Magnetization and magnetroresistance in Fe-ion-implanted Cu and Ag thin films

Diluted granular films of Cu-Fe and Ag-Fe (iron content < =2%) were produced using exp 57 Fe ion implantation on Cu(Ag) films previously grown by laser ablation. Conversion electron Mossbauer spectroscopy shows that the implanted Fe forms either very small clusters (up to a few atoms) or large iron alpha -phase particles. These structural characteristics directly reflect on the magnetization, which exhibits ferromagnetic-like behavior at room temperature (due to large clusters) superimposed by a significant paramagnetic contribution at low temperatures due to the small clusters. We observe deviations from strict superparamagnetic behavior due to non-negligible local anisotropy effects at low temperatures and low fields. The Kondo effect is particulary enhanced in the Cu-Fe films which have higher concentration of isolated Fe atoms and small sizes clusters. The magnetoresistivity Delta rho / rho of our films is dominated (for 0 < = mu sub 0 H < =15T) by a linear term in H, attributed to GMR-like effect from spin-dependent scattering when an electron passes between adjacent large and small clusters. At low fields we observe instead Delta / rho proportional to H exp 2 , due to the usual GMR effect between large clusters, during the alignment of their easy axes. The relevant physical differences (structural, magnetic and magnetoresistive) observed in our ion-implanted diluted Fe films, with respect to the concentrated granular films are critically analysed.