Anomalous Transport Phenomena of Photoelectrons in the Ferromagnetic Semiconductor EuO

抄録

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 cm²/V. sec at H=0 to 160 cm²/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.