Two-dimensional nuclear magnets

We review in this paper the experimental results on two-dimensional nuclear magnetic systems obtained by physical adsorption of He-3 atoms on solid substrates. Two-dimensional nuclear antiferromagnets and ferromagnets have been observed and studied in recent years, providing useful model systems for spin 1/2 magnetic Hamiltonians and leading to results of general validity on the magnetic ordering of two-dimensional spin systems. Heisenberg, multiple spin and Rudermann-Kittel exchange as well as vacancy-induced magnetism are discussed in the context of the experimental investigations of adsorbed He-3 films.