Durgesh Singh

Removal of Organic Pollutants by the Use of Iron(III) Hydroxide-Loaded Marble

Abstract Iron(III) hydroxide-loaded marble (Fe-marble) was studied as an adsorbent to remove phenolic compounds from aqueous solution. The coordination of ligands with the central metal ion occurs through the phenolic oxygen. Sorption and break-through capacities were determined. The effects of pH and concentration were studied. Adsorption remains unaffected in the 2–6 pH range. Fe-marble exhibits good sorption capacities for phenolic compounds, and the adsorption data follow the Langmuir model as well as the Freundlich model. Some experiments were also performed with a view to recovery phenols and create in-situ regeneration of spent adsorbent column. The phenols adsorbed were quantitatively eluted with 1 M NaOH solution. The column can be used for 4–5 cycles consecutively.

Large power factor and anomalous Hall effect and their correlation with observed linear magneto resistance in Co-doped Bi2Se3 3D topological insulator.

Magnetoresistance (MR), thermo power, magnetization and Hall effect measurements have been performed on Co-doped Bi2Se3 topological insulators. The undoped sample shows that the maximum MR as a destructive interference due to a π-Berry phase leads to a decrease of MR. As the Co is doped, the linearity in MR is increased. The observed MR of Bi2Se3 can be explained with the classical model. The low temperature MR behavior of Co doped samples cannot be explained with the same model, but can be explained with the quantum linear MR model. Magnetization behavior indicates the establishment of ferromagnetic ordering with Co doping. Hall effect data also supports the establishment of ferromagnetic ordering in Co-doped Bi2Se3 samples by showing the anomalous Hall effect. Furthermore, when spectral weight suppression is insignificant, Bi2Se3 behaves as a dilute magnetic semiconductor. Moreover, the maximum power factor is observed when time reversal symmetry (TRS) is maintained. As the TRS is broken the power factor value is decreased, which indicates that with the rise of Dirac cone above the Fermi level the anomalous Hall effect and linearity in MR increase and the power factor decreases.

Compensation effects in a correlated insulator Fe1-xNixSi

Transport properties of Nickel (Ni) substituted FeSi are investigated. X-ray diffraction measurement shows that the samples are in single phase with Fe successfully being replaced by Ni. Thermo Electric Power (TEP) at low temperatures is dramatic in FeSi that show a systematic reduction by the incorporation of Nickel. Even though the resistivity down to 2K shows a semiconducting behavior, estimation of energy gap has been an ambiguous one. The effects of TEP are dramatic in the sense that it shows the compensation effects in a more clear fashion. A two band model incorporating a metallic and activated conduction resolves the issues like band gap cleaning at low substitution that eventually introduces states at the Fermi level at a higher substitution of Ni.

Effect of spin fluctuations on the resistivity of LaCrGe3

Resistivity of LaCrGe3 at low temperatures and high magnetic fields is reported for fields upto 12T. Spin fluctuations play an important role in this compound whose TC is 90K. The normal state above TC is anomalous in the sense that a T1/2 term is to be added to the normal phonon contribution [ρ=ρ0+aT+bT1/2] to get a good fit, whose origin is debatable. Magneto resistance (MR) vs. applied field H in PM region confirms the presence of strong spin fluctuations in this material. Effect of magnetic field on resistivity shows marked deviation below 170K. Suppression of resistivity in field up to 12T near TC is observed. A negative magnetoresistance (MR) is seen and is consistent with the ferromagnetic behavior. The resistivity data fitted below 80K could be fitted with an equation ρ(H,T) = ρ0(H) + B(H)*Tn where n varies between 2.3 − 2.4, closed to n=2, signifying the presence of possible spin fluctuation.

Magneto-heat capacity study on Kondo lattice system Ce(Ni1−xCux)2Al3

Heat capacity studies on the Kondo lattice system Ce(Ni1−xCux)2Al3, in the presence of magnetic fields, were reported for x = 0.0−0.4. The physical properties of the intermediate compositions like x = 0.3 and 0.4 were known for their enhanced thermoelectric power and hence have been analysed with an extra interest. It was also shown from the X-ray diffraction that these systems with x = 0.3 and 0.4 were in single phase in terms of sample purity and it stabilized the phases easily with the increase in the Cu doping in the system. The low temperature rise in Cp/T below 10 K under the influence of high magnetic fields was analysed using a multi-level Schottky effect. A gradual decrease of the total angular momentum (J) with the increase of applied magnetic fields indicated a scenario of screening of Ce3+ magnetic moment while simultaneously the system settled for the Fermi liquid state. The screening thus seen was in line with the expectations of electrical conductivity measurements on these samples.

Morphological evolution of Bi2Se3 nanocrystalline materials synthesized by microwave assisted solvothermal method

Structural, morphological and spectroscopic properties of Bi2Se3 nanoparticles synthesized by microwave assisted solvothermal method were investigated systematically. A controlled synthesis of different morphologies by a small variation in synthesis procedure is demonstrated. Powder X-ray diffraction (XRD) confirmed the formation of single phase. Crystallite and particle size reductions were studied with XRD and AFM (Atomic Force Microscopy). Different morphologies such as hexagonal nanoflakes with cross section of around∼6µm, nanoflower and octahedral agglomerated crystals of nearly ∼60 nm size have been observed in scanning electron microscope while varying the microwave assisted synthesis procedures. A significant blue shift observed in diffuse reflectance spectroscopy evidences the energy gap tuning as a result of morphological evolution. The difference in morphology observed in this three fast, facile and scalable synthesis is advantageous for tuning the thermoelectric figure of merit and for probing the surface states of these topological insulators. Low temperature resistivity remains similar for all three variants depicting a 2D character as evidenced by a –lnT term of localization.Structural, morphological and spectroscopic properties of Bi2Se3 nanoparticles synthesized by microwave assisted solvothermal method were investigated systematically. A controlled synthesis of different morphologies by a small variation in synthesis procedure is demonstrated. Powder X-ray diffraction (XRD) confirmed the formation of single phase. Crystallite and particle size reductions were studied with XRD and AFM (Atomic Force Microscopy). Different morphologies such as hexagonal nanoflakes with cross section of around∼6µm, nanoflower and octahedral agglomerated crystals of nearly ∼60 nm size have been observed in scanning electron microscope while varying the microwave assisted synthesis procedures. A significant blue shift observed in diffuse reflectance spectroscopy evidences the energy gap tuning as a result of morphological evolution. The difference in morphology observed in this three fast, facile and scalable synthesis is advantageous for tuning the thermoelectric figure of merit and for probing...

Anomalous low temperature resistivity in CeCr0.8V0.2Ge3

Resistivity (8T) and heat capacity (0T) of CeCr0.8V0.2Ge3 at low temperatures and high magnetic fields are reported. Resistivity curve shows a Kondo like behavior at an anomalously high temperature of 250K. A broad peak at 20K is observed in resistivity. A sharp change in resistivity around 7.3K is due to magnetic ordering mediated by coherence effects. Similar low temperature peak is also observed in heat capacity around 7.2K. A small magnetic field of the order of 1T shifts the peak towards lower temperatures confirming the antiferromagnetic ordering. A broad feature, which appears in resistivity at 20K, is absent in heat capacity. This feature shift towards higher temperatures with magnetic field, and may be due to the partial ferromagnetic ordering or due to geometrical frustration which opposes the magnetic ordering. The system shows a moderate heavy fermion behavior with Sommerfeld coefficient (γ) of 111mJ/mol-K2. Debye temperature of the compound is 250K. Shifting of TN in magnetic fields towards 0...

Coexistence of Kondo effect and Ferromagnetism in Ce1.5Nd1.5Al

The possibility for a coexistence of Kondo effect and ferromagnetism in Ce1.5Nd1.5Al has been studied using heat capacity and resistivity. The sample is of polycrystalline in nature. Heat capacity data confirms the heavy fermion behavior of this compound with a Sommerfeld coefficient γ = 190mJ/mol-K2 and Debye temperature ~ 180K. An upturn in resistivity and heat capacity observed near ~ 24K is attributed to the paramagnetic to ferromagnetic transition as reported. Kondo like behavior is observed below 10K and vanishes for magnetic fields of the order of 2T. Around 60K a prominent jump or cusp like behaviour is seen and observed to be robust against magnetic fields up to 14T. Heat capacity below 20K is found to be consistent with equation Cp (T) = γ T + βT3 + αT3/2e-Δ/T that signifies the presence of a gap in magnon excitation energy of the order of 70K.

Low Temperature Heat Capacity of polycrystalline MnSi

The itinerant helimagnet MnSi has been investigated by heat capacity using relaxation calorimetry in H=0. The paramagnetic to helimagnetic transition temperature Tc is found to be 29.6 K. Low temperature heat capacity data in the range 2-18 K is fitted with a usual electronic and phonon contribution. However, an additional magnetic term T 3/2 needs to be added to witness the role of spin wave excitations in the magnetically ordered state below Tc. As well the energy gap on the order A=1.29 meV in the spin wave spectrum is evidenced. Small value of magnetic coefficient δ = 1.66 mJmol-1K-5/2 hints the itinerant nature of the magnetism in MnSi. Obtained coefficients gives the Debye temperature θD = 534 K and the Sommerfeld coefficient of specific heat γ = 0.0367 Jmol-1K-2. Noteworthy observation is the negative trend in the magnetic part of the entropy after Tc.

Anomalous Hall effect in Cr doped FeSi

Investigations of economically affordable bulk materials for the spin based electronics are in huge demand. In this direction, electrical and Hall transport properties of the polycrystalline Cr doped Kondo insulator FeSi, i.e Fe0.975Cr0.025Si is reported. Well agreement between temperature dependence of the Hall and linear resistivity are observed. The observed minimum at ~19K in the resistivity is attributed to the ferromagnetic transition temperature (TC). Anomalous Hall resistivity is seen in the itinerant ferromagnet, Fe0.975Cr0.025Si well below the TC. The obtained Hall resistivity is comparable with that of the spintronic material Fe0.9Co0.1Si. The present study proves that the electrical transport properties of bulk materials made by low cost elements such as Fe, Cr and Si exhibits large magnetic field effects and are useful for the spintronics applications, unlike spintronics material (Ga, Mn)As that demand higher costs.