Ferromagnetic nanoclusters in two-dimensionalHe3

Abstract

$^{3}\mathrm{He}$ adsorbed on graphite is an almost ideal two-dimensional (2D) fermionic system. The 2D solid, where the interaction between the nuclear spins $S=\frac{1}{2}$ is due to multiple spin exchange, has been extensively studied as a model system for strongly interacting fermions in 2D. At high densities in the second layer, three-body exchange dominates and leads to Heisenberg ferromagnetism. We report on nuclear magnetic resonance measurements at ultralow temperatures and low magnetic fields of the second layer of $^{3}\mathrm{He}$ on graphite preplated by one layer of $^{4}\mathrm{He}$. By adding controlled amounts of $^{4}\mathrm{He}$, $^{3}\mathrm{He}$ atoms are pushed out from the ferromagnetic domains, which become smaller and denser. We can evaluate the properties of these clusters, and control their size from a few tens to a few hundreds of atoms. These sizes are comparable to today's computing capabilities for exact numerical calculations on small clusters, and should lead to direct comparison between measurements on this model Heisenberg system and theory.