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Title: | The Effect of Chemical Pressure on the Magnetic Ground States of Rare Earth Pyrochlores |
Other Titles: | Application of Chemical Pressure to Rare Earth Pyrochlores |
Authors: | Hallas, Alannah M. |
Advisor: | Luke, Graeme M. |
Department: | Physics and Astronomy |
Keywords: | Magnetism;Pyrochlore;Frustration;Chemical Pressure;Neutron Scattering;Muon Spin Relaxation;High Pressure Synthesis |
Publication Date: | Nov-2017 |
Abstract: | The rare earth pyrochlore oxides, with formula R2B2O7, are a chemically versatile family of materials that exhibit a diverse array of magnetic phenomena. In this structure the R and B site cations each form a corner-sharing tetrahedral network, a motif that is prone to intense geometric magnetic frustration. As a consequence of their magnetic frustration, rare earth pyrochlores are observed to host a number of remarkable states such as spin ice and spin liquid states. In this thesis we endeavor to explore the phase diagrams of the rare earth pyrochlores through the lens of chemical pressure. Chemical pressure is applied by varying the ionic radius of the non-magnetic B site cation, which either expands or contracts the lattice, in analogy to externally applied pressure. We apply positive chemical pressure by substituting germanium at the B site and negative chemical pressure by substituting lead at the B site. We also consider the effect of platinum substitution, which has nominally negligible chemical pressure effects. In the ytterbium pyrochlores, we find that positive chemical pressure tunes the magnetic ground state from ferromagnetic to antiferromagnetic. Remarkably, we also find that the ytterbium pyrochlores share a ubiquitous form to their low temperature spin dynamics despite their disparate ordered states. In the terbium pyrochlores, we find that positive chemical pressure promotes ferromagnetic correlations - the opposite effect of externally applied pressure. Our studies of platinum pyrochlores reveal that platinum, while non-magnetic, is able to facilitate superexchange pathways. Thus, the magnetic ground states of the platinum pyrochlores are significantly altered from their titanate analogs. The work in this thesis highlights the delicate balance of interactions inherent to rare earth pyrochlore magnetism and shows that chemical pressure is a powerful tool for navigating their phase spaces. |
URI: | http://hdl.handle.net/11375/22014 |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Hallas_Alannah_M_2017Aug_PhD.pdf | PhD Thesis | 18.56 MB | Adobe PDF | View/Open |
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