Research Projects

Transition-metal (TM) oxides are well known for their complex magneto-electronic phenomena—such as colossal magnetoresistance (CMR), metal-insulator transitions (MIT), multiferroicity, and spin-dependent transport—which are essential for developing spintronic technologies. These effects originate from the delicate interplay among lattice, charge, spin, and orbital degrees of freedom, primarily mediated by exchange coupling between TM cations through oxygen anions. Traditional methods for tuning these properties rely on charge doping or epitaxial strain. This project proposes an alternative route: engineering chemical disorder in rare-earth transition-metal perovskite high-entropy oxides (RE–TM P-HEOs) to access novel functionalities within a single-phase solid solution. High-entropy oxides (HEOs) are an emerging class of materials stabilized by high configurational entropy due to multiple cations (typically five or more) randomly occupying a given cation sublattice. In RE–TM P-HEOs, such disorder is introduced on the A- and/or B-sites of the perovskite lattice, offering a vast compositional landscape. The resulting variations in TM–O–TM bond geometries give rise to competing magnetic exchange pathways and, consequently, rich magneto-electronic phase behavior. Initial studies, including those from our group, have shown that P-HEOs can exhibit properties such as intrinsic exchange bias, broad magnetic transition ranges, and strain-tunable perpendicular magnetic anisotropy—all within a structurally single-phase system. These findings challenge the conventional view that such multifunctionality requires heterostructures or composite architectures. This project will investigate the magneto-electronic behavior of RE–TM P-HEOs using a hybrid experimental–computational approach. The central objective is to systematically tune properties such as exchange bias, MIT, and PMA through two parallel strategies: first, via compositional tuning through aliovalent doping and deviations from equiatomic proportions, thereby modifying local bonding environments and cation valence states; and second, by applying epitaxial strain in single-crystal thin films to geometrically modulate the TM–O–TM bond network. Preliminary results suggest that P-HEOs can accommodate large strain through unconventional relaxation mechanisms, providing further control over their functional response. Despite this promise, key gaps remain in current understanding. These include the absence of a predictive framework for identifying phase-pure compositions, limited knowledge of local structural features such as short-range ordering and lattice distortions, poor understanding of interfacial effects in epitaxial films, and the lack of mechanistic insight into observed behaviors such as intrinsic exchange bias and MIT. This proposal aims to directly address these challenges by employing a combined experimental–computational research approach. Through this work, we aim to develop a predictive model linking chemical disorder and epitaxial strain with magneto-electronic response; experimentally validate descriptors for phase stability in non-equiatomic systems; and establish clear relationships between observed functionalities and local structural features such as magnetic domains, short-range disorder, and bonding geometries. These insights will not only aid in the discovery of new HEOs with magneto-electronic functionalities but also contribute to the broader understanding of correlated electron systems under extreme chemical disorder. Importantly, while the proposal is grounded in fundamental research, its outcomes could support broader national initiatives such as the National Quantum Mission, particularly in advancing material platforms for spin-based logic and memory, where control over spin currents and spin–orbit coupling is essential.