Magnetocapacitance and surface magnetism in Pd/Fe/Pd trilayer structures*

For sufficiently thin insulator spacing in metal-insulator-metal (M-I-M) trilayer structures, the capacitance can be dominated by the interface of the dielectric and the electrodes. If one or both of the electrodes are ferro- or paramagnetic, the screening length is influenced by a difference in the spin-up and spin-down densities of states, and the resulting magnetic-field induced changes in capacitance (magnetocapacitance) become a sensitive measure of surface magnetism. We have grown Pd (200 {\AA})/Fe~(1.5 {\AA})/Pd ($x~${\AA}) trilayer structures, where $x$ was varied from 50~{\AA} to 2~{\AA}. All of the films are ferromagnetic having similar saturation magnetizations at 10~K. However, as $x$ is decreased, there is a significant increase in the coercive field ($H_{c})$ from $H_{c}\sim $7~Oe for $x$~=~50~{\AA} to $H_{c}\sim $30~Oe for $x$~=~2 {\AA}. The sensitivity of magnetic properties to the proximity of the interface reflects a cross over from bulk to surface-dominated magnetism. We will correlate this crossover with magnetocapacitance measurements on M{\-}I{\-}M capacitors where the Pd/Fe/Pd trilayer is the base electrode and $x$ is the separation of the Fe layer from the interface with the dielectric of the capacitor.