Magnetism and Magnetocaloric Effect in TlCo2−x Ni X S2 (0 $\leqslant$ X $\leqslant$ 0.05)

We have investigated the magnetism and magnetocaloric effect of TlCo2-x Ni x S2 (0 [Formula: see text] x [Formula: see text] 0.05). TlCo2S2 and TlCo1.97Ni0.03S2 are ferromagnetically ordered below 153 K and 142 K with saturated moment 0.82 [Formula: see text] [Formula: see text]/Co and 0.80 [Formula: see text] [Formula: see text]/Co, respectively, while TlCo1.95Ni0.05S2 shows ferromagnetic transition at 132 K. The magnetism displays slightly itinerant character, as inferred from the Rhodes-Wohlfarth ratio. An unusual historical dependence of magnetization in TlCo1.95Ni0.05S2 is consistently observed by scanning both the temperature and magnetic field. The isothermal magnetic entropy change ([Formula: see text] S [Formula: see text]) of TlCo2S2 and TlCo1.95Ni0.05S2 are calculated by Maxwell relation and a temperature averaged entropy change is adopted to estimate the figure of merit for the compounds.