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2024-12-05T21:50:53Z urn:hdl:10459.1/57342 Magnetotransport properties of NiFe-Ag granular alloys: origin of the thermal behavior Badia Pascual, Ferran Batlle, X. Labarta, A. Watson, M. L. Johnston, A. B. Chapman, J. N. The effect of the temperature and magnetic field on the giant magnetoresistivity ~GMR! of two FeNi–Ag granular alloys of composition Fe11.4Ni6.4Ag82.2 and Fe7.6Ni16.4Ag76.0 is discussed. Both samples were prepared by rf magnetron sputtering. Parts of them were rapidly annealed at 600, 650, and 750 °C. All samples displayed giant magnetoresistivity which decays from its maximum value with a Tm behavior, with m'0.8– 0.9, suggesting that the decrease in the maximum magnetoresistivity is due to the reduction in the particle magnetization associated with the spin wave excitation, which is a different mechanism to the electron-magnon interaction responsible for the T dependence of GMR in magnetic multilayers. Magnetoresistivity r M decreases with temperature sharing essentially the same temperature decrease as the square of the macroscopic magnetization M in the whole magnetic field range studied, which is due to the reduction in the particle magnetization and to superparamagnetic effects. The effect of the width of the particle size distribution and interparticle interactions on the linear relation r M vs M2 are discussed. Care should be taken when representing r M /r(T,H50) vs (M/Ms)2 because the strong temperature-dependent slope shown in these plots is mainly due to the temperature dependence of both the resistivity r(T,H50) and Ms , and it is not an intrinsic T dependence of GMR in granular alloys. Experimental results suggest that in granular materials, magnetoresistivity is dominated by magnetic moments at the surface of the particles, which also play a very important role in the demagnetization processes, and small magnetic particles. Financial support of both the Spanish CICYT through the MAT94-1024-CO2-02 Project and the Catalan CIRIT through the GRQ1012 Project (1993–96) are largely recognized. 2024-12-05T21:50:53Z 2024-12-05T21:50:53Z 2016-07-04T10:37:34Z 2016-07-04T10:37:34Z 1997 article publishedVersion http://hdl.handle.net/10459.1/57342 Reproducció del document publicat a https://doi.org/10.1063/1.365598 Journal of Applied Physics, 1997, vol. 82, núm. 2, p. 677-687 (c) American Institute of Physics, 1997 info:eu-repo/semantics/openAccess American Institute of Physics