We studied both the resistivity and the Hall resistivity of cosputtered granular Ni–SiO2 films with the metal volume fraction x in the range of 0.5–1.0. Near the metal-insulator transition, or x of about 0.53–0.61, the saturated value of the Hall resistivity was up to 2×10−4 Ω cm. This value is almost 4 orders of magnitude greater than that of pure nickel. Both the resistivity and the Hall resistivity varied weakly with temperature, throughout the range of 5–300 K. We suggest that the percolating ferromagnetic granular metal films can be an alternative candidate material for high sensitivity Hall sensors.

We have studied the resistivity, magnetoresistivity, and Hall resistivity for a few Fex(SiO2)1−x granular films with Fe volume fraction x near the metal insulator transition threshold xc. Both the ordinary Hall coefficient R0 and the saturated extraordinary Hall resistivity ρxys were found to be enhanced by a factor of 104 when x approaches xc. The largest measurable R0 and ρxys at room temperature are about 10−3 μΩ cm/G and 250 μΩ cm, respectively. By comparing with the Ni-rich NiFe–SiO2 system [A. B. Pakhomov, X. Yan, and B. Zhao, Appl. Phys. Lett. 67, 3497 (1995)], we found that the correlation between giant Hall effect and the resistivity with a −log T-like dependence is independent of the sign of the carrier. The feasibility of using such a system as a magnetic-field sensor is discussed.

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