Transport Properties of the High Temperature Phase of Fe3O4.

Electrical conductivity and Hall effect were measured for the high temperature phase of Fe 3 O 4 single crystals with different stoichiometry, in an external magnetic field up to 27 kOe. It was confirmed that the transport properties do not depend so much on stoichiometry, in contrast to the low temperature phase. Temperature dependence of the conductivity and magnetoresistance as well as extraordinary Hall coefficient which changes sign at 650 K indicate that not only 3 d electrons of Fe ions in the B site but also of those in the A site and/or 2 p electrons of O ions contribute to the transport above 400 K. Below 250 K, extraordinary Hall coefficient is proportional to ρ 0.5 . The results of the present experiments are discussed in connection with previous reports. Formation of large polarons below 250 K is suggested.