Origin of giant magnetoresistance effect in granular thin films

Abstract

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.

Magnetic Anisotropy and Magnetoresistance Properties of Co/Au Multilayers

“…This case is different, for example, for the isotropic multilayers [37], [38], where the MR is independent of the measuring dirrections of H or I . Since the effective MR arises from the combination of the GMR and AMR contributions, the observed differences in MR between H ⊥ I and H I configurations can be explained by considering the dependence of GMR and AMR on the orientations of H and I .…”

Giant Magnetoresistance and Related Properties of Rare-Earth Manganates and Other Oxide Systems

“…53 The importance of such superparamagnetism in the GMR of granular metallic films has also been pointed out. 54…”

Evidence of giant magnetoresistance effect in heterogeneous nanogranular films produced by ultrashort pulsed laser deposition

“…Even though the full investigation of the properties of these innovative NPs films deserves a deeper future work, the behaviour and intensity of the magnetoresistance cycles, particularly at applied fields higher than 1 T, can actually permit to conjecture a GMR effect produced by either very small nanogranules (<3 nm) dispersed through the larger, oblate ones (Maeda et al, 1994;Milner et al, 1999), or the presence of small magnetically disordered regions -with dimensions comparable to the electron mean free path and the spin diffusion length (namely the mean free path between two sequential spin flip scattering events) -on the NPs surface (Allia et al, 2006;Barlett et al, 1994;Vavassori et al, 2003;Bellouard et al, 1994). Both these conjectures appear to be coherent with the strong difference between GMR and magnetization hysteresis loops observed in these uPLD films (Iannotti et al, 2007).…”