Magnetocapacitance: A probe of spin dependent potentials

We have measured the magnetic field dependence of the capacitance of Pd-AlOx-Al thin film structures. The AlOx dielectric is thin enough to ensure that the capacitance is dominated by screening effects in the electrodes. The observed quadratic dependence of capacitance on magnetic field is consistent with a theoretical model that includes the effect of a spin-dependent electrochemical potential on electron screening in the paramagnetic Pd. This spin-dependent electrochemical potential is related to the Zeeman splitting of the narrow d-bands in Pd. The application of a magnetic field increases the screening length, which is consistent with our observed negative magnetocapacitance.