The dielectric and magnetic properties of electric double layer (EDL) capacitor structures\nwith a perpendicularly magnetized Pt/Co/Pt electrode and an insulating cap\nlayer (MgO) are investigated. An electric field is applied through a mixed ionic liquid/\nMgO barrier to the surface of the top Pt layer, at which the magnetic moment\nis induced by the ferromagnetic proximity effect. The basic dielectric properties of\nthe EDL capacitor are studied by varying the thickness of the MgO cap layer. The\nresults indicate that the capacitance, i.e., the accumulated charge density at the Pt\nsurface, is reduced with increasing the MgO thickness. From the MgO thickness\ndependence of the capacitance value, the effective dielectric constant of the ionic\nliquid is evaluated. Almost no electric field effect on the magnetic moment, the coercivity,\nor the Curie temperature is confirmed in the top Pt layer with the thickness of\n1.3 nm, regardless of the presence or absence of the MgO cap layer, whereas the a\nclear change in the magnetic moment is observed when the top Pt layer is replaced\nby a Pd layer of 1.7 nm.
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