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Dynamical magnetism in the disordered cubic lattice material γ−Ba3CoNb2O9

Fanjun Xu1,2,*, Ralf Feyerherm1, Cecilie Glittum1,3,4,†, Thomas J. Hicken5, Hubertus Luetkens5, Jonas A. Krieger5, Cintli Aguilar-Maldonado1, Sven Luther6, Lucy K. Saunders7 et al.

Sarah Day7, Clemens Ritter8, Peter Fouquet8, Margarita Russina1, Karel Prokeš1, A. T. M. Nazmul Islam1, and Bella Lake1,2,‡

  • *Contact author: fjxuphys@gmail.com
  • †Contact author: cecilgl@uio.no
  • ‡Contact author: bella.lake@helmholtz-berlin.de
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Phys. Rev. B 114, 194423 – Published 23 October, 2026

DOI: https://doi.org/10.1103/jsvt-jc4l

Abstract

γ−Ba3CoNb2O9 realizes a disordered simple-cubic spin-1/2 lattice in which Co2+ ions randomly occupy one-third of the sites, placing the system just above the site-percolation threshold for magnetic order. Specific-heat, susceptibility, neutron spin-echo, and muon spin-rotation measurements reveal a broad thermodynamic crossover, short-range magnetic correlations, and persistent fast spin dynamics down to at least 0.1 K, with no evidence for static order or conventional spin-glass freezing within the experimental time windows. Monte Carlo simulations yield a broad distribution of orphan spins, finite clusters, and an infinite network. The weakly correlated spin fraction (≈8.2%) inferred phenomenologically from magnetization is consistent with the calculated orphan-spin fraction (≈8.8%). Exact diagonalization of a diluted S=1/2 Heisenberg model captures the broad magnetic specific-heat anomaly and supports the coexistence of weakly and strongly correlated spin environments. These results support a picture in which spin-1/2 quantum fluctuations, together with dilution and proximity to the percolation threshold, can support a disorder-driven dynamical state with short-range correlations in three dimensions, distinct from both classical spin glasses and geometrically frustrated quantum spin liquids.

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Outline

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Phys. Rev. B 114, 194423– Published 23 October, 2026
  • Received 2 April 2026
  • Revised 10 August 2026
  • Accepted 22 September 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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