On the origin of the giant Hall effect in magnetic granular metals

A large, by a factor of similar to 10(3)-10(4), enhancement of Hall effect in cosputtered magnetic granular metals such as (NiFe)(x)-(SiO2)(1-x) near the metal-insulator transition has been termed giant Hall effect (GHE). It is associated with a high resistivity which increases slowly with decreasing temperature. We suggest that particle-size distribution which is singular at zero and quantum size effects may be responsible for these phenomena. From our scaling analysis of the relations between resistivity, and the ordinary and extraordinary Hall effects, it follows that the extraordinary Hall resistivity rho(xys) scales with mobility as-rho(xys)proportional to mu(-gamma) with the exponent gamma approximate to 0.5, which is characteristically different from the predictions of both the skew scattering (gamma approximate to 1) and the side jump (gamma approximate to 2) theories in homogeneous ferromagnets.