Magnetic phases in ultrathin helimagnetic holmium films

Detailed Monte Carlo simulations of Ho magnetic thin films are here presented. The system is described by a Heisenberg model with easy-plane single-ion anisotropy and seven coupling constants, as obtained by experimental neutron scattering measurements. The critical behavior landscape comes out extremely complex and fascinating. In fact, for the analyzed thicknesses of 8-16, it is seen that by increasing the temperature the films show, after the distorted helical configuration, a temperature range where disordered inner planes coexist with surface ones in a block ordered state. At low temperature, it is also found that the progressive reduction in the number of layers do not imply a sudden helical order suppression but rather, as a consequence of surface effects, a gradual passage to a fanlike order, accompanied by the helix distortion, is observed. (C) 2009 American Institute of Physics.