Interacting spin droplets and magnetic properties of a low-density two-dimensional electron gas

Abstract

We argue that the magnetic susceptibility data for the low-density two-dimensional (2D) silicon-based electron gas indicate that magnetically active electrons are localized in spin droplets. The droplets exist in both the insulating and metallic phases, and interact ferromagnetically, forming an effective 2D Heisenberg ferromagnet. Comparing the data with analytical and numerical results for a 2D Heisenberg ferromagnet, we determine parameters of the model and show that the value of the droplet spin is either $S=1/2$ or $S=1$ with very few electrons in the droplet. We discuss the dependence of the magnetic susceptibility and the specific heat on the external magnetic field, which follows from the model, and hence we suggest further experimental tests of the model.