Long-Range Antiferromagnetic Order in a Rocksalt High Entropy Oxide

Abstract

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 DC and AC magnetic susceptibility, elastic and inelastic neutron scattering measurements. The magnetic propagation wavevector is k=(½, ½, ½) based on the cubic structure Fm-3m, and the magnetic structure consists of ferromagnetic sheets in the (111) planes with spins antiparallel between two neighboring planes. Inelastic neutron scattering 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 extreme chemical disorder.

Magnetic properties of high entropy oxides

“…Besides, the possibilities of conducting double exchange interactions can also be anticipated in future via judicious choice of cation compositions in HEOs. 1,9,32,38,39 X-ray absorption and photoelectron spectroscopies indicate the presence of all the cations in their respective divalent oxidation state, among which Co 2+ (d 7 ), Cu 2+ (d 9 ) and Ni 2+ (d 8 ) are the magnetic ions. 3,8,38,39,63 The presence of the J-T active Cu 2+ brings about slight deviation from the ideal rocksalt structure locally, observed in terms of relative intensity mismatch between the (111) and (200) reflections in the XRD pattern.…”

“…Currently, there are eight major classes of HEOs that can be categorized based on the crystallographic structures: rocksalt, 1,3,8,9 fluorite, [10][11][12][13][14][15] bixbyite, 10,12,16 perovskite (cubic, orthorhombic, rhombohedral), 5,[17][18][19] spinel, 20,21 pyrochlore, 7,[22][23][24] layered (Ruddlesden-Popper and delafossite) [25][26][27] and magnetoplumbite. 28,29 Likewise, a broad range of properties, such as electrochemical, 2,[30][31][32] optical, 11,[33][34][35] magnetic, 21,29,34,[36][37][38][39][40][41][42]43 electronic and ionic transport, [44][45]…”

Holey Lamellar High‐Entropy Oxide as an Ultra‐High‐Activity Heterogeneous Catalyst for Solvent‐free Aerobic Oxidation of Benzyl Alcohol

“…Among the majority of complex metal oxides, high‐entropy oxides (HEO), defined as five or more near‐equimolar metal elements arranged deliberately in a single‐phase lattice with randomized distribution, have attracted ever‐increasing attention because of their diverse redox behavior, abundant cation compositions, and exceptional chemical and thermal stability . The multi‐electron redox properties in HEO make it a potential high‐performance catalyst for organic reactions.…”

Holey Lamellar High‐Entropy Oxide as an Ultra‐High‐Activity Heterogeneous Catalyst for Solvent‐free Aerobic Oxidation of Benzyl Alcohol

“…Among the majority of complex metal oxides,h ighentropy oxides (HEO), defined as five or more nearequimolar metal elements arranged deliberately in as inglephase lattice with randomized distribution, have attracted ever-increasing attention because of their diverse redox behavior, abundant cation compositions,a nd exceptional chemical and thermal stability. [17][18][19] Themulti-electron redox properties in HEO make it ap otential high-performance catalyst for organic reactions.T he most common approaches to synthesize HEO are arc-melting and spark plasma sintering methods under ultrahigh temperature. [20] However,limited by the current high temperature synthetic conditions,t he obtained micrometer-sized HEO grains expose only as mall portion of the effective catalytic sites,w hich greatly restricts their catalytic performance.F rom this point of view,t he synthesis of HEO catalyst with porous framework composed of self-linked HEO small nanoparticles will satisfy the requirement of catalytic reaction and provide opportunities for boosted catalytic activity.…”