Anomalous magnetic behaviour of Bi based tetradymites

Abstract

This work investigates the magnetic properties of the Bi-based bulk Bi2(Se1−xTex)3 tetradymites. The samples were prepared using the melting technique, and all composites are crystallised in the R3m Rhombohedral structure. The lattice cell volume increases monotonically with the Te introduction due to the larger size of Te in comparison with Se. The electrical resistivity data show a metal–semiconductor transition at a certain temperature (Tm) that arises from the overlapping between the 6p and 6s bands. The metal-like behaviour below Tm is in correspondence with the semiconducting degeneracy state, and the empirical analysis has confirmed the metal characteristic scattering mechanisms. The resistivity of the pristine Bi2Se3 compound decreases with the low Te doping level, then increases monotonically with the further Te amounts. This behaviour can be attributed to grain size effect and the change in carriers concentration and mobility. The magnetic measurements have shown the non-pure diamagnetism for the Bi2(Se1−xTex)3 composites, in disagreement with several studies, and show the coexistence of a paramagnetic component. This paramagnetic component arises from the orbital magnetisation, where, the electrons abundance (due to Te and the electron source defects) bends the electronic band, forming 2-dimensional electron gas state that leads to the spin-orbital magnetisation (the source of orbital magnetisation).