3 research outputs found
Magnetic Texture in Insulating Single Crystal High Entropy Oxide Spinel Films
Magnetic insulators are important materials for a range of next generation
memory and spintronic applications. Structural constraints in this class of
devices generally require a clean heterointerface that allows effective
magnetic coupling between the insulating layer and the conducting layer.
However, there are relatively few examples of magnetic insulators which can be
synthesized with surface qualities that would allow these smooth interfaces and
precisely tuned interfacial magnetic exchange coupling which might be
applicable at room temperature. In this work, we demonstrate an example of how
the configurational complexity in the magnetic insulator layer can be used to
realize these properties. The entropy-assisted synthesis is used to create
single crystal (Mg0.2Ni0.2Fe0.2Co0.2Cu0.2)Fe2O4 films on substrates spanning a
range of strain states. These films show smooth surfaces, high resistivity, and
strong magnetic responses at room temperature. Local and global magnetic
measurements further demonstrate how strain can be used to manipulate magnetic
texture and anisotropy. These findings provide insight into how precise
magnetic responses can be designed using compositionally complex materials that
may find application in next generation magnetic devices
High Entropy Oxide Relaxor Ferroelectrics
Relaxor ferrolectrics are important in technological applications due to a
strong electromechanical response, energy storage capacity, electrocaloric
effect, and pyroelectric energy conversion properties. Current efforts to
discover and design new materials in this class generally rely on
substitutional doping of known ferroelectrics, as slight changes to local
compositional order can significantly affect the Curie temperature,
morphotropic phase boundary, and electromechanical responses. In this work, we
demonstrate that moving to the strong limit of compositional complexity in an
ABO3 perovskite allows stabilization of novel relaxor responses that do not
rely on a single narrow phase transition region. Entropy-assisted synthesis
approaches are used to create single crystal Ba(Ti0.2Sn0.2Zr0.2Hf0.2Nb0.2)O3
[Ba(5B)O] films. The high levels of configurational disorder present in this
system is found to influence dielectric relaxation, phase transitions,
nano-polar domain formation, and Curie temperature. Temperature-dependent
dielectric, Raman spectroscopy and second-harmonic generation measurements
reveal multiple phase transitions, a high Curie temperature of 570 K, and the
relaxor ferroelectric nature of Ba(5B)O films. The first principles theory
calculations are used to predict possible combinations of cations to quantify
the relative feasibility of formation of highly disordered single-phase
perovskite systems. The ability to stabilize single-phase perovskites with such
a large number of different cations on the B-sites offers new possibilities for
designing high-performance materials for piezoelectric, pyroelectric and
tunable dielectric applications