  We have measured quantum transport through an individual Fe$_4$
single-molecule magnet embedded in a three-terminal device geometry. The
characteristic zero-field splittings of adjacent charge states and their
magnetic field evolution are observed in inelastic tunneling spectroscopy. We
demonstrate that the molecule retains its magnetic properties, and moreover,
that the magnetic anisotropy is significantly enhanced by reversible electron
addition / subtraction controlled with the gate voltage. Single-molecule
magnetism can thus be electrically controlled.
