Magnetic state of Tm ions in the Tm xSm 1− xS system

Abstract

The magnetic susceptibility χ of Tm x Sm 1− x S system was measured in the range 7.5–300 K. Our analysis of χ(T) shows that Tm ions have the valency +3 in the whole concentration range 0 < x < 1. Moreover, the magnetic field behavior strongly depends on the interaction between Tm +3 and electrons. In the range 0 < x < 0.16 where Tm +3 forms a donor center, the interaction of Tm +3 with a bound electron at temperatures T < 80 K is ferromagnetic, therefore the total moment of the donor center is equal to 6.5. At T > 150 K the interaction becomes antiferromagnetic which leads to the total moment 5.5. At low temperatures and concentrations 0.16 < x < 0.25 the interaction of Tm +3 with electrons remains ferromagnetic which gives evidence for strong electron localization within an impurity band. In the concentration range 0.25 < x < 1 magnetic behavior of Tm +3 is almost temperature independent and corresponds to the behavior of free Tm +3 ions with the moment 6.