Polarized neutron scattering signatures of classical spin ice

• Main Author: Goh, Jeremy Swee Kang
• Other Authors: Christos Panagopoulos
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: DRNTU::Science::Physics::Electricity and magnetism
• Online Access: http://hdl.handle.net/10356/76435
• Institution: Nanyang Technological University

Almost a decade ago, it was proposed by Fennell et al. that polarized neutron scattering could expose the dipolar spin correlations in the classical spin ice Ho2Ti2O7, in which its sharp, distinctive “pinch-point” signatures would appear exclusively in the spin-flip (SF) neutron scattering channel, and not in the non-SF (NSF) channel. In the same work, they showed via Monte Carlo simulations that the NSF of the nearest-neighbour (NN) spin ice, excluding the magnetic form factor, is completely featureless (i.e., no dispersions) in the (hhl) scattering plane. However, no explanation was offered by the authors for this particular observation, and this has been largely overlooked in the literature since then. In this thesis, we endeavoured to understand the origins of NSF scattering patterns (or rather, lack thereof) for classical spin ice using a combination of analytical techniques and numerical simulations. We propose two ways of understanding this phenomenon: 1) as a manifestation of the flat bands within the framework of the large-n approximation, or 2) vanishing real space correlations between chains in the pyrochlore lattice. The relevance of the flat bands to featureless NSF is exposed via analysis of the large-n matrix, while the latter is supported by Monte Carlo simulation results.