Electronic structure near Fermi level of Pr 2 CoFeO 6 (at 300 K) was investigated by X-ray photoemission spectroscopy (XPS) technique. All three cations, i.e., Pr, Co and Fe were found to be trivalent in nature. XPS analysis also suggested the system to be insulating in nature. Moreover, Raman spectroscopy study indicated the random distribution of the B-site ions (Co/Fe) triggered by same charge states. In temperature-dependent Raman study, the relative heights of the two observed phonon modes exhibited anomalous behaviour near magnetic transition temperature T N~2 70 K, thus indicating towards interplay between spin and phonon in the system. Furthermore, clear anomalous softening was observed below T N which confirmed the existence of strong spin-phonon coupling occurring for at least two phonon modes of the system. The line width analysis of the phonon modes essentially ruled out the role of magnetostriction effect in the observed phonon anomaly. The investigation of the lattice parameter variation across T N (obtained from the temperature-dependent neutron diffraction measurements) further confirmed the existence of the spin-phonon coupling.

The magnetic spin ordering and the magnetization dynamics of a double perovskite Pr2CoFeO6 have been investigated by employing the (dc and ac) magnetization and neutron powder diffraction techniques. The study revealed that Pr2CoFeO6 adopted a B-site disordered orthorhombic structure (Pnma). Furthermore, ab initio band structure calculations suggested an insulating antiferromagnetic ground state. Magnetization measurements revealed that the system possesses a spectrum of competing magnetic phases, viz., long range canted antiferromagnetic (AFM) spin ordering (TN ∼ 269 K), Griffiths-like phase, re-entrant cluster glass (TG ∼ 34 K), and exchange bias effects. The neutron diffraction study divulged the exhibition of a long range G-type of canted AFM spin ordering. The random nonmagnetic dilution of magnetic Fe3+ (high spin) ions by Co3+ (low spin) ions due to B-site disorder essentially played a crucial role in manifesting such magnetic properties of the system.

Electronic structure, electrical transport, dc and ac magnetization properties of the hole substituted (Sr 2+ ) partially B-site disordered double perovskite Pr 2-x Sr x CoMnO 6 system have been investigated.Electronic structure was probed by employing X-ray photoemission spectroscopy (XPS) measurements. The study suggested the presence of mixed valence states of the B-site ions (Co 2+ /Co 3+ and Mn 3+ /Mn 4+ ) with significant enhancement of the average oxidation states due to hole doping. The mere absence of electronic states near the Fermi level in the valence band (VB) spectra for both of the pure (x=0.0) and Sr doped (x=0.5) systems indicated the insulating nature of the samples. Sr substitution is observed to increase the spectral weight near the Fermi level suggesting for an enhanced conductivity of the hole doped system. The temperature variation of electrical resistivity measurements revealed the insulating nature for both the systems, thus supporting the VB spectra results. The resistivity curves were observed to follow the variable range hopping (VRH) mechanism in the entire temperature range while the analysis showed a significance enhancement in the carrier concentration due to the hole doping. The dc magnetization data divulged a Griffiths like phase above the long range ordering temperature. A typical re-entrant spin glass like phase driven by the inherent anti-site disorder (ASD) has been maidenly recognized by ac susceptibility study for both the pure and doped systems. Most interestingly, the emergence of a new cluster glass like phase (immediately below the magnetic ordering temperature and above the spin-glass transition temperature) solely driven by the Sr substitution has been unravelled by ac magnetization dynamics study. Observation of these dual glassy states in a single system is scarce and hence placed the present system amongst the rare materials. The isothermal magnetization measurements further probed the exhibition of the giant exchange bias effect emanated from the existence of multiple magnetic phases.

An ambient atmosphere single quantum dot (QDs) rectifying diode with tunable threshold voltage has been fabricated using cobalt (Co) doped CdS QDs with a device structure of ITO/ZnO/QDs.

The magneto-transport properties of Bi2Se3–ySy were investigated. Magnetoresistance (MR) decreases with an increase in the S content, and finally, for 7% (i.e., y = 0.21) S doping, the magnetoresistance becomes negative. This negative MR is unusual as it is observed when a magnetic field is applied in the perpendicular direction to the plane of the sample. The magneto-transport behavior shows the Shubnikov–de Haas (SdH) oscillation, indicating the coexistence of surface and bulk states. The negative MR has been attributed to the non-trivial bulk conduction.

La based Co-Fe combined double perovskite (La 1.8 Pr 0.2 CoFeO 6 ) was synthesized and the dielectric (zero-field and in-field), magnetic, x-ray absorption and Raman spectroscopy measurements have been investigated for La 1.8 Pr 0.2 CoFeO 6 double perovskite. The existence of re-entrant cluster glass state is observed. The magneto-dielectric (MD) is found in two temperature regions (25-80 K and 125-275 K). It has been demonstrated that the observed MD at low and high temperatures are respectively due to the spin freezing and the spin-lattice coupling. Furthermore, the very large dielectric constant and the low loss suggest that La 1.8 Pr 0.2 CoFeO 6 is very important from the application point of view.

The structural, magnetic and Raman effect have been investigated on (Tb 1-x Eu x ) 2 Ti 2 O 7 .From structural study it is clear that Eu substitutes the Tb in Tb 2 Ti 2 O 7 . Raman effect study indicates the existence of hardening due to phonon-phonon anharmonic interaction. From dcmagnetic measurement it is observed that in Eu rich samples contribution of dipolar interaction is significant. From ac magnetic measurement of (Tb 1-x Eu x ) 2 Ti 2 O 7 a new single ion weak spin freezing ~ 33K at zero magnetic field is observed. On applying a field of 1T, all the compounds show a field induced transition (T * ) which shifts towards higher temperature with increase of Eu content. This field induced transition corresponds to single moment saturation.

Structural, pressure-dependent resistivity, angle resolved photoemission spectroscopy (ARPES), x-ray photoelectron diffraction (XPD) and band structure by DFT calculation have been investigated for BiSbTe3 Topological insulator. It has been demonstrated that the Dirac point of the topological surface state (TSS) located exactly at the Fermi level. Additionally, superconductivity emerges under pressure of 8 GPa with a critical temperature of ∼2.5 K. With further increase of pressure, the superconducting transition temperature (Tc) increases and at 14 GPa it shows the maximum Tc (∼3.3 K). It has also been shown that the surface state remains unchanged under pressure and has been suggested that the origin of the superconductivity is due to the bulk state. The investigation indicates that the BiSbTe3 has robust surface states and becomes superconductor under pressure.