Anomalous Transport Phenomena of Photoelectrons in the Ferromagnetic Semiconductor EuO

Anomalous transport phenomena of photoelectrons in pure EuO crystals have been studied over the temperature range from T =4.2 K to 80 K and in the magnetic fields up to H =50 kOe by using a fast-pulse technique with blocking electrodes. The Redfield geometry was used to determine directly the value of Hall mobility of photocarriers, µ H . Anomalous behaviours of photoconductivity such as an abrupt increase below the Curie temperature T c =69.5 K and a large negative-magnetoresistance effect around T c were observed. The value of µ H has been measured as a function of both the temperature and the magnetic field. It was directly found that the value of µ H varies with H around T c ; the µ H -value at T =63.5 K increases from 90 cm 2 /V. sec at H =0 to 160 cm 2 /V. sec at H =15 kOe. Thus, the anomalous transport phenomema in pure EuO crystals around T c have been experimentally confirmed, for the first time, to be mainly due to the mobility change. Experimental results are discussed in terms of the transport theory based on the wide band scheme and the spin disorder scattering due to the s - f exchange interaction.