| Περίληψη: | The muon-spin rotation (µSR) technique predominantly uses the positive muon to study a wide range of condensed matter systems exhibiting interesting physical properties such as magnetism and superconductivity. The µ−SR technique is far
less common, mainly due to the fact that the absolute asymmetry is low, and for a comparable signal-to-noise ratio of the asymmetry it needs around 36 times more decay events to be counted than for a µ+SR experiment. Despite this, µ−SR has
its uses and has seen a recent resurgence in the study of hydrogen storage and battery materials. There is a lack of suitable fitting programs for the analysis of µ−SR data. Also, the negative muon will strongly perturb its local environment when implanted into a sample, and these distortions must be accounted for. As part of this thesis, new techniques have been developed for the analysis of µ−SR data and implemented in the Windows Muon Data Analysis software package WiMDA. The software extension, dubbed Negative-WiMDA, has been tested on new experimental data obtained on graphite, MnO, and MgH2. It has facilitated the efficient subtraction of unwanted background signals and allowed the asymmetry spectra from each element of interest to be analysed in isolation. To account for the negative muon-induced perturbations, a new technique named DFT+µ− has been developed which adapts the DFT+µ+ code to include the case of a negative muon. The DFT+µ− technique developed in this thesis has been used to predict
an asymmetrical ion configuration and a Jahn-Teller distortion in MnO. In both MgH2 and LiCoO2 the static field width, ∆, resulting from the randomly oriented nuclear spins has been calculated from the new atomic positions obtained through
DFT+µ−. In addition, a layered oxyselenide, Sr2CoO2Ag2Se2, is studied with µ+SR. The Néel temperature is found to be 160.4(1) K, which is 30 K lower than that previously deduced from magnetic susceptibility measurements. A constraint for
the magnetic structure is given using DFT+µ+ and dipole field simulations.
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