Local structural distortions drive magnetic molecular field in compositionally complex spinel oxide

Understanding how local distortions determine the functional properties of high entropy materials, containing five or more elements at the same crystallographic site, is an open challenge. We address this for a compositionally complex spinel oxide (Mn_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)Cr₂O₄ (A⁵Cr₂O₄). By comparatively examining extended X-ray absorption fine structure on A⁵Cr₂O₄ and its parent counterparts, ACr₂O_4, along with density functional theory calculations for multiple configurations, we find that the element-specific distortions go beyond the first neighbor. Specifically, the strong Jahn-Teller distortion present in CuCr₂O₄ is found to be completely suppressed in A⁵Cr₂O₄ even locally. Instead, there is a broad distribution of Cu-O and Cu-Cr bond distances, while other A-O distances acquire certain specific values. This study demonstrates the additional flexibility of a cationic sublattice in maintaining a uniform long-range structure, in contrast to previous reports showing only the accommodative anionic sublattice. The mean-field magnetic interactions of A⁵Cr₂O₄ exhibit a striking resemblance to those of NiCr₂O₄, despite the presence of multiple magnetic ions and variable bond lengths. This originates from the comparability of bond lengths around Cr in both materials. Our study paves the way for a deeper understanding of the impact of local structural distortions on the physical properties of compositionally complex quantum materials.