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Title: Ground states in low-dimensional quantum magnets
Author: Blackmore, William J. A.
ISNI:       0000 0004 8497 5883
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2018
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The ability to control the magnetic properties of low-dimensional magnetic systems is a major aim of research in condensed matter physics. Bespoke magnetic systems have potential uses in many practical applications and experimental investigations of theoretical predictions. To achieve this goal necessitates being able to determine the magnetic properties of these systems, which can require much expense in time, money and effort. In this thesis I present a methodology that can be used for characterising the properties of powdered, low-dimensional spin-1 antiferromagnets using commercially available measurement systems. The techniques involved are able to determine the magnetic properties of powdered systems containing isolated and exchange-coupled Ni2+ ions accurately enough such that a decision on growing single-crystals or measurements requiring more complicated measurements at specialist facilities can be made. Using this method, I then characterise the magnetic properties of a family of similar Ni2+-halide-halide-Ni2+ chains which show differing magnetic behaviour linked to the different bridging ligands. It is found that single-ion anisotropy in Ni2+ octahedral environments is not just dependent on the placement but also the electronic properties of the coordinated non-magnetic ligands. Also, magnetic interactions along the Ni2+ chains are strongly influenced by the size of the bridging halide ions. The distance between adjacent ions is less important. This property was exploited to explore bond disorder in the spin-1/2 quasi two-dimensional antiferromagnet (QuinH)2Cu(ClxBr1-x)4.2H2O, which occurs due to the presence of two competing superexchange pathways with different interaction strengths. As the concentration increases from x = 0, disorder enhances quantum fluctuations which destroy long-range order before the percolation threshold is reached. This leads to multicritical points and the possible rise of a quantum Griffiths phase.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics