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Title: Spin and lattice structures in materials with competing interactions investigated by neutron scattering techniques
Author: Shen, Lingjia
ISNI:       0000 0004 5994 6212
Awarding Body: University of Birmingham
Current Institution: University of Birmingham
Date of Award: 2016
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Three magnetic materials, including γ-CoV\(_2\)O\(_6\),Pr\(_0\)\(_.\)\(_5\)Ca\(_0\)\(_.\)\(_5\)Mn\(_0\)\(_.\)\(_9\)\(_7\)Ga\(_0\)\(_.\)\(_0\)\(_3\)O\(_3\), and Y\(_2\)(Cr\(_1\)\(_-\)\(_χ\)Ga\(_χ\)\(_-\)\(_0\)\(_.\)\(_5\)Sb\(_0\)\(_.\)\(_5\))\(_2\)O\(_7\)(χ = 0.5, 0.6, 0.7, 0.8, 0.9), in which the magnetic or crystallographic structure shows strong correlations with the competing interactions (e.g. electron-lattice coupling, spin exchange interactions, single-ion anisotropy), have been explored by the neutron diffraction and small angle neutron scattering techniques. For the quasi-one-dimensional magnet γ-CoV\(_2\)O\(_6\), our neutron diffraction measurements have revealed a spatially inhomogeneous magnetic ground state, i.e. phase separation, below T\(_N\) = 6.6 K. For the strained manganese perovskite Pr\(_0\)\(_.\)\(_5\)Ca\(_0\)\(_.\)\(_5\)Mn\(_0\)\(_.\)\(_9\)\(_7\)Ga\(_0\)\(_.\)\(_0\)\(_3\)O\(_3\), we have observed the decoupling of magnetic field induced carrier delocalization and para-ferromagnetic transitions. Concomitantly, distinct responses of the crystallographic structure to these two transitions have also been established. For the diluted pyrochlores Y\(_2\)(Cr\(_1\)\(_-\)\(_χ\)Ga\(_χ\)\(_-\)\(_0\)\(_.\)\(_5\)Sb\(_0\)\(_.\)\(_5\))\(_2\)O\(_7\), we cannot detect any magnetic long range order in Y\(_2\)CrSbO\(_7\) (χ = 0.5), although it is well below the nonmagnetic site percolation limit (χ\(_c\) = 0.61). We propose that the magnetism of Y\(_2\)CrSbO\(_7\) is governed by the bond disorder, caused by the weak ionic size mismatch between Cr\(^3\)\(^+\) and Sb\(^5\)\(^+\) and percolates at χ = 0.24, so that a spin-freezing transition is expected at very low temperatures according to the latest spin glass theories.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics