High quality single crystals of Bi2Se3 were grown using a modified Bridgman technique, the detailed study were carried out using Raman spectroscopy and characterized by Laue diffraction and high resolution transmission electron microscopy. Polarized
Raman scattering measurements were also carried out, and both the A1g and A2g phonon modes showed strong polarization effect, which is consistent with the theoretical prediction. The temperature dependent study (in the temperature range 83 K to 523 K of Raman active modes were reported and observed to follow a systematic red shift. The frequency of these phonon modes are found to vary linearly with temperature and can be explained by first order temperature co-efficient. The temperature co-efficient for A11g, E2g and A21g modes were estimated to be -1.44*10-2, -1.94*10-2 and -1.95*10-2cm-1/K respectively.
In this work we demonstrate that the polycrystalline ribbons of (Ni48Co6)Mn26Al20 with B2 structure at room temperature show a magnetic behavior with competing magnetic exchange interactions leading to frozen disorders at low temperatures. It is esta
blished that by considering the presence of both antiferromagnetic and ferromagnetic sublattices, we can explain the observed magnetic behavior including the metamagnetic transition observed in these samples. From the Arrott plots, the Neel temperature of (Ni48Co6)Mn26Al20 is deduced to be ~170 K and the broad ferro to para like magnetic phase transition is observed at ~ 200 K. Based on Neel theory, a cluster model is used to explain the presence of ferromagnetic and anti-ferromagnetic clusters in the studied ribbons. Formation of ferromagnetic clusters can be understood in terms of positive exchange interactions among the Mn atoms that are neighboring to Co atoms which are located on the Ni sites.
