Thermodynamics of 3He solid monolayers in the Heisenberg model

Abstract

The two-dimensional Heisenberg model is applied to the interpretation of the experimental data on the thermodynamic and magnetic properties of 3He monoatomic films in the millikelvin temperature range, i.e., under conditions when these properties are completely governed by the dynamics of the nuclear spin subsystem. The theoretical results obtained make it possible to describe the internal energy E, the heat capacity Cs, and the magnetic susceptibility χ of the two-dimensional spin-1/2 Heisenberg ferromagnets and antiferromagnets on a triangular lattice within the unified approach over the entire range of temperatures. The data available in the literature on the heat capacity and magnetic susceptibility of 3He films are interpreted in the framework of the advanced theory. Most attention is concentrated on the layers characterized by the ferromagnetic exchange. Comparative analysis of theoretical and experimental data is carried out with the use of two fitting parameters: the exchange interaction constant J and the number of “active” spins n2 in the layer that is determined from the entropy of the system in the limit T → ∞. It is demonstrated that, for the ferromagnetic layers, the theoretical results obtained within the Heisenberg model are in very good agreement with the experimental data reported by different authors.