Long-Range Antiferromagnetic Order in a Rocksalt High Entropy Oxide

We report for the first time the magnetic structure of the high entropy oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O using neutron powder diffraction. This material exhibits a sluggish magnetic transition but possesses a long-range ordered antiferromagnetic ground state, as revealed by direct current and alternating current magnetic susceptibility, neutron diffraction, and spectroscopy. The magnetic propagation wavevector is k = (1/2, 1/2, 1/2) based on the cubic structure Fm 3̅m, and the magnetic structure consists of ferromagnetic sheets in the (111) planes with spins antiparallel between two neighboring planes. Neutron spectroscopy reveals strong magnetic excitations at 100 K that survive up to room temperature. This work demonstrates that entropy-stabilized oxides represent a unique platform to study long-range magnetic order with an extreme chemical disorder.