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Metal-insulator transition upon heating and negative-differential-resistive-switching induced by self-heating in BaCo0.9Ni0.1S1.8

The layered compound BaCo1-xNixS2-y (0.05<x<0.2 and 0.05<y<0.2) exhibits an unusual first-order structural and electronic phase transition from a low-T monoclinic paramagnetic metal to a high-T tetragonal antiferromagnetic insulator around 200 K with huge hysteresis (~ 40 K) and large volume change (~0.01). Here we report on unusual voltage-controlled resistive switching followed by current-controlled resistive switching induced by self-heating in polycrystalline BaCo1-xNixS2-y (nominal x=0.1 and y=0.2). These were due to the steep metal to insulator transition upon heating followed by the activated behavior of the resistivity above the transition. The major role of Joule heating in switching is supported by the absence of nonlinearity in the current as function of voltage, I(V), obtained in pulsed measurements, in the range of electric fields relevant to d.c. measurements. The voltage-controlled negative differential resistance around the threshold for switching was explained by a simple model of self-heating. The main difficulty in modeling I(V) from the samples resistance as function of temperature R(T) was the progressive increase of R(T), and to a lesser extend the decrease of the resistance jumps at the transitions, caused by the damage induced by cycling through the transitions by heating or self-heating. This was dealt with by following systematically R(T) over many cycles and by using the data of R(T) in the heating cycle closest to that of the self-heating one.