Designing Magnetism in High Entropy Oxides

Abstract

Disorder can have a dominating influence on correlated and quantum materials leading to novel behaviors which have no clean limit counterparts. In magnetic systems, spin and exchange disorder can provide access to quantum criticality, frustration, and spin dynamics, but broad tunability of these responses and a deeper understanding of strong limit disorder is lacking. In this work, we demonstrate that high entropy oxides present an unexplored route to designing quantum materials in which the presence of strong local compositional disorder hosted on a positionally ordered lattice can be used to generate highly tunable emergent magnetic behaviors-from macroscopically ordered states to frustration-driven dynamic spin interactions. Single crystal La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 films are used as a structurally uniform model system hosting a magnetic sublattice with massive microstate disorder in the form of site-to-site spin and exchange type inhomogeneity. A classical Heisenberg model is found to be sufficient to describe how compositionally disordered systems can paradoxically host long-range magnetic uniformity and demonstrates that balancing the populating elements based on their discrete quantum parameters can be used to give continuous control over ordering types and critical temperatures. Theory-guided experiments show that composite exchange values derived from the complex mix of microstate interactions can be used to design the required compositional parameters for a desired response. These predicted materials are synthesized and found to possess an incipient quantum critical point when magnetic ordering types are designed to be in direct competition; this leads to highly controllable exchange bias sensitivity in the monolithic single crystal films previously accessible only in intentionally designed bilayer heterojunctions.

High-entropy oxides in the mullite-type structure

“…The magnetic behavior might thus be designed in HEO mullite-type materials by rational combinatio ns of REs with varying magnetic moments, as recently demonstrated for spinel HEOs 37 . Using a classical Heisenberg model, Mazza et al showed that compositionally disordered perovskites paradoxically can possess magnetic uniformity and that magnetic HEOs might not only pave the way to continuous control over ordering and critical temperatures, but also to induce highly controllable exchange bias behavior previously only accessible by heterojunctions 38 . Mullite-type materials, furthermore, demonstrate promise in catalysis as Sm2Mn4O10 has proven to be a highly active and stable catalyst for the oxidation of NO through a newly discovered cooperative lattice oxygen redox mechanism involving multiple Mn sites 16 .…”

Weak ferromagnetism in Tb(Fe0.2Mn0.2Co0.2Cr0.2Ni0.

“…Similarly, the Cr spectra (see the Supplemental Material [23]) show a pure presence of octahedral Cr 3+ [32]. From this mixture of valencies, we can already conclude ferromagnetism to emerge from X-O-Y superexchange interactions involving Mn 4+ , for example Mn 4+ − O − Co 2+ , Mn 4+ − O − Ni 2+ , while most combinations involving Fe or Cr are expected to support antiferromagnetism [19].…”

“…The diversity of material designs based on entropy-driven phase stabilization enables the engineering of novel complex oxides with interesting properties, including enhanced wear-resistant coatings, thermoelectric properties, thermal insulation, catalysis, water splitting, and energy storage [17,18]. With respect to HEOPs, La(Fe 0.2 Mn 0.2 Co 0.2 Cr 0.2 Ni 0.2 )O 3 (L5BO) and its various stoichiometric variations have been * alan.farhan@gmx.net the main focus of recent research [12,15,19,20]. Based on initial findings, L5BO features predominantly G-type antiferromagnetic order interspersed with ferromagnetic clusters [12,15].…”

Influences of powder morphology on the densification and microstructure of a ZrO2‐based nanocrystalline glass–ceramic

“…26,27 In comparison, the as-synthesized particle powder presented strong absorption bands of OH groups located at 1630 and 3460 cm −1 ; meanwhile, the absorption band of methyl groups at ∼2900 cm −1 overlapped with the absorption bands of OH groups located at 1630 cm −1 (Figure 4B), indicating that the as-synthesized particle contained water and a large amount of methyl groups. The water molecules are products of condensation reaction during the sol-gel process, 22 and the water molecules are trapped within the particles, whereas the methyl groups are products of hydrolysis of precursors, including TEOS and Zr(OPr) 4 . After calcination at 800 • C, the absorption band of methyl groups almost disappeared, indicating that methyl groups were burned out, which is consistent with the DSC-TG result (Figure 2).…”

“…However, natural minerals typically contain a lot of impurities and they had random morphologies and sizes, which results in a low quality of sintered ceramics. Nowadays, synthesized powder is utilized as raw powder to sinter advanced ceramics that show high microstructure homogeneity and excellent properties, such as mechanical, 2 optical, 3 magnetic, 4 and biological 5 properties, 6 due to the facts that synthesized powder has high purity, tunable morphology (particle, fiber, rod, lamellar, etc. ), controllable size, and size distribution.…”