Giant Hall effect in granular Fe–SiO2 film

We have studied the resistivity, magnetoresistivity, and Hall resistivity for a few ${\mathrm{Fe}}_x({\mathrm{SiO}}_2{)}_{\text{1−x}}$ granular films with Fe volume fraction $x$ near the metal insulator transition threshold $x_c.$ Both the ordinary Hall coefficient $R_0$ and the saturated extraordinary Hall resistivity ${\rho }_{\mathrm{xys}}$ were found to be enhanced by a factor of ${10}^4$ when $x$ approaches $x_c.$ The largest measurable $R_0$ and ${\rho }_{\mathrm{xys}}$ at room temperature are about ${10}^{\text{−3}}$ μΩ cm/G and 250 μΩ cm, respectively. By comparing with the Ni-rich ${\mathrm{NiFe–SiO}}_2$ 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 $-\log \mathrm{\hspace{0.17em}T}$ -like dependence is independent of the sign of the carrier. The feasibility of using such a system as a magnetic-field sensor is discussed.