Properties of magnetic nano-particles

Publication: Research - peer-reviewJournal article – Annual report year: 1997

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The intrinsic thermodynamic magnetic properties of clusters are discussed using spin wave theory for a Heisenberg model, with a fixed magnitude of the spins S-i = S and site independent nearest neighbor exchange interaction. The consequences of the more realistic Hubbard model is considered in which we allow for a magnetization profile at T = 0 and a structural relaxation, which in turn will give rise to a site dependent exchange interaction. Et is concluded that correlation effects among the electrons play a very important role in small clusters, albeit not modifying the thermodynamic properties drastically. The finite cluster size gives foremost rise to a discrete excitation spectrum with a large energy gap to the ground state. The relaxation of the magnetization during the reversal of the external magnetic field is discussed. A first step towards a quantitative understanding of the nonequilibrium statistical mechanics in single-domain ferromagnetic particles is a systematic study of the kinetic Ising model. Results from Monte Carlo simulation and droplet theory are reviewed with particular attention to the effects of various boundary conditions, including a decrease in the number of surface bonds and an addition of surface anisotropy. A new dynamic ''outside-in'' flip mode is proposed.
Original languageEnglish
JournalActa Physica Polonica A
Issue number1
Pages (from-to)121-133
StatePublished - 1997
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ID: 6604276