The Electrical Transport Properties Of Ni-SiO₂Granular Films And Ni Thin Films

We fabricated a series of Ni-SiO2granular films with different metal volume fraction x (0.48≤x≤1.00) on glass substrates by cosputtering method and a series of Ni films with different thicknesses (2.5-100nm) by rf sputtering deposition method. We investigated the microstructure, magnetic property, the correction of quantum effect to longitudinal conductivity, anomalous Hall resistivity and conductivity, the relation between anomalous Hall resistivity ρxys and longitudinal resistivity ρxx in these films.The Ni-SiO2films present excellent granular structure from the TEM analysis. For the study of longitudinal resistivity:when x>0.50, these samples show a metal conductive behavior; when x≤0.50, these samples show a semiconductor conductive behavior. The percolation threshold is x-0.50by analyzing the temperature coefficient of resistivity. We observed giant Hall effect in Ni-SiO2granular films, the anomalous Hall coefficient and ordinary Hall coefficient both increased more than two orders of magnitude when the metal volume fraction reduced to the percolation threshold. And we studied the scaling relation of anomalous Hall effect:the relation between ρxys and ρxx is investigated in each films (the implicit variable is temperature), the scaling of anoamous Hall effect for x≥0.70obeys ρxy∝ρxx, which indicates skew scatting dominates; however, there is no scaling between pxy and ρxx for x<0.70, which can be interpreted by the thoey of anomalous Hall effect in granular films. In addition, the relation between ρxys normalized by carrier concentration and ρxx was studied (the implicit variable is the metal volume fraction), the scaling relation obeys ρxys/n∝ρxx2for the films with0.52≤x≤0.78, which implys that the anomalous Hall current is dissipationless and the anomalous Hall effect in Ni-SiO2granular films originates from intrinsic mechanism.For the Ni films with the thickness varying from2.5nm to16nm, the ρxx increased with decreasing temperature at low temperature, which is due to electron-electron interaction or weak localization. By our analysis, we found the logarithmic temperature dependence of ρxx, ρxys and anomalous Hall conductivity for the films of3-16nm, which is due to weak localization. Moreover, we obtained the unconventional scaling relations between the anomalous Hall conductivity and longitudinal conductivity σxy∝σxxγ, γ≥1.79at the low conductivity regime, which has some deviation with the predicted1.6(σxy∝σxx1.6) by the unified scaling theory. We know that weak localization only exists at low temperature, however, this unconventional scaling relation also presents at high temperature (100K、200K), which indicates that this deviation may not be induced by the electron localization. And the origin of this unconventional scaling still needs to be further investigated...