Ionic substitutions in the Cu3TeO6 structure type and magnetic properties of “medium entropy” Cu3/2Mn1/2Co1/2Fe1/2SbO6

Cubic antiferromagnet Cu₃TeO₆ demonstrates interesting magnetic properties. Aimed at modification of them, we tried multiple ionic substitutions in its structure. However, single-phase materials could only be prepared with large fraction of the Jahn-Teller ions (Cu²⁺ and Mn³⁺), although formally isostructural bixbyites R₂O₃ (R₄O₆) with R = Sc, In, Tl, Sm…Lu exist with no Jahn-Teller ions. Moreover, ions having highest octahedral crystal field stabilization energy (Ni²⁺ and Cr³⁺) were found least tolerable. This points to Cu₃TeO₆ as a separate structure type, distinct from classical bixbyites. We report crystal structure, magnetic and thermodynamic properties of a rare single-phase multicomponent preparation, Cu_3/2Mn_1/2Co_1/2Fe_1/2SbO₆. The dc magnetic studies show that the formation of the ground spin-cluster state at T = 18 K is preceded by a broad anomaly at ∼122 K. Both specific heat and ac susceptibility data rule out the long-range magnetic ordering, in contrast to closely related Cu₂MSbO₆ (M = Mn or Fe).