Magnetotransport properties of heavy-fermion ferromagnet YbPtGe

The transverse magnetoresistivity ρ_H, Hall coefficient R_H, and specific heat C for H ∥ a below 10kOe for the moderate heavy-fermion ferromagnet YbPtGe with the Curie-temperature T_C = 5.4 K are reported. It is observed that the ρ_H(T) values for the currents along the three crystallographic axes markedly decrease below 30 K with increasing applied magnetic field up to 90kOe. Below T_C, ρ_H(H) at low fields show peak structures for H ∥ a and H ∥ b, and a shoulder for H ∥ c, the positions of which correspond to those of shoulders that observed in the field dependence of the magnetization. The sharp peak of C(T) due to magnetic transition decays and shifts to the low-temperature side with increasing field for H ∥ a up to 3kOe. The H-T phase diagram below T_C is proposed from those measurements. In addition, R_H(T) for I ∥ b and H ∥ c at 10kOe increases from a value close to the expected Hall coefficient for a carrier concentration of 1 hole/f.u. with decreasing temperature from 300 K, and shows a peak at 8 K. By the application of a magnetic field, this peak decays and shifts to higher temperatures. R_H(T, H) for I ∥ b and H ∥ a is similar to that for I ∥ b and H ∥ c. These peaks of R_H(T) are ascribed to the extraordinary Hall effect due to the skew scattering of conduction carriers.