CINS Scattering Spotlight: Graham Johnstone
Source: Mitchell DiPasquale
Image: Spinel structure high entropy oxide (CrMnFeCoNi)3O4.
Everyone is waiting for the next big technological leap. As devices grow in complexity, the limits of materials and hardware are pushed toward their energetic and physical limits. Materials researchers across the globe redesign and tweak hardware to extend capabilities, but before too long these roadblocks will be unavoidable.
A technological revolution demands revolutionary hardware, and a new class of materials called high entropy oxides (HEOs) may have the necessary exotic electromagnetic properties to reinvigorate the field.
HEOs are crystalline materials with ordered oxygen and a mixture of randomly positioned metal ions. These unique materials possess intrinsic chemical disorder, lending fascinating properties that hold potential to develop technologies from reversible batteries to multiferroic components to make devices more efficient.
Graham Johnstone, a graduate student with Dr. Alannah Hallas at the Stewart Blusson Quantum Matter Institute of the University of British Columbia, is studying HEOs to define relationships between magnetism and chemical disorder.
High Entropy Oxide materials provide us with a wellspring of elemental combinations through which we can explore the relationship between magnetism and intense chemical disorder.
Graham Johnstone, Stewart Blusson Quantum Matter Institute, University of British Columbia
Graham is using a spinel structure HEO with the composition (CrMnFeCoNi)3O4 to dig deeper into these complex magnetic behaviours. In bulk, this HEO material remarkably retains its ferrimagnetic properties above room temperature. Theory predicts intrinsically disordered crystals that are doped with non-magnetic metals to exhibit decreased magnetism; however, HEOs have proven to be a stark exception to the rule.
To further define the origins of this magnetic paradox, Graham will use neutron diffraction to probe the magnetic properties of the various crystallographic sites in the spinel structure HEO. Neutrons are uncharged and possess the property of spin, offering an essential tool to probe the arrangement of magnetic moments deep inside materials at the sublattice scale – a feat not accomplished by other techniques.
In addition to shedding light on the nature of HEO magnetism, neutrons will also help Graham distinguish the cause of thermal changes in magnetic susceptibility to further explain the complex and remarkable magnetic properties of HEOs.
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