Cluster Spin Glass State in Ba$_3$Sb$_{1+x}$Co$_{2-x}$O$_{9-δ}$: Cation Disorder and Mixed-Valence Co Dimers

Anzar Ali; Guratinder Kaur; Lukas Keller; Masahiko Isobe

doi:10.1103/k7mm-g2zc

paper

Cluster Spin Glass State in Ba $_{3}$ Sb $_{1 + x}$ Co $_{2 - x}$ O $_{9 - δ}$ : Cation Disorder and Mixed-Valence Co Dimers

arXiv:2506.19716 · doi:10.1103/k7mm-g2zc

Abstract

We investigate the structural, magnetic, and thermodynamic properties of \BSCO\ ( $x$ = 0.04, $δ$ = 0.54), a hexagonal perovskite featuring face-sharing CoO $_{6}$ octahedra that forms Co dimers. DC and AC magnetization measurements reveal a frequency-dependent spin-freezing transition consistent with glassy dynamics. AC susceptibility fits best to the Vogel-Fulcher model, indicating collective freezing of interacting spin clusters. Isothermal magnetization follows the Langevin function, suggesting finite-sized magnetic clusters rather than isolated paramagnetic moments. Non-equilibrium dynamics, evidenced by thermoremanent magnetization and memory effects, further support a spin-glass-like state. Heat capacity shows no sharp anomalies, and neutron powder diffraction confirms the absence of magnetic Bragg peaks down to 1.5~K, ruling out long-range magnetic order. Rietveld refinement reveals significant Co/Sb intersite disorder ( $\sim$ ~30\pct) and oxygen non-stoichiometry, introducing exchange randomness and frustration that drive the spin-glass-like behavior. Electrical resistivity exhibits Arrhenius-type temperature dependence with an activation energy of 0.173~eV, consistent with semiconducting behavior. Temperature-dependent X-ray diffraction shows no structural phase transitions, confirming that the spin-glass-like state is not lattice-driven. Our results establish \BSCO\ as a cluster spin-glass candidate, where Co dimers, disorder, and geometric frustration prevent long-range order, leading to slow spin dynamics. These findings highlight the role of cation disorder and oxygen vacancies in stabilizing unconventional magnetic states in cobalt-based hexagonal perovskites.

Cluster Spin Glass State in Ba3​Sb1+x​Co2−x​O9−δ​: Cation Disorder and Mixed-Valence Co Dimers

Abstract

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Cluster Spin Glass State in Ba $_{3}$ Sb $_{1 + x}$ Co $_{2 - x}$ O $_{9 - δ}$ : Cation Disorder and Mixed-Valence Co Dimers