Mössbauer spectroscopy of some magnetic materials
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Results from investigations of small amounts of ⁵⁷Fe in NiCl₂, NiBr₂, Nil₂, Col₂, α -MnS, MnSe and Mg0.15 Mn0.83 Se using Mössbauer spectroscopy are reported. In most of these compounds the results are satisfactorily analysed by a crystal field model, and new information concerning their magnetic spin arrangements has been obtained. At all temperatures below TN for NiCl₂ + ⁵⁷Fe, and at temperatures between TN and 23 K for NiBr₂ + ⁵⁷Fe, the spins are directed along a hexagonal <210> direction. Below 23 K, the Hossbauer results from NiBr₂ + ⁵⁷Fe are consistent with a different magnetic structure. Optical spectra taken at several temperatures suggest that Fe impurities modify the NiBr₂ helical arrangement. Mossbauer spectra of NiI₂ + ⁵⁷Fe show extreme line broadening at T < TN; possible explanations are discussed. In CoI₂ + ⁵⁷Fe the results are consistent with a magnetic structure in which the spins lie in the basal plane. The results from α-MnS show that there are at least two magnetic arrangements. At 131 K < T < TN the spins are along a cubic <110> direction, and below 117 K a multiaxial arrangement is likely. A detailed account of the low temperature crystallographic and magnetic behaviour of MnSe + ⁵⁷Fe is given. At certain temperatures two different crystallographic structures coexist. In the NaCl form, the spin arrangement appears to be multiaxial. The other form is a NiAs modification in which the spins are pointed along a hexagonal <210> direction. In order to check whether the concentration of Fe affects the conclusions, two different ⁵⁷Fe concentrations were used in MnSe and also in NiI₂. Attempts to prepare β-MnS + ⁵⁷Fe and MnTe + ⁵⁷Fe are described.