Magneto-elastic coupling within the Stoner model
thesisposted on 19.09.2018, 13:53 by Stefan J. Hilbert
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.
Friedrich Naumann Foundation.