Professor Alannah Hallas

Department of Physics and Astronomy

Stewart Blusson Quantum Matter Institute

University of British Columbia

Host:  Gannon

Title: Intertwined Dipolar and Quadrupolar Correlations in the Pyrochlore Tb2Ge2O7

Abstract:  Rare earth pyrochlores are model systems for the study of highly frustrated magnetism, in large part, because the majority of these materials have a clean separation of energy scales between their single-ion properties and their collective interactions. Terbium pyrochlores represent the exception, where a low energy crystal field excitation profoundly affects the spin interactions and imbues these materials with especially complex phase behavior. We find that the magnetic states of the terbium pyrochlores evolve over three distinct temperature regimes, strongly suggesting a universality to their low temperature phase behavior. In this talk, I will present a comprehensive heat capacity and neutron scattering study of Tb2Ge2O7 where, for the first time, we have been able to elucidate the nature of each of these three regimes. We find that the complex phase behavior of the terbium pyrochlores originates from not only the usual geometric frustration but also frustration due to the competition between magnetic dipoles and electric quadrupoles.