Theory of Disordered Magnets

摘要: Studying magnetic properties of disordered alloys is important both for the understanding phase transformations in and from point view fundamental issues magnetism solids. Disorder a system can result unconventional structures, such as spin glass, which have rather peculiar features.In this Thesis, general approach to studying first principles presented. Phase behavior crystalline substitutional are considered. This exemplified by calculations an archetypical spin-glass material: CuMn alloy.First, theoretical framework description thermodynamics given. It shown that under certain conditions, complex be reduced effective containing no degrees freedom. substantially simplifies investigation alloys. The model described terms material-specific interaction parameters.It parameters obtained ground-state property alloy turn calculated means highly accurate up-to-date numerical techniques based on Green's function method. subsequently used thermodynamic Monte-Carlo simulations produce atomic structures alloy. An example Cu-rich demonstrated structure presented agrees very well with results neutron-scattering experiments system. Moreover, enable one predict ground state alloy, difficult observe experiment due large diffusion barriers at temperatures close temperature transformation.A glass given, difficulties modeling type systems discussed. To overcome difficulties, improved methods, parallel tempering, overrelaxation technique, finite-size scaling method analysis, introduced.