Transport properties of EuNi₂Ge₂ under high pressure

Transverse magnetoresistance (MR) and Hall effect have been measured for EuNi₂Ge₂ single crystals under high pressures up to 2.0 GPa. The compound undergoes a valence transition from a nearly trivalent state to a divalent state with increasing temperature above 1.6 GPa. It was found that the transverse MR of EuNi₂Ge₂ is negative at low temperatures in the nearly trivalent state, although the compound is nonmagnetic. The origin of the negative MR is discussed. In the temperature dependence of the Hall resistivity ρ_H, large jumps associated with the valence transition were observed at the valence transition temperature. We also examined the field-induced valence transition by the MR and ρ_H measurements. A marked change in the Hall coefficient was observed at the valence transition field. Our analyses suggest that the ordinary Hall effect plays a dominant role in the changes in ρ_H at the valence transition. (author)