Europhys. Lett.
Volume 70, Number 3, May 2005
Page(s) 348 - 354
Section Condensed matter: structural, mechanical and thermal properties
Published online 08 April 2005
Europhys. Lett., 70 (3), pp. 348-354 (2005)
DOI: 10.1209/epl/i2005-10009-3

A new boundary-controlled phase transition: Phase separation in an Ising bi-pyramid with competing surface fields

A. Milchev1, 2, M. Müller1, 3 and K. Binder1

1  Institut für Physik, WA331, Johannes Gutenberg-Universität 55099 Mainz, Germany
2  Institute for Physical Chemistry, Bulgarian Academy of Sciences 1113 Sofia, Bulgaria
3  Department of Physics, University of Wisconsin-Madison 1150 University Avenue, Madison, WI 53706-1390, USA

received 1 February 2005; accepted in final form 18 March 2005
published online 8 April 2005

We study phase coexistence of an Ising ferromagnet in a bi-pyramid geometry with a square basal plane of linear extension 2L+1. Antisymmetric surface fields act on the pyramid surfaces above and below the basal plane. In the limit $L\rightarrow\infty$, the magnetisation stays zero at the bulk critical temperature, but becomes discontinuously non-zero at the cone filling critical temperature associated with a single pyramid. Monte Carlo simulations and scaling considerations show that this transition is described by a Landau theory with size-dependent coefficients that give rise to singular critical amplitudes.

68.08.Bc - Wetting.
05.70.Fh - Phase transitions: general studies.
68.35.Rh - Phase transitions and critical phenomena.

© EDP Sciences 2005