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MA: Fachverband Magnetismus
MA 17: PhD Symposium: Quantum Magnets: Frustration and Topology in Experiment and Theory (jointly with Young DPG (jDPG)
MA 17.2: Hauptvortrag
Dienstag, 21. März 2017, 10:30–11:15, HSZ 04
Ground State Selection in Quantum Pyrochlore Magnets — •Bruce D. Gaulin — McMaster University, Hamilton, Ontario, Canada
Rare-earth (RE) based cubic pyrochlore magnets, with composition RE2B2O7, are characterized by having RE3+ ions decorate a network of corner-sharing tetrahedra, one of the canonical architectures supporting geometric frustration in three dimensions. For a given RE2B2O7 series, such as with the non-magnetic B=Ti4+, crystalline electric field effects give different anisotropies for the magnetic RE ion, while varying crystal chemistry results in different magnetic interactions. The combination of these two produces a remarkable diversity of exotic magnetic ground states across a series such as RE2Ti2O7. I will describe this series of materials, and point out how local XY anisotropy gives rise to Seffective=1/2 quantum spins for Yb2Ti2O7 and Er2Ti2O7. These two quantum pyrochlore magnets display very different ground states, a highly disordered, candidate quantum spin ice state in Yb2Ti2O7, and a non-linear Neel state selected by the "order-by-disorder" mechanism for Er2Ti2O7, due to their net ferromagnetic and antiferromagnetic interactions, respectively. I will focus mainly on experimental techniques, principally neutron scattering and heat capacity measurements, that can provide microscopic information on both the ground state and the excitations within the exotic ground states which these materials display.