Multicomponent equiatomic high entropy oxides - synthesis and magneto-electronics properties

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Multicomponent high entropy oxides (HEOs) represent a group of single phase oxide solid solutions consisting of five or more cations in nearly equiatomic proportion. Although the field of HEO is barely five years old, several intriguing structural and functional features of different classes of HEOs have been already reported, which include some of our own pioneering investigations performed within the framework of the initial funding period. More specific achievements of the initial funding period are as follows: (a) discovery of rare-earth transition metal based perovskite-HEOs (P-HEOs) and anionic disordered high entropy oxyfluorides (HEOFs), (b) demonstration of the superior electrochemical performance of rocksalt-HEOs and HEOFs as anodes and cathodes for Li-ion batteries (d) elucidation of the reversibly controlled band structure of fluorite-HEOs and finally, (e) the observation of exotic magnetic phenomena stemming from the extreme chemical disorder in P-HEOs, such as exchange bias, large magneto-crystalline anisotropy, large coercive fields at room temperature, etc. These results are the outcome of rather fundamental but diverse investigations, intended to scout whether the field of HEOs is worth studying. In effect, this pioneering research has already highlighted the plethora of unprecedented physico-chemical phenomena that the multicomponent high entropy based design approach can offer. The main thrust of this research proposal will be the introduction of a new class of materials to the field of magneto-electronics with either enhanced or hitherto unknown functionalities by using chemical disorder on both cationic and anionic sites offered by the high entropy based approach. The group of rare-earth transition metal P-HEOs is chosen as the primary HEO-class for this exploration based on the already obtained results, which indicate their strong inherent connection between the chemical disorder, prominent structural distortions and stabilization of unusual spin-electronic states. Naturally, P-HEOs as a material class is also an optimal choice due to the overwhelming richness of the physical properties of the parent perovskites, e.g., colossal magnetoresistance, magneto-electronic phase separation, Mott transitions, spin-electron correlations, magneto-electric effect, etc. The modi operandi for tuning the exchange interactions among the constituent transition metal cations and thereby the magneto-electronic features will include electron or hole doping by altering the cationic sub-lattice(s), external strain introduction by epitaxial thin film deposition and reversible insertion and extraction of anions (O2- or F-) via heat treatments or electrochemistry. Our group’s long term experience on thin film deposition, magnetism, magneto-electronics/-ionics and electrochemical control of magnetism in combination with the newly gained expertise on HEOs will be utilized to achieve the envisaged goal of “novel magneto-electronics with HEOs”.