The S exchange interaction in Gd doped La3-x□xS4

In this letter we show that the ESR line widths of Gd³⁺ in La₂S₃ (an insulator) and La₃S₄ (a metal) are the same at 0° K, but that in the latter it has a linear temperature dependence. Because of the identical crystal structures of these compounds this result can unequivically be interpreted as arising from an exchange interaction between the localized moment and the conduction electrons. The system La_3-x□_xS₄ therefore is an excellent host for studying the effects of localized moment-conduction electron interactions.