Microscopic origin of electric-field-induced modulation of Curie temperature in cobalt

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.