Sandip Chatterjee

Bio: Sandip Chatterjee is an academic researcher from Indian Institute of Technology (BHU) Varanasi. The author has contributed to research in topics: Magnetization & Ferromagnetism. The author has an hindex of 22, co-authored 186 publications receiving 1979 citations. Previous affiliations of Sandip Chatterjee include National Sun Yat-sen University & Tata Institute of Fundamental Research.

Structural, optical and magnetic properties of sol–gel derived ZnO:Co diluted magnetic semiconductor nanocrystals: an EXAFS study

Abstract: Structural, local structural, optical and magnetic properties of sol–gel derived Zn1−xCoxO (0 ≤ x ≤ 0.04) nanoparticles have been studied. The crystallite structure, size, and lattice strain have been estimated by X-ray diffraction (XRD) with Rietveld refinement and high-resolution transmission electron microscopy (HRTEM). The small linear increase in lattice parameter ‘a’ and decrease in lattice parameter ‘c’ have been observed which can be attributed to the small distortion of Zn tetrahedron. Extended X-ray Absorption Fine Structure (EXAFS) measurements show that Co-doping creates oxygen vacancies without causing any significant change in the host lattice structure. X-ray Absorption Near Edge Structure (XANES) measurements rule out the presence of metallic Co clusters in the samples. Raman spectroscopy has been employed to study the crystalline quality, structural disorder, and defects in the host lattice. The tetrahedral coordination of the oxygen ions surrounding the zinc ions and wurtzite structure has been studied by FTIR analysis. UV-Vis measurements have been used to study the effect of Co-doping on absorption spectra and hence on the band gap. The band gap initially decreases for low Co-concentration and increases with higher Co-concentration. The PL spectra show six peaks out of which the peak in the ultraviolet (UV) region has been assigned to the near band edge excitonic emission (NBE) and other peaks are related to different defect states. Room temperature ferromagnetism (weak) is observed and magnetization increases with increasing Co-concentration. The grain boundaries, oxygen vacancy and bound magnetic polarons (BMPs) jointly may be responsible for this room temperature ferromagnetism. Variation of resistivity with temperature shows that a thermally activated conduction (Arrhenius) mechanism is valid in the high temperature region whereas Mott's variable-range hopping (VRH) mechanism is valid in the low temperature region.

Structural and optical properties of sol-gel derived nanocrystalline Fe-doped ZnO

Abstract: Effects of Fe doping on the structural, optical and magnetic properties of sol-gel derived Zn1−xFexO (0 ≤ x ≤ 0.06) nanoparticles have been investigated. The single-phased wurtzite structure has been characterized by XRD analysis. The nanocrystalline nature of the samples and their crystallinity has been confirmed by TEM measurements. Raman spectroscopy has been employed to study the crystalline quality and structural disorders. FTIR analysis confirms the wurtzite structure and formation of tetrahedral coordination of the oxygen ions surrounding the zinc ions. UV-Vis measurements show that the band gap is fast blue shifted in lower Fe-concentrations and after that slowly red shifted in higher Fe-concentrations. This may be attributed to the Burstein-Moss effect which is prevailed throughout the range of Fe-doping and sp-d exchange interaction that plays a role in higher Fe-concentration. Magnetic hysteresis measurement (M-H) shows that Zn0.96Fe0.04O exhibits ferromagnetic behavior at room temperature.

Critical exponents of the La0.7Sr0.3MnO3, La0.7Ca0.3MnO3, and Pr0.7Ca0.3MnO3 systems showing correlation between transport and magnetic properties

Abstract: From the low-temperature (down to 10K) dc-magnetization data of the La0.7Sr0.3MnO3 (LSM), La0.7Ca0.3MnO3 (LCM), and Pr0.7Ca0.3MnO3 (PCM) systems, we estimated the critical exponents β, γ, and hence δ from the analysis of the modified Arrot plots. The exponent β estimated for the LCM system is less than that predicted by Heisenberg model and resides within the zone predicted by Ising model while for the LSM sample, β is higher than that predicted from the Heisenberg model which is considered to be due to the presence of dipole-dipole interaction arising from the large spin moment in the LSM system. The magnetization data of the PCM system cannot be fitted to the modified Arrot plots, which suggest highly inhomogeneous ground state even under 5T magnetic field. Both LSM and LCM have almost equal values of γ. Seebeck coefficient data indicate a crossover from higher-temperature n-type to lower-temperature p-type conductivity behavior in both LSM and LCM systems, while the semiconducting PCM system shows p-ty...

The second decade.

Abstract: هديكچ يم ناريا كيزيف شهوژپ هلجم راشتنا زا لاس هد درذگ . تنا رد يتلاوحت تبسانم نيا هب هدش هديد كرادت هلجم راش ، هرامش دادعت شيازفا هلمج نآ زا فذح و راهچ هب هنلااس ياه نيب تلااقم هديكچ تسا يللملا . ارا اب ئ هلاقم زا يياهرامآ ه يم رورم ار هتشذگ لاس هد دنور ،هدش رشتنم و تفايرد ياه مينك . يم ملاعا هلجم نارواد زا يتسرهف راب نيلوا يارب دوش و ياهلاؤس م هلجم يور شيپ رد هك يمه تسا ار يم نايم رد ناگدنناوخ اب ميراذگ . ديما تسا رشتنم مود ةهد رد يرتهب هلجم ميناوتب ناريا كيزيف هعماج يراكمه اب مينك .

Investigations on structural and optical properties of ZnO and ZnO:Co nanoparticles under dense electronic excitations

Abstract: In the present study, the structural, morphological, and optical properties of Co-doped ZnO nanoparticles (NPs) prepared by a sol–gel method before and after dense electronic excitations caused by swift heavy ion irradiation have been reported The pristine and ZnO:Co NPs were irradiated by using a 200 MeV Ag15+ ion beam at a fluence of 5 × 1012 ions per cm2 Structural characterization has been performed using X-ray diffraction (XRD) with Rietveld refinement It shows that the samples are of single phase; grain size and tensile strain has been increased in the ion-irradiated samples Room temperature Raman spectroscopy measurements show that microscopic structural disorders reduce the translational symmetry giving rise to local distortions in the lattice Atomic force microscopic (AFM) studies show prominent grain boundaries and suggest that roughness of the irradiated surfaces increases strongly compared to their pristine counterparts Optical absorption and photoluminescence (PL) studies also reflect the dopant incorporation and swift heavy ion (SHI) irradiation effect on the nanoparticles UV-Vis absorption measurement has been utilized to estimate the optical bandgap of pristine and irradiated ZnO and Co-doped ZnO nanoparticles Enhancement in the PL intensity has been observed in the irradiated samples with respect to their pristine counterparts which can be explained on the basis of the increase of different defect states and Zn–O bonds on the surfaces of the irradiated nanoparticles arising from surface modification Grain boundaries have played an important role in the optical properties (absorption and PL)

The 2021 WHO Classification of Tumors of the Central Nervous System: a summary.

Abstract: The fifth edition of the WHO Classification of Tumors of the Central Nervous System (CNS), published in 2021, is the sixth version of the international standard for the classification of brain and spinal cord tumors. Building on the 2016 updated fourth edition and the work of the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy, the 2021 fifth edition introduces major changes that advance the role of molecular diagnostics in CNS tumor classification. At the same time, it remains wedded to other established approaches to tumor diagnosis such as histology and immunohistochemistry. In doing so, the fifth edition establishes some different approaches to both CNS tumor nomenclature and grading and it emphasizes the importance of integrated diagnoses and layered reports. New tumor types and subtypes are introduced, some based on novel diagnostic technologies such as DNA methylome profiling. The present review summarizes the major general changes in the 2021 fifth edition classification and the specific changes in each taxonomic category. It is hoped that this summary provides an overview to facilitate more in-depth exploration of the entire fifth edition of the WHO Classification of Tumors of the Central Nervous System.

Intermediate-spin state and properties of LaCoO_3

Abstract: The electronic structure of the perovskite LaCoO$_3$ for different spin states of Co ions was calculated in the LDA+U approach. The ground state was found to be a nonmagnetic insulator with Co ions in a low-spin state. Somewhat higher in energy we found two intermediate-spin states followed by a high-spin state at significantly higher energy. The calculation results show that Co 3$d$ states of $t_{2g}$ symmetry form narrow bands which could easily localize whilst $e_g$ orbitals, due to their strong hybridization with the oxygen 2$p$ states, form a broad $\sigma^*$ band. With the increase of temperature which is simulated by the corresponding increase of the lattice parameter, the transition from the low- to intermediate-spin states occurs. This intermediate-spin (occupation $t_{2g}^5e_g^1$) can develop an orbital ordering which can account for the nonmetallic nature of LaCoO$_3$ at 90 K$<$T$<$500 K. Possible explanations of the magnetic behavior and gradual insulating-metal transition are suggested.