  The Curie temperature is one of the most fundamental physical properties of
ferromagnetic materials and can be described by Weiss molecular field theory
with the exchange interaction of neighboring atoms. Recently, the
electric-field-induced modulation of the Curie temperature has been
demonstrated in transition metals. This can be interpreted as indirect evidence
for the electrical modulation of exchange coupling. However, the scenario has
not yet been experimentally verified. Here, we demonstrate the electrical
control of exchange coupling in cobalt film from direct magnetization
measurements. We find that the reduction in magnetization with temperature,
which is caused by thermal spin wave excitation and scales with Bloch's law,
clearly depends on the applied electric field. Furthermore, we confirm that the
correlation between the electric-field-induced modulation of the Curie
temperature and that of exchange coupling follows Weiss molecular field theory.
