An experimental investigation of the magnetic and structural properties
of Ni2FeGa, Ni51Fe22Ga27 and Ni2MnGa0.95Sn0.05 is reported.
The structure of the compounds has been characterised using X-ray
diffraction at Loughborough University and neutron diffraction at
the Institut Laue-Langevin (ILL), Grenoble. At room temperature
Ni51Fe22Ga27 and Ni2MnGa0.95Sn0.05 show a single phase Heusler
structure with space group Fm3m which transforms to an orthorhombic
martensitic phase below the transition temperature. In contrast
Ni2FeGa exhibits an additional f.c.c. phase at high temperature. The
low temperature structure of Ni51Fe22Ga27 was found to be completely
different to the structure of other shape memory alloys investigated so
far, e.g. Ni2MnGa. The results for the Ni–Fe–Ga compounds presented
in this thesis are in contrast to recently published investigations.
Magnetisation, specific heat and resistivity measurements have been
carried out to determine the martensitic phase transition temperatures.
All compounds investigated exhibit a first order transition accompanied
by a hysteresis far below room temperature. A martensitic
phase transition is essential for shape memory behaviour.
A Master's Thesis. Submitted in partial fulfilment of the requirements for the award of Master of Philosophy at Loughborough University.