Insulator-Metal Transition in Sm_<1-x>Gd_xS Induced by Temperature and Pressure

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The effects of Gd substitution and pressure were investigated on the temperature dependence of electrical resistivity and magnetic susceptibility of the compounds Sm^<1-x>Gd_xS. The compounds with 0.15<x<0.25 exhibit a first-order phase transition from metallic to semiconducting when they are cooled at atmospheric pressure. In the range of 0.30<x<0.7, the resistivity decreases with decreasing temperature and shows a minimum. In the range of x>0.8, the temperature dependence of resistivity shows the characteristics of antiferromagnetic metal. The Neel point decreases with decreasing Gd concentration. The resistance of SmS was measured under pressure up to 140 kbar at room temperature and an abrupt pressure-induced decrease of resistance was observed at 6.5 kbar, but no significant change of resistance except for that at 6.5 kbar was detected. For the compounds with 0<px<0.15, it was found that there occur pressure-induced two transitions at pressures P_<c1> and P_<c2> at which abrupt decrease in resistivity were subsequently observed.
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