MAGNETIC STATE OF TM IONS IN THE TMXSM1-XS SYSTEM

The magnetic susceptibility (chi) of TmxSm1-xS system was measured in the range 7.5-300 K. Our analysis of (chi)(T) shows that Tm ions have the valency +3 in the whole concentration range 0 < x < 1. Moreover, t he 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 dono r center, the interaction of Tm+3 with a bound electron at temperature s T < 80K is ferromagnetic, therefore the total moment of the donor ce nter is equal to 6.5. At T > 150 K the interaction becomes antiferroma gnetic which leads to the total moment 5.5. At low temperatures and co ncentrations 0.16 < x < 0.25 the interaction of Tm+3 with electrons re mains ferromagnetic which gives evidence for strong electron localizat ion within an impurity band. In the concentration range 0.25 < x < 1 m agnetic behavior of Tm+3 is almost temperature independent and corresp onds to the behavior of free Tm+3 ions with the moment 6.