Strong Pressure Effect on the Electrical Resistivity of BaCo_1-xNi_xS₂

Electrical resistivities ρ of BaCo_1-xNi_xS₂, which, has a layered structure exhibits the Mott transition with varying x, have been found to be strongly sensitive to pressure over a very wide temperature region. The paramagnetic insulator state, which exists in the region of x ≲ 0.15 above the Néel temperature T_N, exhibits a transition to a metallic state at a rather small value of applied pressure p. The temperature T_N, at which the resistivity ρ exhibits anomalous increase with decreasing T, rapidly decreases with increasing p and becomes zero at the critical value of p = p_c(x) (≲ 15 kbar for x ≥ 0.05). The paramagnetic state thus obtained exhibits roughly T²-like dependence of the resistivity. The metal-insulator transition of the present system is known to be easily controlled by the external pressure.