Shen, Lingjia (2016). Spin and lattice structures in materials with competing interactions investigated by neutron scattering techniques. University of Birmingham. Ph.D.
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Shen16PhD.pdf
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Abstract
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.
Type of Work: | Thesis (Doctorates > Ph.D.) | ||||||
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Award Type: | Doctorates > Ph.D. | ||||||
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College/Faculty: | Colleges (2008 onwards) > College of Engineering & Physical Sciences | ||||||
School or Department: | School of Physics and Astronomy | ||||||
Funders: | None/not applicable | ||||||
Subjects: | Q Science > QC Physics | ||||||
URI: | http://etheses.bham.ac.uk/id/eprint/7045 |
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