  Triggered by the revival of multiferroic materials, a lot of effort is
presently undergoing as to find a coupling between a capacitance and a magnetic
field. We show in this report that interfaces are the right way of increasing
such a coupling provided free charges are localized on these two-dimensional
defects. Starting from commercial diodes at room temperature and going to grain
boundaries in giant permittivity materials and to ferroelectric domain walls, a
clear magnetocapacitance is reported which is all the time more than a few
percent for a magnetic field of 90kOe. The only tuning parameter for such
strong coupling to arise is the dielectric relaxation time which is reached on
tuning the operating frequency and the temperature in many different materials.
