Ferromagnetism in diluted Pb1-x-yGexCryTe magnetic semiconductors

Magnetic properties of Pb1-x-yGexCry Te alloys (x = 0.02-0.20, y = 0.01-0.08) were studied. It was detected that the magnetic susceptibility of alloys consists of two contributions: the paramagnetic Curie-Weiss part (the temperature region is T < 50 K) caused, probably, by the Cr3+ ion paramagnetism, and the high-temperature ferromagnetic part (T < 300 K). The dependences of the concentration of magnetic centers on the composition of the matrix were obtained from the paramagnetic and ferromagnetic contributions. It was shown that a decrease in the concentration of paramagnetic centers can be, at least qualitatively, explained by the transformation of the electronic structure as the germanium concentration increases. A phenomenological model was suggested, which explains the behavior of magnetic properties as the chromium content increases, and possible mechanisms of ferromagnetic ordering in studied alloys are discussed.