Absence of Long-Range Magnetic Ordering in a Trirutile High-Entropy Oxide (Mn0.2Fe0.2Co0.2Ni0.2Cu0.2)Ta1.92O6−δ

Functionalities of solid-state materials are usually considered to be dependent on their crystal structures. The limited structural types observed in the emerging high-entropy oxides put constraints on the exploration of their physical properties and potential applications. Herein, we synthesized the first high-entropy oxide in a trirutile structure, (Mn_0.2Fe_0.2Co_0.2Ni_0.2Cu_0.2)Ta_1.92O_6−δ, 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 property 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 fields 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 pathway for studying the relationship between the highly disordered atomic arrangement and magnetic interaction. Furthermore, it provides a new direction for exploring the functionalities of high-entropy oxides.

We report the first high-entropy oxide in a trirutile structure. Both powder XRD and EDS measurements confirm the high-entropy nature and the formula, (Mn_0.2Fe_0.2Co_0.2Ni_0.2Cu_0.2)Ta_1.92O_6−δ. Antiferromagnetic spin−spin coupling under high temperatures and short-range antiferromagnetic ordering under low temperatures were observed. The discovery of the first trirutile high-entropy oxide builds a new platform for investigating the interplay between high-entropy nature and its magnetism. Moreover, it allows the manipulation of a wider range of physical properties in high-entropy oxides.