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

Rukma Nevgi; Subha Dey; Nandana Bhattacharya; Soheil Ershadrad; Tinku Dan; Sujay Chakravarty; S. D. Kaushik; Christoph Klewe; George E. Sterbinsky; Biplab Sanyal; Srimanta Middey

paper

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

arXiv:2406.01156

Abstract

Understanding how local distortions determine the functional properties of high entropy materials, containing five or more elements at a crystallographic site, is an open challenge. We address this for a compositionally complex spinel oxide (Mn $_{0.2}$ Co $_{0.2}$ Ni $_{0.2}$ Cu $_{0.2}$ Zn $_{0.2}$ )Cr $_{2}$ O $_{4}$ ( $A^{5}$ Cr $_{2}$ O $_{4}$ ). By comparatively examining extended X-ray absorption fine structure on $A^{5}$ Cr $_{2}$ O $_{4}$ and its parent counterparts $A$ Cr $_{2}$ O $_{4}$ 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 CuCr $_{2}$ O $_{4}$ is found to be completely suppressed in $A^{5}$ Cr $_{2}$ O $_{4}$ . 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. Remarkably, despite the presence of multiple magnetic ions and variable bond lengths, the mean field magnetic interactions of $A^{5}$ Cr $_{2}$ O $_{4}$ exhibit a striking resemblance to those of NiCr $_{2}$ O $_{4}$ . This compelling observation 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 in compositionally complex quantum materials, enabling the targeted design with tailored properties.