Though the demagnetization process of granular Co-Ag lilms became steep by adding permalloy layer> slow saturation in the magnetoresistance (MR) curves was maintained. In addition, the MR characteristics of granular Fe-Ag films prepared under a magnetic field, in which strong magnetic anisotropy was induced, were isotropic. The disagreement between the MR and magnetic characteristics implies that ferromagnetic granules are not responsible for the giant MR (GMR) effect. The MR ratio of the granular Fe-Ag films considerably increased at thicknesses less than 20 mn. In such ultrathin lilms, the features of the MR curves corresponded well with those of the magnetization curves with slow saturation and no hysteresis. These results suggest that the GMR effect in the granular systems is attributable to superparamagnetism.
FeCc-Ag thin 6l"s with a grain svucture, in which the FeCo alloy and the Ag metal are mutually insoluble, were prepared by a vacuum deposition method. The m i m u m magnetoresistance (MR) ratio observed in these 6lms was 13.0% at mom temperature in the magnetic field region between -1 and 1 T Here the features of the M R curve m-ponded well with those of the magnelization cuwe. ?his indicates the appearance of a giant MR effect in such pin-rype alloy thin films Though the magnetic anisotropy field (Hk) associated with the MR ctaracteristics that were obtained is Baremely large el T), pmper annealing was found to be mective for decreasing the Hk value without causing a drop in the MR ratio.
Granular Co–Ag films show a steep low-field magnetization process when they are covered by a permalloy layer, but their magnetoresistance (MR) curves show slow saturation. In granular Fe–Ag films prepared under a magnetic field, moreover, strong magnetic anisotropy is induced in the magnetization curves, while the MR curves are isotropic. The disagreement between the MR and magnetization curves suggests that ferromagnetic granules are not responsible for the giant MR (GMR) effect. The MR ratio of the granular Fe–Ag film is much enhanced when the thickness of the film is less than 20 nm. In such ultra-thin films, the MR and magnetization curves show slow saturation and no hysteresis. These results indicate that superparamagnetism causes the GMR effect in granular systems.
SmcNral, magnetoresistance (m), and magnetic chaacteristics were studied on FeCwAg grain-type alloy thin films annealed under various conditionr. Internal diffusion and interfacial diffusion of the Ag a" in the femmaguetic FeCo grains passessed negative and positive contributions to obtaining a large MR ratio, respectively. The magnetic anisotropy field ( H i ) associated wilh the MU characteristics decreased in accordance with the decrease in resistivity as the annealing tempemme and/or annealing time inneased. This suggests that the Ruderman-Kiltel-Kasuya-yosida interaction between the ferroma&netic grains dominates the Hk in such systems.When two kinds of metal that are mutually insoluble are evaporated or sputtered at the same time, each metal is known to individually form fine grains in the prepared film [I]. Recently, it has been observed that a giant magnetoresistance ( G m ) effect is present in such 'grain-type alloy thin films' comprising magnetic and non-magnetic metals l2-71. These results demonstrated that the G m effect is not restricted to multilayered structures and they showed that additional oppoitunities exist for technological applications. However, the magnetic anisotropy field (H,) associated with the m characteristics, which is important in the application of MR head devices, was too large in such grain systems. From our studies
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