Uranium diluted in IV-VI compounds

We have studied the magnetic properties of a new D.M.S namely Pb1-xUxTe. The uranium is an interesting magnetic ion, because the shell responsible of the localised magnetic moments, is the 5f shell; its orbit is more delocalized with respect to the 4f shell of the usual rare earth included in SMSC like Gd3+ or Eu2+. Magnetization and magnetic susceptibility measurements have been performed. Low temperature magnetization shows that for x >1.4% there exists a ferromagnetic component, this result is supported by the high temperature susceptibility which presents a Curie temperature of 97 K. This value of Tc is a signature of the existence of UTe clusters, which has the same Tc. Around Tc the magnetization shows a slope change. The low temperature magnetization, enables us to deduce, in addition to the ferromagnetic component, the contribution of the singles magnetic ions and of the pairs. The Jp which is the exchange interaction in the pair, is weakly antiferromagnetic, and could be explained by a superexchange process via the Te anion.