  Effects of the Verwey transition on the (100) surface of magnetite were
studied using scanning tunelling microscopy and spin polarized low-energy
electron microsccopy. On cooling through the transition temperature Tv, the
initially flat surface undergoes a roof-like distortion with a periodicity of
~0.5 um due to ferroelastic twinning within monoclinic domains of the
low-temperature monoclinic structure. The monoclinic c axis orients in the
surface plane, along the [001]c directions. At the atomic scale, the
charge-ordered sqrt2xsqrt2R45 reconstruction of the (100) surface is
unperturbed by the bulk transition, and is continuous over the twin boundaries.
Time resolved low-energy electron microscopy movies reveal the structural
transition to be first-order at the surface, indicating that the bulk
transition is not an extension of the Verwey-like sqrt2xsqrt2R45
reconstruction. Although conceptually similar, the charge-ordered phases of the
(100) surface and sub-Tv bulk of magnetite are unrelated phenomena.
