Abstract: The field of high entropy oxides (HEOs) flips traditional materials science paradigms on their head by seeking to understand what properties arise in the presence of profound configurational disorder. This disorder, which emerges as the result of multiple elements sharing a single crystalline lattice appears to imbue some HEOs with functional properties that far surpass their conventional analogs. However, there are significant questions surrounding the actual degree of configurational disorder, its role in stabilizing the HEO phase, and its effect on other physical properties, including magnetism. Grasping the true extent of the elemental disorder in HEOs requires advanced characterization across orders of magnitude in length scales - from the atomic scale to the average structure, preferably with elemental sensitivity. In my talk, I will discuss my group's efforts toward addressing these questions using x-ray and neutron methods. We show that the magnetism of HEOs is highly tunable and properties such as ordering temperature, coercive field, and saturated moment, can be varied by orders of magnitude by subtle changes in composition. We further find that even at fixed composition, the magnetic properties of an HEO are highly dependent on the synthesis method due to differences in microstructure and chemical homogeneity. We conclude that chemical flexibility inherent to HEOs is complemented by strong synthesis method dependence, providing another axis along which to optimize these materials for a wide range of applications.
Bio: Alannah Hallas is an Associate Professor of Physics at the University of British Columbia, a Principal Investigator at the Blusson Quantum Matter Institute, and the Co-Director of CIFAR’s Quantum Materials Program. She completed her PhD in 2017 at McMaster University followed by a postdoctoral fellowship at Rice University. Alannah holds a Sloan Research Fellowship (2023-2025) and she was awarded the IUPAP Early Career Scientist Prize in the field of Magnetism in 2023. Alannah’s research focuses on the discovery and crystal growth of new quantum materials and their study using a range of neutron, x-ray, and muon techniques.
