Domain formation in hollow spherical Invar nano-particles
Monte Carlo simulations were performed on the hollow spherical geometry of binary Invar alloy based on a model with a localized spin Hamiltonian taking into account the occurrence of high-spin (HS) and low-spin (LS) states for the atomic magnetic moments of one of its components. When heating the system from its ferromagnetic ground state to above the Curie temperature and then subsequent cooling, domain formation is observed, which is not expected for particles of this size. The domains consist of HS atoms surrounded by LS atoms. Since the LS atoms do not interact magnetically, the alignment of spin moments between regions of HS atoms are independent of each other and thus there is a reduced contribution to the total magnetic moment, resulting in a decrease in the magnetization of the system. Reduction of the total magnetic moment in this geometry is size and thickness dependent.
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