Absence of Long-Range Magnetic Ordering in a Trirutile High-Entropy Oxide (Mn$_{0.2}$Fe$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$)Ta$_{1.92}$O$_{6-\delta}$

Abstract

Functionalities of solid-state materials are usually considered to be dependent on their crystal structures. The limited structural types observed in the emerged high-entropy oxides put constraints on exploration of their physical properties and potential applications. Herein, we synthesized the first high-entropy oxide in a trirutile structure, (Mn$_{0.2}$Fe$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$)Ta$_{1.92}$O$_{6-\delta}$, and investigated its magnetism. The phase purity and high-entropy nature were confirmed by powder X-ray diffraction and energy-dispersive spectroscopy, respectively. X-ray photoelectron spectroscopy indicated divalent Mn, Co, Ni and Cu along with trivalent Fe. Magnetic properties measurements showed antiferromagnetic coupling and potential short-range magnetic ordering below ~ 4 K. The temperature-dependent heat capacity data measured under zero and high magnetic field confirmed the lack of long-range magnetic ordering and a possible low-temperature phonon excitation. The discovery of the first trirutile high-entropy oxide opens a new way for studying the relationship between the highly disordered atomic arrangement and their magnetic interaction. Furthermore, it provides a new direction for exploring functionalities of high-entropy oxides.