Resistivity and Hall effect of EuSe in fields up to 150 kOe

The resistivity ρ(Hₑₓₜ,T) and Hall effect were studied in ten n-type EuSe single-crystal samples with room-temperature carrier concentrations from 4.2 ×{} 10¹⁸ to 3.5 ×{} 10¹⁹ electrons/cm³. The electrical measurements were performed at temperatures 1.6≤T≤300 K and external magnetic fields 0≤Hₑₓₜ≤150 kOe, and were supplemented by magnetization and differential susceptibility measurements to aid in the interpretation. The following phenomena were observed: (a) A very large peak in the zero-field resistivity occurred at a temperature Tₘₐₓ which varied from {~} 7 to {~} 13 K, depending on the sample. (b) A negative magnetoresistance was observed for most temperatures and was very large near Tₘₐₓ. (c) However, in a limited temperature interval well above Tₘₐₓ, a positive magnetoresistance was observed at low fields (followed by a negative magnetoresistance at higher fields). (d) Below {~} 3 K, the zero-field resistivity increased rapidly with decreasing T, except for the sample with the highest carrier concentration. (e) The anomalous Hall effect was negligible at temperatures T≤4.2 K. Much of the data are interpreted in terms of band conduction. The mobility is then limited by spin-disorder scattering and it increases with increasing Hₑₓₜ, resulting in a negative magnetoresistance. This description fails when both TTₘₐₓ and Hₑₓₜ<1 to 10 kOe. Under these conditions, the very high resistivity is attributed to the localization (trapping) of electrons by the s-f (or d-f) interaction. At temperatures for which the electrons are localized at Hₑₓₜ=0, a field of 1 to 10 kOe delocalizes the electrons and, therefore, leads to band conduction and a much lower resistivity. At higher fields there is a negative magnetoresistance (smaller than at low fields) due to the reduction in spin-disorder scattering of the band electrons. A model for the positive magnetoresistance, which focuses on the spin splitting of the conduction band by a magnetic field, is presented in the following paper.