Strong clamping of the ferromagnetic transition in epitaxial Er

We report the magnetization behavior of single-crystal epitaxial films of Er lattice matched to YxLu1-x alloy substrates. As the Er is largely strain-free, the main epitaxial constraint on its ferromagnetic transition arises solely from the interaction of the magnetostriction with the clamping effect of epitaxy. We observe large modifications of the magnetic behavior which establish that the clamping effect is large. The very different epitaxial behaviors of Dy and Er are explained in terms of accessible domain structure.