Unusual paramagnetic centers in PbTe undoped crystals

We present the results of the first experimental observation of unusual paramagnetism in solid when magnetic susceptibility of paramagnetic centers doesn't depend on temperature but drastically decreases when the applied magnetic field increases. This unusual combination of the field and temperature dependences of magnetic susceptibility was observed in the studies of magnetization and magnetic susceptibility performed in the wide range of temperatures (1.7–300 K) and magnetic fields (0–5.0 T) on the bulk and surface PbTe powder samples manufactured from crystal ingots grown by Bridgman method out of high-purity Pb and Te. We believe that presence of these features indicate that we are dealing with unknown untypical paramagnetism of paramagnetic centers in solid. We observed that the concentration of such unusual paramagnetic centers in PbTe crystal ingots increases towards their surface. Increase of the concentration of the centers can be so strong that it causes a transition of PbTe from the diamagnetic state to the paramagnetic one in quite wide range of low magnetic fields. Possible nature of the observed unusual paramagnetic centers is discussed.