Master thesis defense by Morten Haubro
In this thesis I describe the design process of a uniaxial pressure cell for use in neutron scattering experiments. The cell is optimized for measuring the broad and diffuse magnetic scattering signals that are characteristic of magnetically frustrated compounds. Furthermore, the room temperature and low temperature calibration, of a load gauge for in situ pressure determination, is presented. Neutron measurements demonstrate that the pressure cell has a homogeneous and largely non-magnetic background. The result is a pressure cell with in-situ pressure determination, accurate within 10 %, that is functional up to 3 GPa.
Neutron experiments are performed on the spin ice material Ho2Ti2O7 under uniaxial pressure. Spin ice materials gained interest in the late 20th century for their substantial zero-point entropy and the apparent emergence of magnetic monopole excitations. Previous work has shown that the magnetic susceptibility of the very similar Dy2Ti2O7 has a significant pressure response. New theoretical work suggest that this response is a result of the uniaxial pressure lifting the ground state degeneracy, reducing the size of the ground state manifold.
I show results that, with low statistical significance, are consistent with theory. The peak intensity of the spin flip scattering shows an increased intensity of 4 ± 4 %. Furthermore, the pinch point scattering shows a significant increase as a function of pressure. This change is not predicted by the theoretical model.
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Topic: Morten Haubro defence
Time: Dec 15, 2020 09:00 AM Copenhagen
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