High Entropy Approach to Engineer Strongly Correlated Functionalities in Manganites

Abstract

Technologically relevant strongly correlated phenomena such as colossal magnetoresistance (CMR) and metal‐insulator transitions (MIT) exhibited by perovskite manganites are driven and enhanced by the coexistence of multiple competing magneto‐electronic phases. Such magneto‐electronic inhomogeneity is governed by the intrinsic lattice‐charge‐spin‐orbital correlations, which, in turn, are conventionally tailored in manganites via chemical substitution, charge doping, or strain engineering. Alternately, the recently discovered high entropy oxides (HEOs), owing to the presence of multiple‐principal cations on a given sub‐lattice, exhibit indications of an inherent magneto‐electronic phase separation encapsulated in a single crystallographic phase. Here, the high entropy (HE) concept is combined with standard property control by hole doping in a series of single‐phase orthorhombic HE‐manganites (HE‐Mn), (Gd0.25La0.25Nd0.25Sm0.25)1‐xSrxMnO3 (x = 0–0.5). High‐resolution transmission microscopy reveals hitherto‐unknown lattice imperfections in HEOs: twins, stacking faults, and missing planes. Magnetometry and electrical measurements infer three distinct ground states—insulating antiferromagnetic, unpercolated metallic ferromagnetic, and long‐range metallic ferromagnetic—coexisting or/and competing as a result of hole doping and multi‐cation complexity. Consequently, CMR ≈1550% stemming from an MIT is observed in polycrystalline pellets, matching the best‐known values for bulk conventional manganites. Hence, this initial case study highlights the potential for a synergetic development of strongly correlated oxides offered by the high entropy design approach.

High‐entropy oxides: Harnessing crystalline disorder for emergent functionality

“…(La 1/4 Nd 1/4 Sm 1/4 Gd 1/4 ) 1− x Sr x MnO 3 , with varying amounts of Sr as a hole dopant demonstrate a complex magneto‐electronic phase diagram with unique temperature dependencies. (La 1/4 Nd 1/4 Sm 1/4 Gd 1/4 ) 7/10 Sr 3/10 MnO 3 exhibits colossal magnetoresistance of 1550% stemming from a metal–insulator transition at 123 K, matching the best‐known values for bulk conventional manganites 182 . The possibility of compositionally tuning such electron‐correlated behavior may facilitate a deeper understanding of correlated phenomena in disordered crystals.…”

“…(La 1/4 Nd 1/4 Sm 1/4 Gd 1/4 ) 7/10 Sr 3/10 MnO 3 exhibits colossal magnetoresistance of 1550% stemming from a metal-insulator transition at 123 K, matching the best-known values for bulk conventional manganites. 182 The possibility of compositionally tuning such electron-correlated behavior may facilitate a deeper understanding of correlated phenomena in disordered crystals.…”

Tuneable Short-Range Antiferromagnetic Correlation in Fe-Containing Entropy Stabilized Oxides

“…Indeed, analysis of both the μSR spectral signal and neutron diffraction patterns points to a strong internal magnetic field with short-range correlation. This short-range magnetic correlation may be due to the strong electron correlation, which has been reported in both HEO and traditional perovskites. ,− However, since the AC magnetic measurement and M­(H) curves exclude a magnetic (spin) frustration with FM-like behavior while all of the SQUID magnetometry measurements suggest an AFM behavior in the low-temperature state, the low-temperature short-range magnetic correlation may only display AFM behavior, which is the main difference between our samples and the reported examples, in which the disorder magnetization has both FM and AFM contributions.…”

High-entropy rare earth materials: synthesis, application and outlook

“…Also, three distinct ground states were observed in the HE-RE oxides including insulating antiferromagnetic, unpercolated metallic ferromagnetic, and long-range metallic ferromagnetic. 151 These states coexist or compete due to hole doping and the intricate composition of multiple cations. The complexity gives rise to a substantial magnetoresistance, which is attributed to the metal-insulator transition observed in polycrystalline pellets.…”

“…Sarkar and co-workers presented a novel strategy for customizing strongly correlated functionalities in oxide systems through the HE design approach. 151 Nine HE manganites, denoted as (Gd 0.25 La 0.25 Nd 0.25 Sm 0.25 ) 1− x Sr x MnO 3 , featuring varying levels of Sr 2+ (h + ) dopant, were successfully stabilized as phase-pure orthorhombic perovskites with a homogeneous distribution of cations across their respective sublattices. The HR-TEM images revealed previously unknown lattice imperfections in HEOs, such as twins, stacking faults, and missing planes.…”