Critical Casimir forces for a particle between two planar walls

Abstract We consider a cube placed between two planar surfaces bounding a three-dimensional Ising slab. This system can be viewed as the magnetic analog of a colloidal particle immersed in a fluid, which is confined by two parallel walls. Near the bulk critical point of the Ising ferromagnet the cube gets exposed to the potential of the fluctuation that induces the critical Casimir force. Using Monte Carlo simulations we study the dependence of this potential on the relative boundary conditions at the two surfaces and at the cube within a wide range of temperatures above and below the bulk critical temperature. In order to calculate the critical Casimir force and its potential, we adopt an approach based on an integration scheme of free energy differences. The scaling functions of the corresponding critical Casimir forces are also determined.