Magnetic Constitution of Topologically Trivial Thermoelectric PbTe:Cr

Abstract

In this paper we report on detailed temperature and magnetic field dependence of magnetization of IV-VI semiconductor PbTe doped with mixed valence transition metal Cr 2+/3+ . The material is studied solely by an integral superconducting quantum interference device magnetometer in order to quantitatively determine the contribution of single substitutional Cr 3+ as well as of various Cr-Te magnetic nanocrystals, including their identification. The applied experimental procedure reveals the presence of about 10 19 cm −3 paramagnetic Cr 3+ ions formed via self-ionization of Cr 2+ resonant donors. These are known to improve the thermoelectric figure of merit parameter zT of this semiconductor. The magnetic finding excellently agrees with previous Hall effect studies thus providing a new experimental support for the proposed electronic structure model of PbTe:Cr system with resonant Cr 2+/3+ state located (at low temperatures) about 100 meV above the bottom of the conduction band. Below room temperature a ferromagnetic-like signal points to the presence of Cr-rich nanocrystalline precipitates. Two most likely candidates, namely: Cr 2 Te 3 and Cr 5 Te 8 are identified upon dedicated temperature cycling of the sample at the remnant state. As an ensemble, the nanocrystals exhibits (blocked) superparamagnetic properties. The magnetic susceptibility of both n-and p-type PbTe in the temperature range 100 < T < 400 K has been established. These magnitudes are essential in proper accounting