Local cation order and ferrimagnetism in compositionally complex spinel ferrites

We present an exploration of a family of compositionally complex cubic spinel ferrites featuring combinations of Mg, Fe, Co, Ni, Cu, Mn, and Zn cations, systematically investigating the average and local atomic structures, chemical short-range order, magnetic spin configurations, and magnetic properties. All compositions result in ferrimagnetic average structures with extremely similar local bonding environments; however, the samples display varying degrees of cation inversion and, therefore, differing apparent bulk magnetization. Additionally, first-order reversal curve analysis of the magnetic reversal behavior indicates varying degrees of magnetic ordering and interactions, including potentially local frustration. Finally, reverse Monte Carlo modeling of the spin orientation demonstrates a relationship between the degree of cation inversion and the spin collinearity. Collectively, these observations correlate with differences in synthesis procedures. This work provides a framework for understanding magnetic behavior reported for high-entropy spinels, revealing many are likely compositionally complex oxides with differing degrees of chemical short-range order-not meeting the community established criteria for high or medium entropy compounds. Moreover, this work highlights the importance of reporting complete sample processing histories and investigating local to long-range atomic arrangements when evaluating potential entropic mixing effects and assumed property correlations in high entropy materials. (C) 2022 Author(s).

Automated summary

This study investigates a family of compositionally complex cubic spinel ferrites, exploring their average and local atomic structures, chemical short-range order, magnetic spin configurations, and magnetic properties. The results show that all compositions exhibit ferrimagnetic average structures with similar local bonding environments, but they display varying degrees of cation inversion and apparent bulk magnetization. The analysis of magnetic reversal behavior reveals different degrees of magnetic ordering and interactions, including potential local frustration. Additionally, the relationship between the degree of cation inversion and spin collinearity is demonstrated through reverse Monte Carlo modeling. These findings are correlated with differences in synthesis procedures.