Suppression of orbital ordering and emergence of a glassy magnetic state in a high-entropy spinel vanadate
High-entropy oxides provide a unique platform for exploring the interplay between configurational disorder and correlated electronic states. We report on structural, thermodynamic, and magnetic properties of the high-entropy spinel vanadate (Li$_{0.2}$Mg$_{0.2}$Mn$_{0.2}$Co$_{0.2}$Zn$_{0.2}$)V$_2$O$_4$, in which orbital-active V ions occupy the pyrochlore sublattice. X-ray diffraction measurements reveal that the cubic spinel structure is preserved at temperatures down to 5 K without any detectable symmetry lowering. Unlike conventional spinel vanadates exhibiting a symmetry-lowering structural transition driven by orbital ordering, the compound that we study exhibits a suppression of long-range orbital ordering in the high-entropy state. Magnetic susceptibility measurements show glassy magnetic freezing at temperatures below $\sim$20 K, while specific-heat measurements reveal no anomaly associated with long-range ordering down to 3 K. Frequency-dependent ac susceptibility reveals pronounced glassy dynamics. Analyses based on the Mydosh parameter, dynamic scaling law, and Vogel--Fulcher law suggest an intermediate dynamical regime between canonical spin-glass and cluster-glass behavior. Furthermore, Cole--Cole analyses reveal systematic deviations from a single Debye relaxation process, indicating the presence of heterogeneous magnetic relaxation dynamics near the freezing regime. Our results demonstrate that, in a frustrated spinel vanadate, high configurational entropy suppresses long-range orbital ordering and stabilizes a heterogeneous glassy magnetic state, highlighting the combined roles of geometrical frustration, orbital degrees of freedom, and configurational disorder in high-entropy magnets.