Spinel structure high entropy oxide (CrMnFeCoNi)3O4

Neutrons Clarify Convoluted Magnetic Materials

CINS Scattering Spotlight: Graham Johnstone

Source: Mitchell DiPasquale
Contact: webmaster@cins.ca
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.

Graham Johnstone

Graham Johnstone, Stewart Blusson Quantum Matter Institute, University of British Columbia

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.

CINS Scattering Spotlight aims to raise awareness for the world-class neutron research being conducted by students across Canada. We encourage you share your research stories by contacting drew.marquardt@uwindsor.ca.

Atomic structure of a mineral perovskite

Neutrons Point to Next-Generation Computer Memory Materials

CINS Scattering Spotlight: Dr Dalini Maharaj, TRIUMF

Source: Mitchell DiPasquale 
Contact: webmaster@cins.ca
Image: Crystal structure of a mineral perovskite. (Wikimedia CC-BY-SA 3.0)

As our music and movie libraries grow and the number of apps we use multiplies, everyone wants faster devices with larger data storage. Former McMaster PhD student Dalini Maharaj studies novel magnetic materials that could very well usher in the next generation data storage technology, particularly in disk drive read-and-write heads. In principle, one could reduce the size of the data storage unit if the data density could be increased in these hard-disks. New kinds of quantum materials are needed to fulfil this promise.

“Of course, before these new technologies can be realized, much work needs to be performed to understand the properties of the candidate materials.” – Dr. Dalini Maharaj, TRIUMF Post-Doctoral Fellow

Dr. Maharaj’s PhD work involved the study of the quantum magnetic properties of crystalline materials via X-ray and neutron scattering methods. Working in Prof. Bruce D. Gaulin’s group at McMaster University, she synthesized novel materials which are theoretically predicted to exhibit exotic magnetic properties. This class of materials, referred to as the double perovskites, have phases that involve `frustrated` magnetic interactions, whereby the magnetic dipoles of the atoms cannot arrange themselves into a low energy configurations. Members of this family are widely studied as they are shown to exhibit a wide variety of unique properties including superconductivity, ferroelectricity and colossal magnetoresistance, the latter being a prime candidate for increasing the data density of hard drives. In particular, Dalini’s doctoral work involved the study of non-trivial arrangements of magnetic atoms in d-electron double perovskites which are driven by magnetic interactions that can only be theoretically analysed with advanced quantum mechanics.

Dr. Dalini Maharaj

Neutrons are an indispensable probe of the magnetic properties of materials as they are electrically neutral and they possess the property of spin. These properties enable neutrons to deeply penetrate matter and interact directly with the magnetic degrees of freedom in solid state materials. The energy spectra which are obtained from neutron scattering experiments provide important clues for identifying the magnetic ground state of the materials being investigated.

Most recently, Dalini’s neutron scattering studies on the cubic double perovskite materials led to discover the first instance of octupolar order in d-electron magnets. This discovery highlights the relevance of multipolar interactions in heavy d-electron magnets and consequently, the potential for the realization of novel materials for future applications.

Upon completing her PhD, Dalini remained in the field of neutron sciences and is currently completing a postdoctoral fellowship at TRIUMF, through the University of Windsor, studying potential targets and moderators for a future compact accelerator neutron source.

CINS Scattering Spotlight aims to raise awareness for the world-class neutron research being conducted by students across Canada. We encourage you to share your research stories by contacting tharroun@brocku.ca

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