Giant Enhancement of Exchange Coupling in Entropy-Stabilized Oxide Heterostructures

Abstract

Entropy-stabilized materials are stabilized by the configurational entropy of the constituents, rather than the enthalpy of formation of the compound. A unique benefit to entropy-stabilized materials is the increased solubility of elements, which opens a broad compositional space, with subsequent local chemical and structural disorder resulting from different atomic sizes and preferred coordinations of the constituents. Known entropy-stabilized oxides contain magnetically interesting constituents, however, the magnetic properties of the multi-component oxide have yet to be investigated. Here we examine the role of disorder and composition on the exchange anisotropy of permalloy/(Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O heterostructures. Anisotropic magnetic exchange and the presence of a critical blocking temperature indicates that the magnetic order of the entropy-stabilized oxides considered here is antiferromagnetic. Changing the composition of the oxide tunes the disorder, exchange field and magnetic anisotropy. Here, we exploit this tunability to enhance the strength of the exchange field by a factor of 10x at low temperatures, when compared to a permalloy/CoO heterostructure. Significant deviations from the rule of mixtures are observed in the structural and magnetic parameters, indicating that the crystal is dominated by configurational entropy. Our results reveal that the unique characteristics of entropy-stabilized materials can be utilized and tailored to engineer magnetic functional phenomena in oxide thin films.

High‐Entropy Oxides: Fundamental Aspects and Electrochemical Properties

“…More recently, there have been reports regarding the thermal properties of HEOs, where an interesting correlation between the low thermal conductivity and the disorder in the systems (i.e., multiple cations acting as phonon scatters) has been observed . Reports are also available on thin film deposition, sintering, mechanical, magnetic, and optical properties of HEOs. Theoretical studies have not been extensively performed on all classes of HEOs, nevertheless, there are reports on R‐HEO, which correlate: (i) the lattice distortion with the Jahn–Teller effect and (ii) the phase composition with the thermodynamic parameters .…”

Review of high entropy ceramics: design, synthesis, structure and properties

“…Epitaxial growth is also useful for preparing structures that are not possible to produce by solid state reaction and wet chemical methods, such as superlattices and heterostructures. 52…”

Solid‐state synthesis of multicomponent equiatomic rare‐earth oxides

“…Recently the high-entropy concept has been extended to metal diborides 17 carbides 18 nitrides, 19 and oxides. 20 The field of high-entropy oxides attracts attention as a current research topic, [21][22][23][24][25][26] particularly due to the functional properties that have been reported, such as high dielectric constant, 27 lithium superionic conductivity, 28 magnetic properties, [29][30][31] electrical and thermal conductivities, 32,33 reversible energy storage, 34 and high catalytic activity in CO oxidation. 35 Launching the field of high-entropy oxides, Rost 20 reported a single rocksalt structure for (Mg ,Ni, Co, Cu, Zn)O pellets produced using solid-state synthesis.…”