Vacancy-Induced Ferromagnetism: The Registered Phase ofHe3on Grafoil

Abstract

Submonolayer ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ on Grafoil at density $n$ just below the density of the registered phase, $n_c$, corresponds to a low-density solid with vacancy concentration $\frac{(n_c-n)}{n_c}$. Under suitable circumstances, these vacancies cause the solid to undergo a ferromagnetic transition.