  Universality of the extraordinary Hall effect scaling was tested in granular
three-dimensional Ni-SiO2 films across the metal-insulator transition. Three
types of magnetotransport behavior have been identified: metallic, weakly
insulating and strongly insulating. Scaling between both the ordinary and
extraordinary Hall effects and material resistivity is absent in the weakly
insulating range characterized by logarithmic temperature dependence of
conductivity. The results provide compelling experimental confirmation to
recent models of granular metals predicting transition from logarithmic to
exponential conductivity temperature dependence when inter-granular conductance
drops below the quantum conductance value and loss of Hall effect scaling when
inter-granular conductance is higher than the quantum one. The effect was found
at high temperatures and reflects the granular structure of material rather
than low temperature quantum corrections.
