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Nilotpal Ghosh

VIT University, Physics, Faculty Member

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Phone: 00914439931321
Address: Physics Department, School of Advanced Sciences, VIT University, Chennai Campus, Vanderlur-Kelambakkam Road, Chennai-6000048

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Alexander Kordyuk

Mojammel Rahaman

Christoph Nacke

University of Copenhagen

Jenny Wooldridge

National Physical Laboratory, United Kingdom

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Papers by Nilotpal Ghosh

Kohler's rule in Ba1􀀀xKxFe2As2

The validity of Kohler's rule has been investigated in Ba 1−x K x Fe 2 As 2 single crystals for x... more The validity of Kohler's rule has been investigated in Ba 1−x K x Fe 2 As 2 single crystals for x = 0.0 and x ∼ 0.02 grown by the self flux growth method using excess FeAs as flux. A sharp peak observed in specific heat measurement around ∼136 K has been attributed to a structural transition accompanying the spin density wave (SDW) transition. An additional slope change in the resistivity profile at 0 and 6 T is observed around 70 K in the K containing sample. Measurement of magnetoresistance as a function of magnetic field (B) up to 9 T indicates that Kohler's rule is obeyed only below 50 K for x ∼ 0.02 but it is not obeyed for x = 0.0. Based on Hall effect measurements the observed difference between the pristine and K doped samples is rationalized.

Pressure-induced superconductivity in BaFe2As2 single crystal

The evolution of pressure-induced superconductivity in single crystal as well as polycrystalline ... more The evolution of pressure-induced superconductivity in single crystal as well as polycrystalline samples of BaFe2As2 have been investigated through temperature-dependent electrical resistivity studies in the 0-7 GPa pressure range. While the superconducting transition remains incomplete in the polycrystalline sample, a clear pressure-induced superconductivity with zero resistivity at the expense of magnetic transition, associated with spin density wave (SDW), is observed in the single-crystal sample. The superconducting transition temperature (TC) is seen to increase upto a moderate pressure of about ∼ 1.5 GPa and decreases monotonically beyond this pressure. The SDW transition temperature TSDW decreases rapidly with increasing pressure and vanishes above ∼ 1.5GPa.

Heisenberg-Like Critical Properties and Magnetocaloric Effect in Lead Doped NdMnO3 Single Crystal

Your article is protected by copyright and all rights are held exclusively by Springer Science +B... more Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media New York. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Magnetic memory effect in chelated zero valent iron nanoparticles

We report the study of nonequilibrium magnetic behavior of air stable zero valent iron nanopartic... more We report the study of nonequilibrium magnetic behavior of air stable zero valent iron nanoparticles synthesized in presence of N-cetyl-N,N,N-trimethyl ammonium bromide chelating agent. X-ray photoelectron spectroscopy study has suggested the presence of iron oxides on nZVI surfaces. Zerofield-cooled and field-cooled magnetization measurements have been carried out at 20-300 K and 100 Oe. For field-cooled measurements with 1 h stops at 200, 100 and 50 K when compared with the warming cycle, we found the signature of magnetic memory effect. A study of magnetic relaxation at the same temperatures shows the existence of two relaxation times.

Critical properties of the double-exchange ferromagnet Nd0.6Pb0.4MnO3

Physical Review B, 2003

Results of a study of dc-magnetization M(T, H), performed on a Nd0.6Pb0.4MnO3 single crystal in t... more Results of a study of dc-magnetization M(T, H), performed on a Nd0.6Pb0.4MnO3 single crystal in the temperature range around T_C (Curie temperature) which embraces the critical region | epsilon | = |T -T_C |/T_C <= 0.05 are reported. The magnetic data analyzed in the critical region using the Kouvel-Fisher method give the values for the T_C =156.47 +/- 0.06 K and the critical exponents, beta = 0.374 +/- 0.006 (from the temperature dependence of magnetization), and gamma = 1.329 +/- 0.003 (from the temperature dependence of initial susceptibility). The critical isotherm M(T_C, H) gives delta = 4.547 +/- 0.1. Thus the scaling law gamma+beta=delta beta is fulfilled. The critical exponents obey the single scaling-equation of state M(H, epsilon) = epsilon^b f_+/- (H/epsilon^(beta + gamma)) where, f_+ for T > T_C and f_- for T< T_C. The exponent values are very close to those expected for the universality class of 3D Heisenberg ferromagnets with short-range interactions.

Effect of rare-earth-site cations on the physical properties of La0.7-y Ndy Pb0.3 Mn O3 single crystals

Physical Review B, 2004

Single crystals of La 0.7−y Nd y Pb 0.3 MnO 3 with different y are grown by flux growth technique... more Single crystals of La 0.7−y Nd y Pb 0.3 MnO 3 with different y are grown by flux growth technique. The influence of change in average cationic radius ͑͗r A ͒͘ and cation size disorder ͑ 2 ͒ on the transport and magnetic properties of these crystals due to the presence of different cations (La and Nd) on the rare-earth ͑R͒ site is studied. Curie temperature T C and metal-insulator transition temperature T MI are sensitive to the R site occupation. The temperature dependence of magnetization of La 0.7 Pb 0.3 MnO 3 is consistent with spin wave excitations according to the Bloch T 3/2 law at zero magnetic field limit. The Nd-based systems follow T 3/2 law only in a certain range of temperature and deviate at low temperatures, which is ascribed to a probably canted ordering of Nd and Mn moments with an antiferromagnetic component at very low temperatures. The values of spin stiffness constants and saturation magnetization vary systematically with changing occupation on the R site. Specific heat measurements of Nd containing samples show a Schottky-like anomaly at low temperature (below 15 K), which increases with the concentration of Nd ions in the lattice. It is concluded that the magnetic properties of manganites with Nd are affected by a tendency for magnetic ordering of the Nd ions.

Growth and characteristics of lead-substituted rare earth manganites

Journal of Crystal Growth, 2005

The growth of R 1Àx Pb x MnO 3 (R ¼ La, Nd, [La,Nd]) single crystals by PbO/PbF 2 flux is describ... more The growth of R 1Àx Pb x MnO 3 (R ¼ La, Nd, [La,Nd]) single crystals by PbO/PbF 2 flux is described with optimized growth conditions. The structure of Nd 1Àx Pb x MnO 3 changes from orthorhombic (x ¼ 0; Pnma) to tetragonal (x ¼ 0:25; P4/mmm) to cubic (x ¼ 0:38; Pm3m) as x increases. These changes are attributed to the progressive removal of inter-octahedral tilting and minimization of octahedral distortion leading to a higher symmetry as doping concentration increases. The T C of this system increases from 110 to 192 K for Pb concentration varying from x ¼ 0:15 to 0.42. The T MI also follows a similar trend. It is observed that hr A i and s 2 are the controlling parameters which influence the transport and magnetic properties of La 0.7Ày Nd y Pb 0.3 MnO 3 . The presence of spin wave excitations are observed prominently in La 0.7 Pb 0.3 MnO 3 at low-temperature which is not so in case of Nd-based compounds. The total magnetic moments of all the Nd-based systems at low-temperature are influenced by Nd. The low-temperature specific heat data of La 0.7Ày Nd y Pb 0.3 MnO 3 is analyzed and contributions of different mechanisms are discussed. It is noticed that the Schottky anomaly is present in specific heat at low-temperature only in Nd-based compounds. r

Heisenberg-like critical properties in ferromagnetic Nd1-xPbxMnO3 single crystals

Journal of Physics-condensed Matter, 2006

Static magnetization for single crystals of insulating Nd 0.85 Pb 0.15 MnO 3 and marginally condu... more Static magnetization for single crystals of insulating Nd 0.85 Pb 0.15 MnO 3 and marginally conducting Nd 0.70 Pb 0.30 MnO 3 has been studied around the ferromagnetic to paramagnetic transition temperature T C . Results of measurements carried out in the critical range |(T − T C )/T C | 0.1 are reported. Critical exponents β and γ for the thermal behaviour of magnetization and susceptibility have been obtained both by modified Arrott plots and the Kouvel-Fisher method. The exponent δ independently obtained from the critical isotherm was found to satisfy the Widom scaling relation δ = γ /β + 1. For both compositions the values of exponents are consistent with those expected for isotropic magnets belonging to the Heisenberg universality class with short-range exchange in three dimensions. Correspondingly, the specific heat displays only a cusp-like anomaly at the critical temperature of these crystals which is consistent with an exponent α < 0. The results show that the ferromagnetic ordering transition in Nd 1−x Pb x MnO 3 in the composition range 0.15 x 0.40 is continuous. This mixed-valent manganite displays the conventional properties of a Heisenberg-like ferromagnet, irrespective of the differing transport properties and in spite of low ordering temperatures T C = 109 and 147.2 K for x = 0.15 and 0.30, respectively.

Continuous phase transition in mixed-valent manganite Nd 0.6Pb 0.4MnO 3

Journal of Magnetism and Magnetic Materials, 2004

The critical behaviour has been investigated in single crystalline Nd 0.6 Pb 0.4 MnO 3 near the p... more The critical behaviour has been investigated in single crystalline Nd 0.6 Pb 0.4 MnO 3 near the paramagnetic to ferromagnetic transition temperature (T C ) by static magnetic measurements. The values of T C and the critical exponents b; g and d are estimated by analysing the data in the critical region. The exponent values are very close to those expected for 3D Heisenberg ferromagnets with short-range interactions. Specific heat measurements show a broad cusp at T C (i.e., exponent ao0) being consistent with Heisenberg-like behaviour. r

Electron paramagnetic resonance studies of the insulating ferromagnetic manganite Nd 0.8Pb 0.2MnO 3 above the transition temperature

Solid State Communications, 2002

Electron paramagnetic resonance studies of the insulating ferromagnetic manganite Nd 0.8 Pb 0.2 M... more Electron paramagnetic resonance studies of the insulating ferromagnetic manganite Nd 0.8 Pb 0.2 MnO 3 above the transition temperature Abstract Single crystals of Nd 1−x Pb x MnO 3 with x=0.2 are grown by high temperature solution growth technique using PbO-PbF 2 flux. Magnetization studies on the samples show a transition to a ferromagnetic state below T c ∼ 125 K and the resistivity measurements show it to be an insulator throughout the temperature range 50 -300 K. Electron Paramagnetic Resonance studies have been performed for T > T C with a view to comparing the results with those on metallic ferromagnetic manganites. The temperature dependence of various parameters like g-value, linewidth and intensity has been studied in the temperature range 150 -300 K. It is found that they behave in a manner similar to that exhibited by metallic ferromagnetic manganites.

Crystal growth, structural and magnetic properties of Nd 1− x Pb x MnO 3

Journal of Magnetism and Magnetic Materials, 2003

Single crystals of Nd1− xPbxMnO3 with various dopant concentrations (x= 0.15, 0.2, 0.3, 0.4 and 0... more

Transport and magnetic properties of Nd1-xPbxMnO3 single crystals

Journal of Applied Physics, 2004

Transport and magnetic properties of flux-grown Nd1-xPbxMnO3 single crystals (x =0.15-0.5) are st... more Transport and magnetic properties of flux-grown Nd1-xPbxMnO3 single crystals (x =0.15-0.5) are studied in the temperature range 300-77K and 280-2K, respectively. Magnetization measurements with a superconducting quantum interference device confirm a paramagnetic to ferromagnetic transition around 110, 121, 150, 160, and 178K for x =0.15, 0.2, 0.3, 0.4, and 0.5, respectively. Four probe resistivity measurements at low temperatures show a monotonic increase for x =0.15 which represents a ferromagnetic insulating (FMI) phase. For Nd0.8Pb0.2MnO3 there is a slope change present in the resistivity profile at 127K where metal to insulator transition (MI) sets in. For x =0.3 this MI transition is more prominent. However, both these samples have FMI phase at low temperature. When the concentration of lead increases (x >0.3) the sample displays a clear insulator to metal transition with a low temperature ferromagnetic metallic phase. On the basis of these measurements we have predicted the phase diagram of Nd1-xPbxMnO3. Magnetization measurements by a vibration sample magnetometer point out the appreciable differences between zero field cooled and field cooled profiles below the ferromagnetic to paramagnetic transition temperature for all x. These are indicative of magnetic frustration.

Influence of dopant concentration on the structure and physical properties of Nd 1 - x Pb x MnO 3 single crystals

Journal of Solid State Chemistry, 2005

The structure of Nd 1Àx Pb x MnO 3 crystal for x ¼ 0:25 is determined at room temperature by sing... more The structure of Nd 1Àx Pb x MnO 3 crystal for x ¼ 0:25 is determined at room temperature by single-crystal X-ray diffraction. The structural refinement reveals that the crystal is tetragonal with space group P4=mmm; Z ¼ 4 and R of 8.3%: The lattice parameters are a ¼ 7:7652ð1Þ Å , c ¼ 3:884ð1Þ Å and a ¼

Low temperature transport and specific heat studies of Nd 1− x Pb x MnO 3 single crystals

Journal of Physics-condensed Matter, 2008

Electrical transport and specific heat properties of Nd_{1-x}Pb_{x}MnO_{3} single crystals for 0.... more Electrical transport and specific heat properties of Nd_{1-x}Pb_{x}MnO_{3} single crystals for 0.15 < x 0.5 have been studied in low temperature regime. The resistivity in the ferromagnetic insulating (FMI) phase for x < 0.3 has an activated character. The dependence of the activation gap Delta on doping x has been determined and the critical concentration for the zero-temperature metal-insulator transition was determined as x_{c} ~ 0.33. For a metallic sample with x=0.42, a conventional electron-electron (e-e) scattering term proportional T^{2} is found in the low-temperature electrical resistivity, although the Kadowaki-Woods ratio is found to be much larger for this manganite than for a normal metal. For a metallic sample with x=0.5, a resistivity minimum is observed for x= 0.5. The effect is attributed to weak localization and can be described by a negative T^{1/2} weak-localization contribution to resistivity for a disordered three-dimensional electron system. The specific heat data have been fitted to contributions from free electrons (gamma), spin excitations (beta_{3/2}), lattice and a Schottky-like anomaly related to the rare-earth magnetism of the Nd ions. The value of gamma is larger than for normal metals, which is ascribed to magnetic ordering effects involving Nd. Also, the Schottky-like anomaly appears broadened and weakened suggesting inhomogeneous molecular fields at the Nd-sites.

Surface morphological study of flux grown lead doped rare-earth manganite single crystals

Journal of Crystal Growth, 2005

Rare-earth manganites with divalent doping have attracted attention because of their interesting ... more Rare-earth manganites with divalent doping have attracted attention because of their interesting physical phenomena. Manganites, doped with divalent lead, are grown from solvent PbO-PbF 2 . Single crystals of R 1Àx Pb x MnO 3 and mixed rare-earth (R y R 0 1Ày ) 1Àx Pb x MnO 3 , where R 0 , R ¼ La, Nd and Pr are grown with different values of x using eutectic composition of PbO: PbF 2 as solvent. Growth temperature can then be significantly reduced. Optimized charge-to-flux ratio 1:6 yields large crystals with dimension up to 4 Â 3 Â 2 mm 3 . A variety of surface features such as hillocks, micro and macro step patterns, dendrites as well as clear featureless surfaces are observed on as-grown crystals. Clear surfaces reveal that growth occurred predominantly by two-dimensional layer growth mechanism. The hillocks might have originated at the site of screw dislocation, which suggests the growth mechanism at low supersaturation. Hopper growth observed on a few crystals is suggestive of unstable growth. Optimum growth parameters are employed to achieve better yield and good quality crystals. r

Influence of dopant concentration on the structure and physical properties of Nd{sub 1-x}PbâMnOâ single crystals

Journal of Solid State Chemistry, 2005

The structure of Nd 1Àx Pb x MnO 3 crystal for x ¼ 0:25 is determined at room temperature by sing... more The structure of Nd 1Àx Pb x MnO 3 crystal for x ¼ 0:25 is determined at room temperature by single-crystal X-ray diffraction. The structural refinement reveals that the crystal is tetragonal with space group P4=mmm; Z ¼ 4 and R of 8.3%: The lattice parameters are a ¼ 7:7652ð1Þ Å , c ¼ 3:884ð1Þ Å and a ¼

Colossal electroresistance in the ferromagnetic insulating state of single crystal Nd0.7Pb0.3MnO3

Physical Review B, 2007

Colossal electroresistance (CER) has been observed in the ferromagnetic insulating (FMI) state of... more Colossal electroresistance (CER) has been observed in the ferromagnetic insulating (FMI) state of a manganite. Notably, the CER in the FMI state occurs in the absence of magnetoresistance (MR). Measurements of electroresistance (ER) and current induced resistivity switching have been performed in the ferromagnetic insulating state of a single crystal manganite of composition Nd$_0.7$Pb$_0.3$MnO$_3$ (NPMO30). The sample has a paramagnetic to ferromagnetic (Curie) transition temperature, Tc = 150 K and the ferromagnetic insulating state is realized for temperatures, T <~ 130 K. The colossal electroresistance, arising from a strongly nonlinear dependence of resistivity ($\rho$) on current density (j), attains a large value ($\approx 100%$) in the ferromagnetic insulating state. The severity of this nonlinear behavior of resistivity at high current densities is progressively enhanced with decreasing temperature, resulting ultimately, in a regime of negative differential resistivity (NDR, d$\rho$/dj < 0) for temperatures <~ 25 K. Concomitant with the build-up of the ER however, is a collapse of the MR to a small value (< 20%) even in magnetic field, H = 7 T. This demonstrates that the mechanisms that give rise to ER and MR are effectively decoupled in the ferromagnetic insulating phase of manganites. We establish that, the behavior of ferromagnetic insulating phase is distinct from the ferromagnetic metallic (FMM) phase as well as the charge ordered insulating (COI) phase, which are the two commonly realized ground state phases of manganites.

Growth and structural investigations on lead-doped NdMnO 3 single crystals

Acta Crystallographica Section A, 2005

Effect of magnetic field on Nd 0.7Pb 0.3MnO 3 single crystal

Journal of Magnetism and Magnetic Materials, 2011

Magnetization and specific heat of Nd 0.7 Pb 0.3 MnO 3 single crystal are studied at applied magn... more Magnetization and specific heat of Nd 0.7 Pb 0.3 MnO 3 single crystal are studied at applied magnetic field. Magnetization measurement at 0.3 T shows ferromagnetic phase below 150 K (T C ) and below 20 K displays an antiferromagnetic component. The latter appears to be destroyed at 4.8 T. This anomalous increase below 50 K is probably due to reorientation of Nd moments at high magnetic field. Heat capacity has been measured at 0-10 T at low temperature. The data have been fitted to contributions from free electrons (g), ferromagnetic spin excitations (b 3/2 ), lattice and a Schottky-like anomaly related to the rare-earth magnetism of the Nd ions. Fitting yields that b 3/2 term is very small at 6 and 10 T because of introducing paramagnetic component in ferromagnetic phase at applied magnetic field. Peak due to Schottky anomaly is observed to be broadened with application of magnetic field and the magnitude of Schottky gap(D Sch ) also increases accordingly.

2 3 Journal of Superconductivity and Novel Magnetism Incorporating Novel Magnetism Observation of ZBCP Above T C at Au/ Y 1 Ba 2 Cu 3 O 7−δ Heterostructure with a Nano Hole: A Possible Evidence for the Cooper Pairs above T C

1 2 3 Your article is protected by copyright and all rights are held exclusively by Springer Scie... more 1 2 3 Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media New York. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Kohler's rule in Ba1􀀀xKxFe2As2

The validity of Kohler's rule has been investigated in Ba 1−x K x Fe 2 As 2 single crystals for x... more The validity of Kohler's rule has been investigated in Ba 1−x K x Fe 2 As 2 single crystals for x = 0.0 and x ∼ 0.02 grown by the self flux growth method using excess FeAs as flux. A sharp peak observed in specific heat measurement around ∼136 K has been attributed to a structural transition accompanying the spin density wave (SDW) transition. An additional slope change in the resistivity profile at 0 and 6 T is observed around 70 K in the K containing sample. Measurement of magnetoresistance as a function of magnetic field (B) up to 9 T indicates that Kohler's rule is obeyed only below 50 K for x ∼ 0.02 but it is not obeyed for x = 0.0. Based on Hall effect measurements the observed difference between the pristine and K doped samples is rationalized.

Pressure-induced superconductivity in BaFe2As2 single crystal

The evolution of pressure-induced superconductivity in single crystal as well as polycrystalline ... more The evolution of pressure-induced superconductivity in single crystal as well as polycrystalline samples of BaFe2As2 have been investigated through temperature-dependent electrical resistivity studies in the 0-7 GPa pressure range. While the superconducting transition remains incomplete in the polycrystalline sample, a clear pressure-induced superconductivity with zero resistivity at the expense of magnetic transition, associated with spin density wave (SDW), is observed in the single-crystal sample. The superconducting transition temperature (TC) is seen to increase upto a moderate pressure of about ∼ 1.5 GPa and decreases monotonically beyond this pressure. The SDW transition temperature TSDW decreases rapidly with increasing pressure and vanishes above ∼ 1.5GPa.

Heisenberg-Like Critical Properties and Magnetocaloric Effect in Lead Doped NdMnO3 Single Crystal

Your article is protected by copyright and all rights are held exclusively by Springer Science +B... more Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media New York. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Magnetic memory effect in chelated zero valent iron nanoparticles

We report the study of nonequilibrium magnetic behavior of air stable zero valent iron nanopartic... more We report the study of nonequilibrium magnetic behavior of air stable zero valent iron nanoparticles synthesized in presence of N-cetyl-N,N,N-trimethyl ammonium bromide chelating agent. X-ray photoelectron spectroscopy study has suggested the presence of iron oxides on nZVI surfaces. Zerofield-cooled and field-cooled magnetization measurements have been carried out at 20-300 K and 100 Oe. For field-cooled measurements with 1 h stops at 200, 100 and 50 K when compared with the warming cycle, we found the signature of magnetic memory effect. A study of magnetic relaxation at the same temperatures shows the existence of two relaxation times.

Critical properties of the double-exchange ferromagnet Nd0.6Pb0.4MnO3

Physical Review B, 2003

Results of a study of dc-magnetization M(T, H), performed on a Nd0.6Pb0.4MnO3 single crystal in t... more Results of a study of dc-magnetization M(T, H), performed on a Nd0.6Pb0.4MnO3 single crystal in the temperature range around T_C (Curie temperature) which embraces the critical region | epsilon | = |T -T_C |/T_C <= 0.05 are reported. The magnetic data analyzed in the critical region using the Kouvel-Fisher method give the values for the T_C =156.47 +/- 0.06 K and the critical exponents, beta = 0.374 +/- 0.006 (from the temperature dependence of magnetization), and gamma = 1.329 +/- 0.003 (from the temperature dependence of initial susceptibility). The critical isotherm M(T_C, H) gives delta = 4.547 +/- 0.1. Thus the scaling law gamma+beta=delta beta is fulfilled. The critical exponents obey the single scaling-equation of state M(H, epsilon) = epsilon^b f_+/- (H/epsilon^(beta + gamma)) where, f_+ for T > T_C and f_- for T< T_C. The exponent values are very close to those expected for the universality class of 3D Heisenberg ferromagnets with short-range interactions.

Effect of rare-earth-site cations on the physical properties of La0.7-y Ndy Pb0.3 Mn O3 single crystals

Physical Review B, 2004

Single crystals of La 0.7−y Nd y Pb 0.3 MnO 3 with different y are grown by flux growth technique... more Single crystals of La 0.7−y Nd y Pb 0.3 MnO 3 with different y are grown by flux growth technique. The influence of change in average cationic radius ͑͗r A ͒͘ and cation size disorder ͑ 2 ͒ on the transport and magnetic properties of these crystals due to the presence of different cations (La and Nd) on the rare-earth ͑R͒ site is studied. Curie temperature T C and metal-insulator transition temperature T MI are sensitive to the R site occupation. The temperature dependence of magnetization of La 0.7 Pb 0.3 MnO 3 is consistent with spin wave excitations according to the Bloch T 3/2 law at zero magnetic field limit. The Nd-based systems follow T 3/2 law only in a certain range of temperature and deviate at low temperatures, which is ascribed to a probably canted ordering of Nd and Mn moments with an antiferromagnetic component at very low temperatures. The values of spin stiffness constants and saturation magnetization vary systematically with changing occupation on the R site. Specific heat measurements of Nd containing samples show a Schottky-like anomaly at low temperature (below 15 K), which increases with the concentration of Nd ions in the lattice. It is concluded that the magnetic properties of manganites with Nd are affected by a tendency for magnetic ordering of the Nd ions.

Growth and characteristics of lead-substituted rare earth manganites

Journal of Crystal Growth, 2005

The growth of R 1Àx Pb x MnO 3 (R ¼ La, Nd, [La,Nd]) single crystals by PbO/PbF 2 flux is describ... more The growth of R 1Àx Pb x MnO 3 (R ¼ La, Nd, [La,Nd]) single crystals by PbO/PbF 2 flux is described with optimized growth conditions. The structure of Nd 1Àx Pb x MnO 3 changes from orthorhombic (x ¼ 0; Pnma) to tetragonal (x ¼ 0:25; P4/mmm) to cubic (x ¼ 0:38; Pm3m) as x increases. These changes are attributed to the progressive removal of inter-octahedral tilting and minimization of octahedral distortion leading to a higher symmetry as doping concentration increases. The T C of this system increases from 110 to 192 K for Pb concentration varying from x ¼ 0:15 to 0.42. The T MI also follows a similar trend. It is observed that hr A i and s 2 are the controlling parameters which influence the transport and magnetic properties of La 0.7Ày Nd y Pb 0.3 MnO 3 . The presence of spin wave excitations are observed prominently in La 0.7 Pb 0.3 MnO 3 at low-temperature which is not so in case of Nd-based compounds. The total magnetic moments of all the Nd-based systems at low-temperature are influenced by Nd. The low-temperature specific heat data of La 0.7Ày Nd y Pb 0.3 MnO 3 is analyzed and contributions of different mechanisms are discussed. It is noticed that the Schottky anomaly is present in specific heat at low-temperature only in Nd-based compounds. r

Heisenberg-like critical properties in ferromagnetic Nd1-xPbxMnO3 single crystals

Journal of Physics-condensed Matter, 2006

Static magnetization for single crystals of insulating Nd 0.85 Pb 0.15 MnO 3 and marginally condu... more Static magnetization for single crystals of insulating Nd 0.85 Pb 0.15 MnO 3 and marginally conducting Nd 0.70 Pb 0.30 MnO 3 has been studied around the ferromagnetic to paramagnetic transition temperature T C . Results of measurements carried out in the critical range |(T − T C )/T C | 0.1 are reported. Critical exponents β and γ for the thermal behaviour of magnetization and susceptibility have been obtained both by modified Arrott plots and the Kouvel-Fisher method. The exponent δ independently obtained from the critical isotherm was found to satisfy the Widom scaling relation δ = γ /β + 1. For both compositions the values of exponents are consistent with those expected for isotropic magnets belonging to the Heisenberg universality class with short-range exchange in three dimensions. Correspondingly, the specific heat displays only a cusp-like anomaly at the critical temperature of these crystals which is consistent with an exponent α < 0. The results show that the ferromagnetic ordering transition in Nd 1−x Pb x MnO 3 in the composition range 0.15 x 0.40 is continuous. This mixed-valent manganite displays the conventional properties of a Heisenberg-like ferromagnet, irrespective of the differing transport properties and in spite of low ordering temperatures T C = 109 and 147.2 K for x = 0.15 and 0.30, respectively.

Continuous phase transition in mixed-valent manganite Nd 0.6Pb 0.4MnO 3

Journal of Magnetism and Magnetic Materials, 2004

The critical behaviour has been investigated in single crystalline Nd 0.6 Pb 0.4 MnO 3 near the p... more The critical behaviour has been investigated in single crystalline Nd 0.6 Pb 0.4 MnO 3 near the paramagnetic to ferromagnetic transition temperature (T C ) by static magnetic measurements. The values of T C and the critical exponents b; g and d are estimated by analysing the data in the critical region. The exponent values are very close to those expected for 3D Heisenberg ferromagnets with short-range interactions. Specific heat measurements show a broad cusp at T C (i.e., exponent ao0) being consistent with Heisenberg-like behaviour. r

Electron paramagnetic resonance studies of the insulating ferromagnetic manganite Nd 0.8Pb 0.2MnO 3 above the transition temperature

Solid State Communications, 2002

Electron paramagnetic resonance studies of the insulating ferromagnetic manganite Nd 0.8 Pb 0.2 M... more Electron paramagnetic resonance studies of the insulating ferromagnetic manganite Nd 0.8 Pb 0.2 MnO 3 above the transition temperature Abstract Single crystals of Nd 1−x Pb x MnO 3 with x=0.2 are grown by high temperature solution growth technique using PbO-PbF 2 flux. Magnetization studies on the samples show a transition to a ferromagnetic state below T c ∼ 125 K and the resistivity measurements show it to be an insulator throughout the temperature range 50 -300 K. Electron Paramagnetic Resonance studies have been performed for T > T C with a view to comparing the results with those on metallic ferromagnetic manganites. The temperature dependence of various parameters like g-value, linewidth and intensity has been studied in the temperature range 150 -300 K. It is found that they behave in a manner similar to that exhibited by metallic ferromagnetic manganites.

Crystal growth, structural and magnetic properties of Nd 1− x Pb x MnO 3

Journal of Magnetism and Magnetic Materials, 2003

Single crystals of Nd1− xPbxMnO3 with various dopant concentrations (x= 0.15, 0.2, 0.3, 0.4 and 0... more

Transport and magnetic properties of Nd1-xPbxMnO3 single crystals

Journal of Applied Physics, 2004

Transport and magnetic properties of flux-grown Nd1-xPbxMnO3 single crystals (x =0.15-0.5) are st... more Transport and magnetic properties of flux-grown Nd1-xPbxMnO3 single crystals (x =0.15-0.5) are studied in the temperature range 300-77K and 280-2K, respectively. Magnetization measurements with a superconducting quantum interference device confirm a paramagnetic to ferromagnetic transition around 110, 121, 150, 160, and 178K for x =0.15, 0.2, 0.3, 0.4, and 0.5, respectively. Four probe resistivity measurements at low temperatures show a monotonic increase for x =0.15 which represents a ferromagnetic insulating (FMI) phase. For Nd0.8Pb0.2MnO3 there is a slope change present in the resistivity profile at 127K where metal to insulator transition (MI) sets in. For x =0.3 this MI transition is more prominent. However, both these samples have FMI phase at low temperature. When the concentration of lead increases (x >0.3) the sample displays a clear insulator to metal transition with a low temperature ferromagnetic metallic phase. On the basis of these measurements we have predicted the phase diagram of Nd1-xPbxMnO3. Magnetization measurements by a vibration sample magnetometer point out the appreciable differences between zero field cooled and field cooled profiles below the ferromagnetic to paramagnetic transition temperature for all x. These are indicative of magnetic frustration.

Influence of dopant concentration on the structure and physical properties of Nd 1 - x Pb x MnO 3 single crystals

Journal of Solid State Chemistry, 2005

The structure of Nd 1Àx Pb x MnO 3 crystal for x ¼ 0:25 is determined at room temperature by sing... more The structure of Nd 1Àx Pb x MnO 3 crystal for x ¼ 0:25 is determined at room temperature by single-crystal X-ray diffraction. The structural refinement reveals that the crystal is tetragonal with space group P4=mmm; Z ¼ 4 and R of 8.3%: The lattice parameters are a ¼ 7:7652ð1Þ Å , c ¼ 3:884ð1Þ Å and a ¼

Low temperature transport and specific heat studies of Nd 1− x Pb x MnO 3 single crystals

Journal of Physics-condensed Matter, 2008

Electrical transport and specific heat properties of Nd_{1-x}Pb_{x}MnO_{3} single crystals for 0.... more Electrical transport and specific heat properties of Nd_{1-x}Pb_{x}MnO_{3} single crystals for 0.15 < x 0.5 have been studied in low temperature regime. The resistivity in the ferromagnetic insulating (FMI) phase for x < 0.3 has an activated character. The dependence of the activation gap Delta on doping x has been determined and the critical concentration for the zero-temperature metal-insulator transition was determined as x_{c} ~ 0.33. For a metallic sample with x=0.42, a conventional electron-electron (e-e) scattering term proportional T^{2} is found in the low-temperature electrical resistivity, although the Kadowaki-Woods ratio is found to be much larger for this manganite than for a normal metal. For a metallic sample with x=0.5, a resistivity minimum is observed for x= 0.5. The effect is attributed to weak localization and can be described by a negative T^{1/2} weak-localization contribution to resistivity for a disordered three-dimensional electron system. The specific heat data have been fitted to contributions from free electrons (gamma), spin excitations (beta_{3/2}), lattice and a Schottky-like anomaly related to the rare-earth magnetism of the Nd ions. The value of gamma is larger than for normal metals, which is ascribed to magnetic ordering effects involving Nd. Also, the Schottky-like anomaly appears broadened and weakened suggesting inhomogeneous molecular fields at the Nd-sites.

Surface morphological study of flux grown lead doped rare-earth manganite single crystals

Journal of Crystal Growth, 2005

Rare-earth manganites with divalent doping have attracted attention because of their interesting ... more Rare-earth manganites with divalent doping have attracted attention because of their interesting physical phenomena. Manganites, doped with divalent lead, are grown from solvent PbO-PbF 2 . Single crystals of R 1Àx Pb x MnO 3 and mixed rare-earth (R y R 0 1Ày ) 1Àx Pb x MnO 3 , where R 0 , R ¼ La, Nd and Pr are grown with different values of x using eutectic composition of PbO: PbF 2 as solvent. Growth temperature can then be significantly reduced. Optimized charge-to-flux ratio 1:6 yields large crystals with dimension up to 4 Â 3 Â 2 mm 3 . A variety of surface features such as hillocks, micro and macro step patterns, dendrites as well as clear featureless surfaces are observed on as-grown crystals. Clear surfaces reveal that growth occurred predominantly by two-dimensional layer growth mechanism. The hillocks might have originated at the site of screw dislocation, which suggests the growth mechanism at low supersaturation. Hopper growth observed on a few crystals is suggestive of unstable growth. Optimum growth parameters are employed to achieve better yield and good quality crystals. r

Influence of dopant concentration on the structure and physical properties of Nd{sub 1-x}PbâMnOâ single crystals

Journal of Solid State Chemistry, 2005

The structure of Nd 1Àx Pb x MnO 3 crystal for x ¼ 0:25 is determined at room temperature by sing... more The structure of Nd 1Àx Pb x MnO 3 crystal for x ¼ 0:25 is determined at room temperature by single-crystal X-ray diffraction. The structural refinement reveals that the crystal is tetragonal with space group P4=mmm; Z ¼ 4 and R of 8.3%: The lattice parameters are a ¼ 7:7652ð1Þ Å , c ¼ 3:884ð1Þ Å and a ¼

Colossal electroresistance in the ferromagnetic insulating state of single crystal Nd0.7Pb0.3MnO3

Physical Review B, 2007

Colossal electroresistance (CER) has been observed in the ferromagnetic insulating (FMI) state of... more Colossal electroresistance (CER) has been observed in the ferromagnetic insulating (FMI) state of a manganite. Notably, the CER in the FMI state occurs in the absence of magnetoresistance (MR). Measurements of electroresistance (ER) and current induced resistivity switching have been performed in the ferromagnetic insulating state of a single crystal manganite of composition Nd$_0.7$Pb$_0.3$MnO$_3$ (NPMO30). The sample has a paramagnetic to ferromagnetic (Curie) transition temperature, Tc = 150 K and the ferromagnetic insulating state is realized for temperatures, T <~ 130 K. The colossal electroresistance, arising from a strongly nonlinear dependence of resistivity ($\rho$) on current density (j), attains a large value ($\approx 100%$) in the ferromagnetic insulating state. The severity of this nonlinear behavior of resistivity at high current densities is progressively enhanced with decreasing temperature, resulting ultimately, in a regime of negative differential resistivity (NDR, d$\rho$/dj < 0) for temperatures <~ 25 K. Concomitant with the build-up of the ER however, is a collapse of the MR to a small value (< 20%) even in magnetic field, H = 7 T. This demonstrates that the mechanisms that give rise to ER and MR are effectively decoupled in the ferromagnetic insulating phase of manganites. We establish that, the behavior of ferromagnetic insulating phase is distinct from the ferromagnetic metallic (FMM) phase as well as the charge ordered insulating (COI) phase, which are the two commonly realized ground state phases of manganites.

Growth and structural investigations on lead-doped NdMnO 3 single crystals

Acta Crystallographica Section A, 2005

Effect of magnetic field on Nd 0.7Pb 0.3MnO 3 single crystal

Journal of Magnetism and Magnetic Materials, 2011

Magnetization and specific heat of Nd 0.7 Pb 0.3 MnO 3 single crystal are studied at applied magn... more Magnetization and specific heat of Nd 0.7 Pb 0.3 MnO 3 single crystal are studied at applied magnetic field. Magnetization measurement at 0.3 T shows ferromagnetic phase below 150 K (T C ) and below 20 K displays an antiferromagnetic component. The latter appears to be destroyed at 4.8 T. This anomalous increase below 50 K is probably due to reorientation of Nd moments at high magnetic field. Heat capacity has been measured at 0-10 T at low temperature. The data have been fitted to contributions from free electrons (g), ferromagnetic spin excitations (b 3/2 ), lattice and a Schottky-like anomaly related to the rare-earth magnetism of the Nd ions. Fitting yields that b 3/2 term is very small at 6 and 10 T because of introducing paramagnetic component in ferromagnetic phase at applied magnetic field. Peak due to Schottky anomaly is observed to be broadened with application of magnetic field and the magnitude of Schottky gap(D Sch ) also increases accordingly.

2 3 Journal of Superconductivity and Novel Magnetism Incorporating Novel Magnetism Observation of ZBCP Above T C at Au/ Y 1 Ba 2 Cu 3 O 7−δ Heterostructure with a Nano Hole: A Possible Evidence for the Cooper Pairs above T C

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