Zero field resistance dip in magnetic tunnel junctions employing a granular electrode

We present magnetoresistance (MR) measurements performed on magnetic tunnel junctions in which one of the electrodes is a continuous Ni film and the other is a granular Ni film. These junctions exhibit a zero field resistance dip followed by a large-field negative MR. The dip magnitude depends on the granular electrode fabrication details. We interpret these results as a consequence of orange peel coupling between the continuous ferromagnetic film and the magnetic grains. Apart from the uniqueness of the positive MR, this experiment provides an opportunity to study the orange peel effect in structures involving magnetic grains.