond glass state in the 4$d^1$ fcc antiferromagnet Ba$_2$LuMoO$_6$. https://doi.org/10.1038/s41535-022-00480-4

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