Quantum mechanical description and interpretation of nanomagnets

Zadatak ovog završnog rada je kvantno-mehanički opis dinamike spina u nanomagnetima, te tumačenje pojava koje se javljaju na nanometarskoj skali magnetskih čestica. Matematički opis dinamike spina sadržava tri glavne teoretske jednadžbe: Bloch jednadžba, Landau-Lifshitz jednadžba, te Landau-Lifshitz-Gilbert jednadžba dinamike spina. Na primjerima jednomolekulskog magneta Mn12-acetata, nanočestica CuFe2O4 i Cu0.5Fe2.5O4, te amorfne nanoslitine Hf57Fe43 objašnjene su pojave klasične i kvantne magnetske relaksacije, tuneliranja spina, magnetskih domena, te utjecaj kemijske strukture tih čestica na njihova fizikalna svojstva. Na temelju mjerenja magnetskog momenta tokom hlađenja u magnetskom polju i bez magnetskog polja, određene su krivulje histereze pojedinog sustava. Iz rezultata tih mjerenja, zaključuju se uzroci pojedinih oblika krivulje i očitavaju karakteristične vrijednosti za dani primjer.The primary goal of this thesis is a quantum-mechanical description of spin-dynamics in nanomagnets, and the interpretation of phenomena relating general nano-scale events in magnetic particles. Mathematical description of spin mechanics is done through three main theoretical equations: The Bloch-equation, Landau-Lifshitz equation and Landau-Lifshitz-Gilbert equation. Examples of single-molecule magnets such as Mn12-acetate, nanoparticles CuFe2O4 i Cu0.5Fe2.5O4, and amorphous nano-alloys Hf57Fe43 are given, to explain classical and quantum magnetic relaxation phenomenon, spin thermal activation and quantum tunnelling, magnetic domains and the general influence of chemical structure on certain physical properties. Based on magnetic moment measurement results, hysteresis-loops for each system were acquired. Those results lead towards conclusion of causes behind curve-shape details, and enable notification of specific system characteristics