Scanning tunneling microscope images of the (100) surface of slightly
nonstoichiometric magnetite taken at room temperature show static arra
ys of pairs of Fe2+ ions with short-range order, and a charge fluctuat
ion time greater than 10(3) s. The surface appears to be a Wigner glas
s with electron pairs localized on adjacent ions as the basic unit. Th
e explanation of Wigner localization at room temperature on the surfac
e only is that the spin-polarized minority-spin band derived from d(yz
) orbitals is stabilized and narrowed by the absence of an apicial oxy
gen from the B-site octahedron. This leads to surface anisotropy where
the Fe2+ spins are pinned normal to the {100} surfaces. Surface aniso
tropy is expected to outweigh bulk anisotropy in submicron particles.