Universal scaling of the anomalous Hall effect in Fe3 O4 epitaxial thin films

We report a systematic study of the anomalous Hall effect in epitaxial thin films of magnetite grown on MgO (001) substrates as a function of film thickness (from 5 to 150 nm) and temperature (60K < T < 300K). The Hall resistivity was found to be negative for all the measured temperature range, presenting a huge enhancement at temperatures below the Verwey transition, reaching values above 1mΩ cm. The anomalous Hall conductivity scales as σH ∝ σ 1.6/xx over four decades of the longitudinal conductivity σxx in all the samples, in agreement with a recent unified theory for the anomalous Hall effect