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The Bi2Se3 and Mn doped Bi2Se3 (i.e. Bi1.5Mn0.5Se3, referred as BiMnSe) single crystals were grown using a melt growth method and characterized for their structural, electrical and magnetic properties. These crystals were found to be of single phase having rhombohedral structure with the space group (R3¯m). The magnetoresistance measurements have been carried out in the temperature range 5-50 K, under magnetic fields up to 8 T. The variation of resistivity with temperature shows the Metallic behavior in case of Bi2Se3, and up-turn at low temperatures in the BiMnSe. Metallic behavior was observed up to T > 40 K, whereas below 40K, Kondo effect has been observed. A saturating resistance upturn at low temperatures is observed in the BiMnSe, indicating the presence of Kondo effect due to the existence of localized impurity spins. While the Bi2Se3 is diamagnetic, the BiMnSe is in ferromagnetic state at 5 K. This study opens up a new direction to investigate the physics and device applications of magnetically tunable topological insulators.

In the present work, we carried out a systematic study of structure, UV-Vis Spectra and surface conductivity of pure Bi 2 Te 3 , pure Polyaniline (PANI) and Bi 2 Te 3 (5%)-PANI (95%) composite. Bi 2 Te 3 was synthesized by a method similar to solvothermal method, whereas, pure PANI and Bi 2 Te 3 -PANI composite were synthesized by a chemical oxidative method. The materials were structurally characterized and the electrical properties were investigated in the temperature range from room temperature to 100°C. The electrical conductivity of the Bi 2 Te 3 -PANI composite is found to be higher than that of its pure constituents at all the temperatures. The enhancement in the surface conductivity may be due to the PANI generated ordered molecular arrangement of Bi 2 Te 3 in the Bi 2 Te 3 -PANI composite, as confirmed from powder x-ray diffraction, UV-vis spectral analysis.