The role of grain boundaries in determining the transport properties of magnetite

We present magnetoresistance and Hall-effect measurements on single-crystal magnetite ( Fe 3 O 4 ) close to the Verwey transition T V = 123.8 K . We show that the formation of grain boundaries accompanying the reduction in crystal symmetry plays a significant role in the electron-scattering mechanism, and that grain boundaries can account for the apparent change in sign of the charge carriers below T V .