Based on the Stoner Model for a single band in the mean field approximation (MFA),
aspects of the interaction between lattice deformation and magnetisation of itinerant
electron systems are studied.
The derivation of the Hartree–Fock–Stoner (HFS) Hamiltonian is reviewed for a single
band starting from a general Hamiltonian describing band electrons. The finite-temperature
properties of the model, including the various magnetic states and the ferromagnetic-to-paramagnetic phase transition, are briefly discussed within MFA.
The HFS Hamiltonian is applied to a single band with a rectangular density of states
(DOS). The finite temperature magnetic properties of the system are studied using MFA.
The model is extended to incorporate the interaction of lattice and magnetic degrees of
freedom by introducing a dependence of the bandwidth on the lattice parameter. The
effects of local variations of the lattice parameter are studied by introducing a local
bandwidth and treating the variations as fluctuations. The results are compared to
experimental magnetisation measurements of Invar alloys. Furthermore, magnetostriction
and magnetic contributions to the thermal expansion are discussed within the model.
Finally, effects of particle exchanges are considered within the model.
A Master's Thesis. Submitted in partial fulfilment of the requirements for the award of Master of Philosophy at Loughborough University.