ORIGIN OF GIANT MAGNETORESISTANCE EFFECT IN GRANULAR THIN-FILMS

Though the demagnetization process of granular Co-Ag films became stee p by adding permalloy layer, slow saturation in the magnetoresistance (MR) curves was maintained. In addition, the MR characteristics of gra nular Fe-Ag films prepared under a magnetic field, in which strong mag netic anisotropy was induced, were isotropic. The disagreement between the MR and magnetic characteristics implies that ferromagnetic granul es are not responsible for the giant MR (GMR) effect. The MR ratio of the granular Fe-AG films considerably increased at thickness less than 20 nm. In such ultrathin films, the features of the MR curves corresp onded well with those of the magnetization curves with slow saturation and no hysteresis. These results suggest that the GMR effect in the g ranular systems is attributable to superparamagnetism.