Materials Science Research Lecture

Wednesday, October 12, 2022
4:00pm to 5:00pm
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Noyes 147 (J. Holmes Sturdivant Lecture Hall)
Neutron Scattering Studies of Exotic Magnetic Ground States
Bruce Gaulin, Professor, Physics and Astronomy, McMaster University,

NOTE: Every student or postdoc (any option!) will receive a $5 SmartCash "coffee credit" for each Materials Research lecture attended, in person or online. The credits will be tallied and issued after the last speaker of the term. *If you attend in person be sure to put your name on the sign-in sheet so you are counted.

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Webinar ID 850 1041 3991


Neutron scattering experiments have been key to understanding new magnetic materials, ever since the pioneering work of Cliff Shull and his contemporaries at Oak Ridge some 70 years ago. We now routinely use neutrons to understand magnetic structure, or lack thereof, as well as elementary magnetic excitations in new materials, on a range of energy scales. My research group's interests have tended to focus on new magnetic materials, mosty insulators, which have difficulty finding ordered ground states, due to geometrical frustration, quantum fluctuations or both.

I will illustrate this phenomena using a current research example of the geometrically-frustrated Ce-based pyrochlore, Ce2Zr2O7. In this material, the effective S=1/2 degree of freedom associated with the Ce3+ crystal field ground state doublet is known to act both as a conventional dipole magnetic moment, and as an octupole. This also constrains the form of its near-neighbour spin Hamiltonian, and allows for different ordered or quantum disordered ground states in this family of materials, where either the dipolar or octupolar nature of the S=1/2 degree of freedom dominates. I will describe our recent experiments [1,2], mostly neutron scattering and heat capacity, which show how the nature of the Ce3+ ground state doublet can be revealed, and how a particular form of exotic quantum spin liquid can be identified as the likely ground state in Ce2Zr2O7.

[1] J. Gaudet et al., Phys. Rev. Lett., 122, 187201 (2019).
[2] E.M. Smith et al. Phys. Rev. X, 12, 021015 (2022).

More about the Speaker:

Bruce D. Gaulin is Distinguished University Professor and Brockhouse Chair in the Physics of Materials at McMaster University. His undergraduate education was at McGill University, while his PhD was also at McMaster. He then went to Oak Ridge National Laboratory as a postdoc before returning to McMaster as faculty in 1988. With his graduate students and postdocs, he has carried out a large body of experimental studies, mainly using neutron scattering, aimed at understanding phase behavior and elementary excitations in (mostly) new magnetic materials. Gaulin is also prominent in professional neutron scattering and physics societies, having served as the President of the Neutron Scattering Society of America (NSSA) from 2008-2012, and the Canadian Association of Physicists in 2018-2019.

For more information, please contact Jennifer Blankenship by email at [email protected].