Sudesh Bhalothia | Indian Institute Of Technology, Roorkee (original) (raw)

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Papers by Sudesh Bhalothia

physica status solidi (a), 2014

In the present study, we have shown the effects of ferrocene (FeC 10 H 10 ) addition on the super... more In the present study, we have shown the effects of ferrocene (FeC 10 H 10 ) addition on the superconducting properties of polycrystalline MgB 2 superconductor using transport and magnetic measurements. The addition of FeC 10 H 10 up to 2 wt% in the MgB 2 sample has shown enhanced critical current density, J C in the entire magnetic field region without affecting much the transition temperature. At 10 K, with respect to a pristine MgB 2 sample, J C has improved by a factor of 6.55 at 6 T applied field for 1 wt% FeC 10 H 10 . An improvement in the upper critical field, H C2 and irreversibility field, H irr has also been observed up to 2 wt% addition of FeC 10 H 10 . The value of H C2 ð0Þ as obtained using the Ginzburg-Landau (GL)theory fit of the experimental data increases by almost 2 T for 2 wt% FeC 10 H 10 -added MgB 2 as compared to the pristine samples. From X-ray photoemission spectroscopy (XPS), we observed that the Fe is present in sample in the form of ferromagnetic oxides, Fe 3 O 4 and g-Fe 2 O 3 . These ferromagnetic inclusions provide efficient pinning centers to improve J C (H) behavior. The flux pinning mechanisms present in the FeC 10 H 10 -added samples are described and discussed in this paper.

Journal of Applied Physics, 2012

In the present work, we have studied the effect of Fe composition on the superconducting properti... more In the present work, we have studied the effect of Fe composition on the superconducting properties, such as transition temperature (Tc), upper critical field (Hc2), and irreversibility field (Hirr) of FeSe1/2Te1/2. The polycrystalline samples have been prepared via solid state reaction route with nominal compositions FexSe1/2Te1/2 (x = 0.95, 1.00, 1.05 and 1.10). The x-ray diffraction results show the presence of tetragonal α-FeSe phase with the p4/nmm space group symmetry in all the samples. The zero resistance temperatures, Tczero, measured in zero magnetic field, have been found to be 10.0, 12.4, 12.3, and 11.7 K for x = 0.95, 1.00, 1.05, and 1.10, respectively. The temperature dependence of Hc2(T) and Hirr(T) have been calculated from the magnetoresistance data using the criteria of 90% and 10% of normal state resistivity (ρn) values, respectively. The values of Hc2(0) are 121.3 T, 142.8 T, 82.7 T, and 79.3 T for x = 0.95, 1.00, 1.05, and 1.10, respectively. The possible reason...

Physica C: Superconductivity and its Applications

ABSTRACT In the present work, polycrystalline samples with compositions MgB2 + 3wt% GO + x wt% C6... more ABSTRACT In the present work, polycrystalline samples with compositions MgB2 + 3wt% GO + x wt% C6H8O7 (x = 0, 5 and 10) have been synthesized to study the effect of combined addition of graphene oxide (GO) and citric acid (C6H8O7) on superconducting properties of MgB2. X-ray diffraction studies show the formation of hexagonal crystal structure of MgB2 with space group P6/mmm in all synthesized samples. We observe that the addition of GO in the sample improves the grain connectivity and consequently enhances the critical current density significantly with no substantial change in Tc. However for this sample, there is no significant improvement in Hc2 and Hirr. With the combined addition of GO and citric acid, the JC(H), Hc2 and Hirr are observed to improve substantially as compared to the pristine MgB2 and GO added MgB2 samples. For example JC(10 K, 5 T) of sample x = 10 has improved by a factor of ∼ 15 as compared to pure MgB2 sample and by a factor of ∼ 5.5 as compared to the x = 0 sample. Furthermore, Hc2(0) for x = 10 sample has enhanced by 13 T as compared to pure MgB2 while it has increased by ∼ 10 T in comparison to x = 0 sample. Enhanced flux pinning has been observed with the combined addition of GO and citric acid.

Physica C: Superconductivity and its Applications

ABSTRACT In this paper, the effects of addition of (i) graphene oxide (GO), (ii) a series of rare... more ABSTRACT In this paper, the effects of addition of (i) graphene oxide (GO), (ii) a series of rare-earth (RE, RE = La, Sm, Eu, Gd, Tb and Ho) oxides (REO) and (iii) a mixture of GO and rare-earth oxides (GO + REO) on the superconducting properties of MgB2, have been studied with the help of electrical transport and magnetic measurements. All the samples have been prepared following the standard solid-state reaction route. We have used an optimum value of 1 wt% REO and 3 wt% GO for addition on the basis of previous studies. X-ray diffraction studies confirm the formation of hexagonal crystal structure (space group P6/mmm) of MgB2 with small amounts of REBx (x = 4 and 6) and MgO impurity phases in all the synthesized samples. We observe that the critical current density, Jc and upper critical field Hc2(0) improve significantly in the REO-added and GO-added samples with no significant change in critical temperature, Tc. A substantial enhancement in Jc(H) and Hc2(0) is observed with the GO + REO addition in MgB2. The different flux pinning mechanisms in all the samples are studied and it is found that the point pinning is the dominant mechanism in the GO-added samples and grain boundary pinning is the dominant one in the REO added samples. We have seen the combined effect of both types of flux pinning mechanisms in GO + REO added MgB2.

Physica C: Superconductivity, 2013

Spin excitations are one of the top candidates for mediating electron pairing in unconventional s... more Spin excitations are one of the top candidates for mediating electron pairing in unconventional superconductors. Their coupling to superconductivity is evident in a large number of systems, by the observation of an abrupt redistribution of magnetic spectral weight at the superconducting transition temperature, Tc, for energies comparable to the superconducting gap. Here we report inelastic neutron scattering measurements on Fe-based superconductors, Fe1−x(Ni/Cu)xTe0.5Se0.5, that emphasize an additional signature. The overall shape of the low energy magnetic dispersion changes from two incommensurate vertical columns at T ≫ Tc to a distinctly different U-shaped dispersion at low temperature. Importantly, this spectral reconstruction is apparent for temperature up to ∼ 3Tc. If the magnetic excitations are involved in the pairing mechanism, their surprising modification on the approach to Tc demonstrates that strong interactions are involved.

Superconductor Science and Technology, 2013

In the present paper we report the effect of graphene oxide (GO) doping on the structural and sup... more In the present paper we report the effect of graphene oxide (GO) doping on the structural and superconducting properties of MgB 2. Bulk polycrystalline samples have been synthesized via a solid state reaction route with compositions MgB 2 + x wt% of GO (x = 0, 1, 2, 3, 5, 7 and 10) by sintering at ∼850 • C in a reducing atmosphere of Ar/H 2 (9:1). The x-ray diffraction results confirm the formation of the MgB 2 phase in all samples, together with traces of a MgO impurity phase. The XRD data results also show substitution of carbon for boron, but in the present case the actual amount of carbon substituting for boron is very small as compared to other carbon sources. A substantial improvement in the critical current density, J c (H), has been observed in the entire magnetic field range (0-8 T) for samples x = 1, 2 and 3 as compared to the undoped sample. In addition to J c (H), marginal improvements in the upper critical field (H c2) and the irreversibility field (H irr) have been observed for the doped samples x = 1, 2 and 3 with respect to pristine MgB 2. Furthermore, a curious result of the present investigation is that there is no change in the superconducting transition temperature (T c) up to a doping level of 10 wt%. The possible mechanisms of flux pinning and correlations between the observed superconducting properties and structural characteristics of the samples have been described and discussed in this paper.

In the present work, polycrystalline samples with compositions MgB2 + 3wt% GO + x wt% C6H8O7 (x =... more In the present work, polycrystalline samples with compositions MgB2 + 3wt% GO + x wt% C6H8O7 (x = 0, 5 and 10) have been synthesized to study the effect of combined addition of graphene oxide (GO) and citric acid (C6H8O7) on superconducting properties of MgB2. X-ray diffraction studies show the formation of hexagonal crystal structure of MgB2 with space group P6/mmm in all synthesized samples. We observe that the addition of GO in the sample improves the grain connectivity and consequently enhances the critical current density significantly with no substantial change in Tc. However for this sample, there is no significant improvement in Hc2 and Hirr. With the combined addition of GO and citric acid, the JC(H), Hc2 and Hirr are observed to improve substantially as compared to the pristine MgB2 and GO added MgB2 samples. For example JC(10 K, 5 T) of sample x = 10 has improved by a factor of ∼ 15 as compared to pure MgB2 sample and by a factor of ∼ 5.5 as compared to the x = 0 sample. ...

physica status solidi (a), 2014

In the present study, we have shown the effects of ferrocene (FeC 10 H 10 ) addition on the super... more In the present study, we have shown the effects of ferrocene (FeC 10 H 10 ) addition on the superconducting properties of polycrystalline MgB 2 superconductor using transport and magnetic measurements. The addition of FeC 10 H 10 up to 2 wt% in the MgB 2 sample has shown enhanced critical current density, J C in the entire magnetic field region without affecting much the transition temperature. At 10 K, with respect to a pristine MgB 2 sample, J C has improved by a factor of 6.55 at 6 T applied field for 1 wt% FeC 10 H 10 . An improvement in the upper critical field, H C2 and irreversibility field, H irr has also been observed up to 2 wt% addition of FeC 10 H 10 . The value of H C2 ð0Þ as obtained using the Ginzburg-Landau (GL)theory fit of the experimental data increases by almost 2 T for 2 wt% FeC 10 H 10 -added MgB 2 as compared to the pristine samples. From X-ray photoemission spectroscopy (XPS), we observed that the Fe is present in sample in the form of ferromagnetic oxides, Fe 3 O 4 and g-Fe 2 O 3 . These ferromagnetic inclusions provide efficient pinning centers to improve J C (H) behavior. The flux pinning mechanisms present in the FeC 10 H 10 -added samples are described and discussed in this paper.

Journal of Applied Physics, 2012

In the present work, we have studied the effect of Fe composition on the superconducting properti... more In the present work, we have studied the effect of Fe composition on the superconducting properties, such as transition temperature (Tc), upper critical field (Hc2), and irreversibility field (Hirr) of FeSe1/2Te1/2. The polycrystalline samples have been prepared via solid state reaction route with nominal compositions FexSe1/2Te1/2 (x = 0.95, 1.00, 1.05 and 1.10). The x-ray diffraction results show the presence of tetragonal α-FeSe phase with the p4/nmm space group symmetry in all the samples. The zero resistance temperatures, Tczero, measured in zero magnetic field, have been found to be 10.0, 12.4, 12.3, and 11.7 K for x = 0.95, 1.00, 1.05, and 1.10, respectively. The temperature dependence of Hc2(T) and Hirr(T) have been calculated from the magnetoresistance data using the criteria of 90% and 10% of normal state resistivity (ρn) values, respectively. The values of Hc2(0) are 121.3 T, 142.8 T, 82.7 T, and 79.3 T for x = 0.95, 1.00, 1.05, and 1.10, respectively. The possible reason...

Physica C: Superconductivity and its Applications

ABSTRACT In the present work, polycrystalline samples with compositions MgB2 + 3wt% GO + x wt% C6... more ABSTRACT In the present work, polycrystalline samples with compositions MgB2 + 3wt% GO + x wt% C6H8O7 (x = 0, 5 and 10) have been synthesized to study the effect of combined addition of graphene oxide (GO) and citric acid (C6H8O7) on superconducting properties of MgB2. X-ray diffraction studies show the formation of hexagonal crystal structure of MgB2 with space group P6/mmm in all synthesized samples. We observe that the addition of GO in the sample improves the grain connectivity and consequently enhances the critical current density significantly with no substantial change in Tc. However for this sample, there is no significant improvement in Hc2 and Hirr. With the combined addition of GO and citric acid, the JC(H), Hc2 and Hirr are observed to improve substantially as compared to the pristine MgB2 and GO added MgB2 samples. For example JC(10 K, 5 T) of sample x = 10 has improved by a factor of ∼ 15 as compared to pure MgB2 sample and by a factor of ∼ 5.5 as compared to the x = 0 sample. Furthermore, Hc2(0) for x = 10 sample has enhanced by 13 T as compared to pure MgB2 while it has increased by ∼ 10 T in comparison to x = 0 sample. Enhanced flux pinning has been observed with the combined addition of GO and citric acid.

Physica C: Superconductivity and its Applications

ABSTRACT In this paper, the effects of addition of (i) graphene oxide (GO), (ii) a series of rare... more ABSTRACT In this paper, the effects of addition of (i) graphene oxide (GO), (ii) a series of rare-earth (RE, RE = La, Sm, Eu, Gd, Tb and Ho) oxides (REO) and (iii) a mixture of GO and rare-earth oxides (GO + REO) on the superconducting properties of MgB2, have been studied with the help of electrical transport and magnetic measurements. All the samples have been prepared following the standard solid-state reaction route. We have used an optimum value of 1 wt% REO and 3 wt% GO for addition on the basis of previous studies. X-ray diffraction studies confirm the formation of hexagonal crystal structure (space group P6/mmm) of MgB2 with small amounts of REBx (x = 4 and 6) and MgO impurity phases in all the synthesized samples. We observe that the critical current density, Jc and upper critical field Hc2(0) improve significantly in the REO-added and GO-added samples with no significant change in critical temperature, Tc. A substantial enhancement in Jc(H) and Hc2(0) is observed with the GO + REO addition in MgB2. The different flux pinning mechanisms in all the samples are studied and it is found that the point pinning is the dominant mechanism in the GO-added samples and grain boundary pinning is the dominant one in the REO added samples. We have seen the combined effect of both types of flux pinning mechanisms in GO + REO added MgB2.

Physica C: Superconductivity, 2013

Spin excitations are one of the top candidates for mediating electron pairing in unconventional s... more Spin excitations are one of the top candidates for mediating electron pairing in unconventional superconductors. Their coupling to superconductivity is evident in a large number of systems, by the observation of an abrupt redistribution of magnetic spectral weight at the superconducting transition temperature, Tc, for energies comparable to the superconducting gap. Here we report inelastic neutron scattering measurements on Fe-based superconductors, Fe1−x(Ni/Cu)xTe0.5Se0.5, that emphasize an additional signature. The overall shape of the low energy magnetic dispersion changes from two incommensurate vertical columns at T ≫ Tc to a distinctly different U-shaped dispersion at low temperature. Importantly, this spectral reconstruction is apparent for temperature up to ∼ 3Tc. If the magnetic excitations are involved in the pairing mechanism, their surprising modification on the approach to Tc demonstrates that strong interactions are involved.

Superconductor Science and Technology, 2013

In the present paper we report the effect of graphene oxide (GO) doping on the structural and sup... more In the present paper we report the effect of graphene oxide (GO) doping on the structural and superconducting properties of MgB 2. Bulk polycrystalline samples have been synthesized via a solid state reaction route with compositions MgB 2 + x wt% of GO (x = 0, 1, 2, 3, 5, 7 and 10) by sintering at ∼850 • C in a reducing atmosphere of Ar/H 2 (9:1). The x-ray diffraction results confirm the formation of the MgB 2 phase in all samples, together with traces of a MgO impurity phase. The XRD data results also show substitution of carbon for boron, but in the present case the actual amount of carbon substituting for boron is very small as compared to other carbon sources. A substantial improvement in the critical current density, J c (H), has been observed in the entire magnetic field range (0-8 T) for samples x = 1, 2 and 3 as compared to the undoped sample. In addition to J c (H), marginal improvements in the upper critical field (H c2) and the irreversibility field (H irr) have been observed for the doped samples x = 1, 2 and 3 with respect to pristine MgB 2. Furthermore, a curious result of the present investigation is that there is no change in the superconducting transition temperature (T c) up to a doping level of 10 wt%. The possible mechanisms of flux pinning and correlations between the observed superconducting properties and structural characteristics of the samples have been described and discussed in this paper.

In the present work, polycrystalline samples with compositions MgB2 + 3wt% GO + x wt% C6H8O7 (x =... more In the present work, polycrystalline samples with compositions MgB2 + 3wt% GO + x wt% C6H8O7 (x = 0, 5 and 10) have been synthesized to study the effect of combined addition of graphene oxide (GO) and citric acid (C6H8O7) on superconducting properties of MgB2. X-ray diffraction studies show the formation of hexagonal crystal structure of MgB2 with space group P6/mmm in all synthesized samples. We observe that the addition of GO in the sample improves the grain connectivity and consequently enhances the critical current density significantly with no substantial change in Tc. However for this sample, there is no significant improvement in Hc2 and Hirr. With the combined addition of GO and citric acid, the JC(H), Hc2 and Hirr are observed to improve substantially as compared to the pristine MgB2 and GO added MgB2 samples. For example JC(10 K, 5 T) of sample x = 10 has improved by a factor of ∼ 15 as compared to pure MgB2 sample and by a factor of ∼ 5.5 as compared to the x = 0 sample. ...