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|Title:||Fragile magnetism in rare earth XY pyrochlores|
|Advisor:||Gaulin, Bruce D.|
|Abstract:||The topic of investigation in this thesis is the pyrochlore titanates A2Ti2O7 where A3+ is a magnetic rare earth ion and Ti4+ is non-magnetic. The pyrochlore is a cubic structure composed of two inter-penetrating networks of corner-sharing tetrahedra and is the archetypal platform for the study of magnetic frustration in three dimensions. Magnetic frustration in rare earth pyrochlores favors the stabilization of various exotic magnetic phenomena such as the classical and quantum spin liquid states. The degree of magnetic frustration in these systems depends strongly on the local spin anisotropy of the rare earth ion. In this thesis, we studied the magnetic properties of XY pyrochlore magnets where the spins have a preference to point perpendicular to the centers of the two tetrahedra they connect. XY local anisotropy is obtained in the rare earth pyrochlores Yb2Ti2O7 and Er2Ti2O7, which are the primary subjects of this thesis. Using elastic and inelastic neutron scattering techniques, we study the magnetic ground state of Yb2Ti2O7 and Er2Ti2O7 as a function of various perturbations such as disorder, dilution, hydrostatic pressure and chemical pressure. Our results on Yb2Ti2O7 reveal a spin liquid ground state at ambient pressure. The spin liquid state of Yb2Ti2O7 is found to be unstable upon the application of hydrostatic pressure, from which a ferromagnetic ground state is obtained. Er2Ti2O7 is known to magnetically order into an antiferromagnetic 2 state at 1.2 K. Diluting the Er3+ site with non-magnetic Y3+ ions causes a transition from the 2 antiferromagnetic state found in Er2Ti2O7 to a frozen mosaic of psi2 and psi3 at a critical dilution of about 20%-Y. Furthermore, it will be demonstrated that Er2Ti2O7 has a rich phase diagram in both an applied magnetic field as well as with the application of chemical pressure. The fragile magnetism in both Yb2Ti2O7 and Er2Ti2O7 is discussed in terms of multiphase competition that promotes spin liquid behaviour and order-by-disorder phenomena.|
|Appears in Collections:||Open Access Dissertations and Theses|
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