Designing Magnetism in High Entropy Oxides

Perfection is often the goal in the synthesis of new materials, striving to be free from disorder and defects. However, these imperfections are often the driver of some of the most important materials breakthroughs in modern physics – from high temperature superconductivity to the quantum anomalous Hall effect. In this spirit we explore configurational disorder in magnetic materials, enabled by the “high entropy” approach – where a combination of magnetically active cations can create local spin and exchange interaction disorder.

This has been realized in single crystal epitaxial films of the ABO₃ perovskite La(Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)O₃, where considering only the first nearest neighbors 15 atomic pairs with different exchange interactions and 5 possible spin states are uniformly distributed on a cubic lattice [1]. XRD and STEM-EELS studies confirm crystallinity, epitaxy, and full site mixing of the 5 B-site elements (no single element clustering) [2]. Experimental results from neutron studies, XMCD, and SQUID magnetometry demonstrate unexpected long-range magnetic ordering arising from the highly frustrated local environment. Furthermore, we demonstrate an understanding of only the first nearest neighbor interactions allows for reliable prediction of prevailing magnetic phase and phase degeneracy both through hole doping and manipulation of choice of magnetic cations [3,4]. These results are discussed in the broader context of emerging materials – where high entropy oxides exhibit an exciting avenue in the exploration of new strongly correlated and quantum materials.