arXiv subjects

P. Rani

Publications and source records attributed to P. Rani.

6 recordsLinked to original sources

arXiv2023

Direct evidence of terahertz emission arising from anomalous Hall effect

A detailed understanding of the different mechanisms being responsible for terahertz (THz) emission in ferromagnetic (FM) materials will aid in designing efficient THz emitters. In this report, we present direct evidence of THz emission from single layer Co$_{0.4}$Fe$_{0.4}$B$_{0.2}$ (CoFeB) FM thin films. The dominant mechanism being responsible for the THz emission is the anomalous Hall effect (AHE), which is an effect of a net backflow current in the FM layer created by the spin-polarized current reflected at the interfaces of the FM layer. The THz emission from the AHE-based CoFeB emitter is optimized by varying its thickness, orientation, and pump fluence of the laser beam. Results from electrical transport measurements show that skew scattering of charge carriers is responsible for the THz emission in the CoFeB AHE-based THz emitter.

cond-mat.mtrl-sci↗

arXiv2019

Superconductivity below 2.5K in Nb0.25Bi2Se3 topological insulator single crystal

We report crystal growth and below 2.5K superconductivity of Nb0.25Bi2Se3. These crystals are grown by self flux method. The X-ray diffraction (XRD) pattern of as grown crystal flake shows (00l) plane (c-orientation) growth. The Rietveld refinement of crushed crystal powder XRD (PXRD) pattern confirms the phase purity of the studied sample having R-3m space group of rhombohedral crystalline structure. The Raman spectrum of the studied Nb0.25Bi2Se3 crystal distinctly shows three well defined vibrational modes in terms of A11g, Eg2, A21g at around 72, 129 and 173cm-1, which are slightly shifted in comparison to pure Bi2Se3. Magnetization studies in terms of field cooled (FC) and Zero field cooled (ZFC) magnetic susceptibility measurements show the diamagnetic transition (Tconset) of the compound at around 2.5K and near saturation of the same below around 2.1K. The isothernal magnetization (MH) being taken at 2K, revealed the lower critical field (Hc1) of around 50Oe and the upper critical field (Hc2) of 900Oe. It is clear the studied Nb0.25Bi2Se3 is a bulk superconductor. The superconducting critical parameters thus calculated viz. the coherence length, upper and lower critical fields and superconducting transition temperature for as grown Nb0.25Bi2Se3 single crystal are reported here.

cond-mat.supr-con↗

arXiv2019

Hikami-Larkin-Nagaoka (HLN) Fitting of Magneto Transport of Bi2Se3 Single Crystal in Different Magnetic Field Ranges

We report the detailed study of structural micro-structuraland high magnetic field magneto transport propertiesof Bi2Se3single crystal. Bi2Se3 single crystal is grown through conventional solid-state reaction route via the self-flux method. Rietveld analysis on Powder X-ray Diffraction showed that the studied Bi2Se3 crystal is crystallized in single-phase without any impurity. The surface morphology analyzed through Scanning Electron Microscopy study which shows that as-grown single crystal exhibit layered type structure and the quantitative weight of the atomic constituents (Bi and Se) are found to be closeto the stoichiometric amount in energy-dispersive X-ray spectroscopy analysis. Low temperature (2.5K) magneto-resistance (MR) exhibited a v-type cusp around origin at lower magnetic field, which is the sign of weak anti-localization effect. Further, Bi2Se3 single crystal magneto conductivity data is fitted by well-known HLN equation in different magnetic field range of 2Tesla, 4Tesla and 6Tesla and the resultant found that the conduction mechanism of Bi2Se3 is dominated by WAL state.

cond-mat.mtrl-sci↗

arXiv2019

Ultrafast Spectroscopy of Bi2Se3 Topological Insulator

We investigate the ultrafast transient absorption spectrum of Bi2Se3 topological insulator. Bi2Se3 single crystal is grown through conventional solid-state reaction routevia self-flux method. The structural properties have been studied in terms of high-resolution Powder X-ray Diffraction (PXRD). Detailed Rietveld analysis of PXRD of the crystal showed that sample is crystallized in the rhombohedral crystal structure with a space group of R-3m, and the lattice parameters are a=b=4.14A and c=28.7010A. Scanning Electron Microscopy (SEM) result shows perfectly crystalline structure with layered type morphology which evidenced from surface XRD. Energy Dispersive Spectroscopy (EDS) analysis determined quantitative amounts of the constituent atoms, found to be very close to their stoichiometric ratio. Further the fluence dependent nonlinear behaviour is studied by means of ultrafast transient absorption spectroscopy. The ultrafast spectroscopy also predicts the capability of this single crystal to generate Terahertz (THz) radiations (T-rays).

cond-mat.mtrl-sci↗

arXiv2019

Investigation of fundamental and higher harmonic AC magnetic susceptibility of FeSe0.5Te0.5 Superconductor

We present the complex harmonic magnetic susceptibilities of the FeSeTe polycrystalline superconducting sample. The ac magnetic susceptibility is measured as a function of various external perturbations such as temperature, the AC magnetic field amplitude, frequency, and the magnitude of DC bias field. The in phase and out of phase components of the fundamental and third harmonics of ac susceptibility are found to vary as a function of the AC drive field. The imaginary part of third harmonics shows two peaks as a function of frequency, one negative in magnitude and another is positive. The negative peak shifts towards the lower temperature and positive peak is shifted towards the higher temperature as we increase the frequency. To better understand the AC magnetic response under the influence of various perturbations, we have analyzed the polar plot of the complex ac susceptibility for both the harmonics. Our analysis suggests that the studied sample is in vortex glass state, characterized by a collective flux creep state within Beans model and the Kim Anderson model is ruled out.

cond-mat.supr-con↗

arXiv2016

An inter comparison of the upper critical fields (Hc2) of different superconductors - YBa2Cu3O7, MgB2, NdFeAsO0.8F0.2, FeSe0.5Te0.5 and Nb2PdS5

Here we report the comparison of the upper critical fields of different superconductors being calculated by two different theories i.e., Werthamer Helfand Hohenburg (WHH) and Ginzberg Landau (GL). All the samples are synthesized through previously known solid state reaction route. Phase purity is determined from the Rietveld refinement of powder X-Ray diffraction (XRD) data. High field (up to 14Tesla) magneto transport \r{ho}(T)H of different superconductors is studied to estimate their upper critical field (Hc2). The present inter comparison covers from Cuprates (YBa2Cu3O7) - Borides (MgB2) - Fe pnictides (NdFeAsO0.8F0.2) and chalcogenides (FeSe0.5Te0.5) to robust Nb2PdS5. The upper critical fields [Hc2(T)] at zero temperature are calculated by extrapolating the data using GL and WHH equations.

cond-mat.supr-con↗