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

A large, by a factor of ≈103−104, 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 xys scales with mobility as- xys ∝ μ−y with the exponent γ ≈ 0.5, which is characteristically different from the predictions of both the skew scattering (γ ≈ 1) and the side jump (γ ≈ 2) theories in homogeneous ferromagnets.