Sangeeta Thakur

Improvement in electric and dielectric properties of nanoferrite synthesized via reverse micelle technique

Nano nickel zinc ferrite (Ni0.58Zn0.42Fe2O4) with fascinating dielectric properties which reveal a direction for application was synthesized by reverse micelle technique. Dielectric constant and dielectric losses are controlled up to a measurement temperature of around 473K at higher frequency range of 9–19MHz. The dielectric loss of the sample investigated at room temperature is only 0.003 at 19MHz. The presently studied nanoferrite also exhibits a high value of dc resistivity, 108Ωcm. High resistivity and low dielectric constant and loss can be corelated to small grain size and better compositional stoichiometry obtained as a result of processing via reverse micelle technique at low sintering temperature (773K).

Room temperature ferromagnetic ordering in indium substituted nano-nickel-zinc ferrite

Nano-nickel-zinc-indium ferrite (NZIFO)(Ni0.58Zn0.42InxFe2−xO4) with varied quantities of indium (x=0,0.1,0.2) have been synthesized via reverse micelle technique. X-ray diffraction and transmission electron microscopy confirmed the size, structure, and morphology of the nanoferrites. The addition of indium in nickel-zinc ferrite (NZFO) has been shown to play a crucial role in enhancing the magnetic properties. Room temperature Mossbauer spectra revealed that the nano-NZFO ferrite exhibit collective magnetic excitations, while indium doped NZFO samples have the ferromagnetic phase. The dependence of Mossbauer parameters, viz. isomer shift, quadrupole splitting, linewidth, and hyperfine magnetic field, on In3+ concentration has been studied. Mossbauer study on these nanosystems shows that the cation distribution not only depends on the particle size but also on the preparation route. Mossbauer results are also supported by magnetization data. Well defined sextets and appearance of hysteresis at room temper...

Complex spectral evolution in a BCS superconductor, ZrB12

We investigate the electronic structure of a complex conventional superconductor, ZrB12 employing high resolution photoemission spectroscopy and ab initio band structure calculations. The experimental valence band spectra could be described reasonably well within the local density approximation. Energy bands close to the Fermi level possess t2g symmetry and the Fermi level is found to be in the proximity of quantum fluctuation regime. The spectral lineshape in the high resolution spectra is complex exhibiting signature of a deviation from Fermi liquid behavior. A dip at the Fermi level emerges above the superconducting transition temperature that gradually grows with the decrease in temperature. The spectral simulation of the dip and spectral lineshape based on a phenomenological self energy suggests finite electron pair lifetime and a pseudogap above the superconducting transition temperature.

Surface bulk differences in a conventional superconductor, ZrB12

We studied the electronic structure of a conventional superconductor, ZrB(12) using high resolution x-photoemission spectroscopy and single crystalline samples. Experimental results with different bulk sensitivity reveals boron deficiency and different valence states of Zr at the surface relative to the bulk. Signature of a satellite features is observed in the Zr core level spectra corresponding to the bulk of the material suggesting importance of electron correlation among the conduction electrons in the bulk while the surface appears to be uncorrelated. These results provide an insight in fabricating devices based on such superconductors.

Exceptional surface and bulk electronic structures in a topological insulator, Bi2Se3

The outstanding problem in topological insulators is the bulk metallicity underneath topologically ordered surface states and the appearance of Dirac point far away from the Fermi energy. Enormous efforts are being devoted to get the Dirac point at the Fermi level via exposure to foreign materials so that these materials can be used in technology and realize novel fundamental physics. Ironically, the conclusion of bulk metallicity in the electronic structure is essentially based on the angle resolved photoemission spectroscopy, a highly surface sensitive technique. Here, we employed state-of-the-art hard x-ray photoemission spectroscopy with judiciously chosen experiment geometry to delineate the bulk electronic structure of a topological insulator and a potential thermoelectric material, Bi2Se3. The results exhibit signature of insulating bulk electronic structure with tiny intensities at akin to defect/vacancy induced doped states in the semiconductors. The core level spectra exhibit intense plasmon peak associated to core level excitations manifesting the signature of coupling of electrons to the collective excitations, a possible case of plasmon-phonon coupling. In addition, a new loss feature appear in the core level spectra indicating presence of additional collective excitations in the system.

Evidence of bulk nature of the Kondo effect and different surface potentials in CeB6

We have investigated the electronic structure of CeB6 using photoemission spectroscopy as a function of surface sensitivity of the technique. Experimental results provide evidence that Kondo effect is a bulk phenomenon. The Madelung potential at the surface is found to be different from that of the bulk.

Magnetic ordering in nickel-zinc nanoferrite thin film formed by Langmuir Blodgett technique

Nickel-zinc nanoferrite thin films, which reveal application for magnetic materials, were prepared by Langmuir-Blodgett technique. X-ray reflectivity fitting was done using three layer model. Thickness of a monolayer of nanoparticles is obtained as 23.5 A. Surface roughness increases as the thickness of the film increases. Fourier transform infrared spectra confirmed that the structure remains cubic spinel after thin film formation. We have measured zero-field cooled and field cooled magnetization and discussed the behavior in three parts: the ferromagnetic part, transition region, and the superparamagnetic part.

Processing and Characterization of Cobalt‐Zinc Nano Ferrite

Co(1−x)ZnxFe2O4 (x = 0.1, 0.2, 0.3, 0.4) nano magnetic systems were prepared by solution combustion method. The powder samples are characterized by x‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and Mossbauer spectroscopy. The average crystallite sizes of the prepared sample obtained from XRD are well consistent with particle size obtained from TEM images. Fourier transform confirm the spinel phase structure of cobalt zinc ferrite. Mossbauer spectra indicate that sample with 40% zinc concentration exhibits the collective magnetic excitations.

Characterization of magnetic nano materials by Mössbauer spectroscopy

The use of a non-destructive nuclear-physical method, namely 57Fe Mossbauer spectroscopy, is discussed for the investigation of magnetic and structural arrangement of Fe-based nano-crystalline nickel-zinc-indium ferrites (NZIFO). Nano NZIFO particles (Ni0.58Zn0.42InxFe2−xO4) with varied quantities of indium (x = 0, 0.1, 0.2) have been chemically synthesized through a reverse micelle reaction and investigated by X-ray diffraction, transmission electron microscopy and by magnetic and Mossbauer spectral studies. Here a comparison between low-temperature and room temperature Mossbauer spectra is presented. Well defined sextets at 5 K provide information about the structure and magnetic states of atoms located in different structural positions. The dependence of Mossbauer parameters, viz, isomer shift, quadrupole splitting, linewidth and hyperfine magnetic field on In3+ concentration have been discussed. Detailed Mossbauer results, as well as the interest of these materials both for applied science perspectives are presented. Mossbauer results are also supported by magnetization data. With these interesting ferromagnetic properties Indium substituted nano nickel-zinc ferrites have potential applications in magnetic storage data.

Electronic structure of a superconducting boride, ZrB12

We investigate the electronic structure of a boride superconductor, ZrB12 employing high resolution photoemission spectroscopy and ab initio band structure calculations. Sharp B 1s and Zr 3d core level spectra with distinct signature of the satellites exhibits good quality of the sample. The band structure results indicate dominant contribution from the B 2p electronic states in the valence band. However, the experimental spectra indicate large contribution from the Zr 4d states near Fermi level suggesting their important role in the superconductivity.