Surface magnetism of gallium arsenide nanofilms

Gallium arsenide (GaAs) is the widest used second generation semiconductor with a direct band gap and increasingly used as nanofilms. However, the magnetic properties of GaAs nanofilms have never been studied. Here we find by comprehensive density functional theory calculations that GaAs nanofilms cleaved along the and directions become intrinsically metallic films with strong surface magnetism and magnetoelectric (ME) effect. The surface magnetism and electrical conductivity are realized via a combined effect of transferring charge induced by spontaneous electric-polarization through the film thickness and spin-polarized surface states. The surface magnetism of nanofilms can be significantly and linearly tuned by vertically applied electric field, endowing the nanofilms unexpectedly high ME coefficients, which are tens of times higher than those of ferromagnetic metals and transition metal oxides.