Electric field-induced modification of magnetism in thin CoPd films.

Recently, M. Weisheit et al., [Science \textbf{315}, 349 (2007)] reported modification of magnetic properties of thin-film ferromagnets by applying a large electric field at the surface of a ferromagnet. For an applied voltage of -0.6 V, the coercivities of 20 {\AA} thick FePt and FePd films were changed by -4.5 and +1{\%}, respectively. Here, we report polarized neutron reflectometry measurements of the magnetization depth profile of a 180 {\AA} thick Co$_{50}$Pd$_{50}$ film immersed in an electrolyte as a function of applied electric field in an external magnetic field. The measurements were done at two values of applied electric potential of -0.6 volts and -1.2 volts and at zero volts (open-circuit potential). The applied magnetic field was 3 kG. We found a linear increase of the film magnetization with electric field. The change of magnetization occurred in the region of the film within 72 {\AA} of the electrolyte/Co$_{50}$Pd$_{50}$ interface. The magnetization of the top part of the layer is increased by 2{\%} (-0.6 V) and 3.6{\%} (-1.2 V) compared to the open circuit potential result.