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Phase transitions in nanosystems caused by interface motion: The Ising bi-pyramid with competing surface fields

A. Milchev·M. Mueller·K. Binder
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Abstract

The phase behavior of a large but finite Ising ferromagnet in the presence of competing surface magnetic fields +/- H_s is studied by Monte Carlo simulations and by phenomenological theory. Specifically, the geometry of a double pyramid of height 2L is considered, such that the surface field is positive on the four upper triangular surfaces of the bi-pyramid and negative on the lower ones. It is shown that the total spontaneous magnetization vanishes (for L -> infinity) at the temperature T_f(H), related to the "filling transition" of a semi-infinite pyramid, which can be well below the critical temperature of the bulk. The discontinuous vanishing of the magnetization is accompanied by a susceptibility that diverges with a Curie-Weiss power law, when the transition is approached from either side. A Landau theory with size-dependent critical amplitudes is proposed to explain these observations, and confirmed by finite size scaling analysis of the simulation results. The extension of these results to other nanosystems (gas-liquid systems, binary mixtures, etc.) is briefly discussed.

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A. Milchev, M. Mueller, K. Binder. 2005-09-06. Phase transitions in nanosystems caused by interface motion: The Ising bi-pyramid with competing surface fields. https://doi.org/10.1103/physreve.72.031603

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