Magnetic Specific Heat Study of the Competition between Ferro- and Antiferromagnetic Spin-Spin exchange Interactions in PbSnMnTe

Abstract

Magnetic contribution to the specific heat, magnetic susceptibility and Mall effect are experimentally studied in Pb 1-x-ySnyMnxTe semimagnetic semiconductors with y = 0.72 and x = 0.08 and with different carrier concentrations 10 20 < p < 1021 cm-3 . The ferromagnetism observed in crystals with p > 3 x 10 20 cm -3 breaks down with a decreasing concentration of carriers due to an increasing competition between Ruderman-Kittel-KasuyaYoshida and superexchange interactions.PACS numbers: 75.50.Ppa, 75.50.LkPb1-x-ySnyMnx Τe semimagnetic semiconduction form a model diluted magnetic system with metallic electrical properties. Experimental and theoretical studies of magnetic properties of these crystals revealed a decisive role of concentration of carriers p and an important role of a two-band stucture of the valence band [1][2][3]. The results are summarized in the form of (x, p, T) magnetic phase diagram containing both ferromagnetic (FM) and spin-glass (SG) regions depending on the ratio x/p, where x is the concentration of Mn ions [2,3]. The spin-spin interaction mechanism responsible for these magnetic properties is the Ruderman-Kittel-Kasuya-Yoshida (RKKY) indirect exchange interaction via spin polarization of carriers. The strength of the RKKY interaction decreases with decreasing carrier concentration. In the crystals with p < 10 20 cm-3 the antiferro magnetic superexchange (SE) via anions is expected to dominate the spin-spin interactions as is observed in II-VI semimagnetic semiconductors. In IV-VI semimagnetic semiconduction one can control the concentration of carriers by annealing in an appropriate atmosphere. That offers the possibility to change the strength of the RKKY interaction leaving the SE mechanism practically unchanged. The aim of our work is to use this possibility to experimentally study the evolution of the magnetic properties of PbSnMnTe as a function of the relative contribution of ferro and antiferromagnetic interactions.