Hall effect of itinerant electron metamagnet Co(S1-Se )2

We have studied the Hall effect of Co(S _{1- x}Se _x) ₂ with 0.08 ≤ x ≤ 0.14, which shows itinerant electron metamagnetism (IEM). The Hall resistivity ρ _xy was measured as a function of the magnetic field B at various temperatures. It is found that ρ _xy decreases nearly linearly with increasing B in the paramagnetic state, while it has a positive slope in the ferromagnetic state. Abrupt drops were observed at around the metamagnetic transition field in the ρ _xy – B curves, which are attributable to the anomalous Hall effect. From the analyses of the ρ _xy – B curves and the magnetization curves, we estimated the anomalous Hall coefficient, the normal (ordinary) Hall coefficient in the ferromagnetic state, and that in the paramagnetic state. Appearance of both ferromagnetic and paramagnetic states depending on a magnetic field in IEM makes it possible to estimate these values, simultaneously. The estimated normal Hall coefficients are compared with the theoretical values calculated from the energy band structures. The present study has demonstrated that IEM provides a suitable stage to understand the electronic structures of both ferromagnetic and paramagnetic states of the itinerant electron system at the same temperature.