Magnetic properties of mesoscopic ultrathin magnetic films with uniaxial anisotropy

Abstract

We study magnetic properties of micron- and submicron-scale ultrathin ferromagnetic films with uniaxial anisotropy by means of a two-dimensional Ising model with both exchange and dipolar interactions using both a mean field approximation and a Monte Carlo method. We find that, in those films, the size of the surface area is an important parameter to determine their magnetic properties. In particular, we find three lattice size ranges A, B, and C. In the range A (small lattices), the model exhibits properties similar to those of a usual Ising model. In the range B (moderate lattices), the specific heat exhibits a double peak around T1 and T2 (<T1) and the magnetization increases abruptly around T2 like that in the first order phase transition. In the range C (large lattices), the magnetization does not increase but the specific heat still exhibits a double peak. In usual materials, the crossover length between the ranges A and B will be of order of submicrons. Then a special attention should be paid to their sizes for analyzing their magnetic properties.