Neutron diffraction studies of frustrated and correlated electron systems

Edwards, Lewis 2022. Neutron diffraction studies of frustrated and correlated electron systems. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

A new algorithm for the WISH diffractometer is discussed, in particular, its utility as extended to the solution and refinement of structures from single crystal data. Further, this algorithm finds itself applicable to structural and magnetic diffuse scattering, where it allows for the presentation of combined reciprocal space data and symmetrized planes. A correspondence between short range magnetic order and plateaus of the magnetization is established in the one-dimensional Ising system, α-CoV2O6 , in which we measure the co-existence of short-range T3 and T4 orders manifest only for a non-zero component of magnetic field applied out of the easy plane. When the magnetic field is applied along the easy axis, only T3 long range order is observed. We also describe a new method for the preparation of out-of-equilibrium, monopole rich states in Dy2Ti2O7 spin ice — a pulse heating/cooling method that relies upon the high cooling power of a dry dilution refrigerator. This includes the Bluefors refrigerator at Cardiff University — in which we tested our set-up — and the E18 refrigerator at ISIS, in which we planned to conduct our investigation of the spin correlations. Prior to our measurements on the WISH diffractometer, we achieved a very fast cooling rate of 150 mK/s in Cardiff — much faster than that previously reported in previous studies where rich monopole populations were prepared. Due to factors beyond our control, however, we had to modify our set-up in order for it to work in a standard dilution insert refrigerator, which severely limited the cooling rate and thereby the density of monopoles frozen in. As a result of these restrictions, we did not observe any appreciable change to the spin correlations, as compared to the equilibrium state; consequently, we placed a lower bound on the cooling rate spin freezing transition of 9.5 mK/s before changes to the spin correlations are manifest.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	Neutron diffraction, Neutron scattering, Magnetization plateaus, Short-range order, Diffuse scattering, Crystallography, Magnetic sructure, Structural refinement, Spin ice, Mantid, Magnetic frustration, Magnetism.
Funders:	Cardiff University, PSE College
Date of First Compliant Deposit:	1 November 2022
Last Modified:	10 Jun 2023 01:52
URI:	https://orca.cardiff.ac.uk/id/eprint/153890

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