Magnetic properties of Ge1−x−yPbxMnyTe cluster-glass system

We present studies of magnetic properties of Ge1−x−yPbxMnyTe bulk crystals with chemical composition varying in the range of 0.180 < x< 0.311 and 0.019 < y < 0.136. Two transitions, one at temperatures below 20 K and the other between 44 and 105 K, are observed. The transitions are associated with the presence of two magnetic subsystems having different chemical compositions – the host lattice and clusters. The transition at higher temperatures is identified as a transition from a paramagnetic state to a spin-glass-like state. The observed magnetic order is interpreted in terms of the carrier mediated ferromagnetism, assuming an exchange interaction among magnetic ions in both subsystems. The experimental results are analyzed theoretically with good accuracy within the spin-wave-theory-based model of a disordered two-phase ferromagnet with the long-range Ruderman–Kittel–Kasuya–Yosida interaction. The magnetic exchange constant, Jpd, having values from 0.47 eV to 0.80 eV gives spin-glass transition temperature, TSG, values close to the experimental values for the Ge-rich phase. The magnetic order observed for the Pb-rich phase is also due to the carrier mediated magnetic interaction. The experimental transition temperatures are fitted with Jpd value ranging from 0.22 eV to 0.28 eV.