arXiv subjects

Anand Pal

Publications and source records attributed to Anand Pal.

At least 19 recordsLinked to original sources

arXiv2025

A Dimensionally Consistent Size-Strain Plot Method for Crystallite Size and Microstrain Estimation

X-ray diffraction (XRD) peak broadening analysis remains a cornerstone for quantifying crystallite size and lattice microstrain in materials. Among various approaches, the Size Strain Plot (SSP) method is widely employed for its conceptual simplicity and ease of use. However, this study reveals that the equation most commonly applied in SSP analysis is dimensionally inconsistent, a critical flaw that has gone largely unnoticed and replicated across decades of materials research. This pervasive error raises concerns about the validity of a significant body of published microstructural data. By tracing the historical origin of the misformulated equation, we demonstrate how a seemingly minor oversight evolved into a widely accepted standard practice within the field. We then present a dimensionally consistent formulation that restores physical meaning and analytical reliability to the SSP method. The corrected framework re-establishes the SSP approach as a robust and physically valid tool for XRD-based microstructural characterization. \en

cond-mat.mtrl-sci↗

arXiv2024

Impact of Non-Standard Unicode Characters on Security and Comprehension in Large Language Models

The advancement of large language models has significantly improved natural language processing. However, challenges such as jailbreaks (prompt injections that cause an LLM to follow instructions contrary to its intended use), hallucinations (generating incorrect or misleading information), and comprehension errors remain prevalent. In this report, we present a comparative analysis of the performance of fifteen distinct models, with each model undergoing a standardized test comprising 38 queries across three key metrics: jailbreaks, hallucinations, and comprehension errors. The models are assessed based on the total occurrences of jailbreaks, hallucinations, and comprehension errors. Our work exposes these models' inherent vulnerabilities and challenges the notion of human-level language comprehension of these models. We have empirically analysed the impact of non-standard Unicode characters on LLMs and their safeguarding mechanisms on the best-performing LLMs, including GPT-4, Gemini 1.5 Pro, LlaMA-3-70B, and Claude 3 Opus. By incorporating alphanumeric symbols from Unicode outside the standard Latin block and variants of characters in other languages, we observed a reduction in the efficacy of guardrails implemented through Reinforcement Learning Human Feedback (RLHF). Consequently, these models exhibit heightened vulnerability to content policy breaches and prompt leakage. Our study also suggests a need to incorporate non-standard Unicode text in LLM training data to enhance the capabilities of these models.

cs.CL↗

arXiv2022

Comments on 'X-ray analysis of ZnO nanoparticles by Williamson Hall and size-strain plot methods' Solid State Sciences 13 (2011) 251-256

The equation for the size strain plot methods reported by A. Khorsand Zak et al. (Solid State Sci. 13 (2011), 251) does not follow the dimensional homogeneity, consequently leading to an inaccurate estimation of the crystallite size and strain values of the materials under investigation and the dimensions of the obtained parameters. We also perceived an error in the values of crystallite size and strain reported by the authors using the size-strain plot method. We will discuss the importance of dimensional analysis and its repercussions on the estimated values and the units of parameters.

cond-mat.mtrl-sci↗

arXiv2016

Metallic monoclinic phase in VO$_2$ induced by electrochemical gating: in-situ Raman study

We report in-situ Raman scattering studies of electrochemically top gated VO$_2$ thin film to address metal-insulator transition (MIT) under gating. The room temperature monoclinic insulating phase goes to metallic state at a gate voltage of 2.6 V. However, the number of Raman modes do not change with electrolyte gating showing that the metallic phase is still monoclinic. The high frequency Raman mode A$_g$(7) near 616 cm$^{-1}$ ascribed to V-O vibration of bond length 2.06 Å~ in VO$_6$ octahedra hardens with increasing gate voltage and the B$_g$(3) mode near 654 cm$^{-1}$ softens. This shows that the distortion of the VO$_6$ octahedra in the monoclinic phase decreases with gating. The time dependent Raman data at fixed gate voltages of 1 V (for 50 minute, showing enhancement of conductivity by a factor of 50) and 2 V (for 130 minute, showing further increase in conductivity by a factor of 5) show similar changes in high frequency Raman modes A$_g$(7) and B$_g$(3) as observed in gating. This slow change in conductance together with Raman frequency changes show that the governing mechanism for metalization is more likely to the diffusion controlled oxygen vacancy formation due to the applied electric field.

cond-mat.str-el↗

arXiv2014

Local structural distortions and their role in superconductivity in SmFeAsO$_{1-x}$F$_x$ superconductors

EXAFS studies at the As K edge as a function of temperature have been carried out in SmFeAsO$_{1-x}$F$_x$ ($x$ = 0 and 0.2) compounds to understand the role of local structural distortions superconductivity observed in F doped compound. A significant correlation between thermal variation of local structural parameters like anion height and superconducting onset is found in the fluorinated compound. Such a variation in anion height is absent in non-superconducting compound. Increase in Fe-As bond distance just below superconducting onset temperature indicates a similarity in distortions observed in high T$_C$ cuprates and these Fe based superconductors.

cond-mat.supr-con↗

arXiv2014

Evolution of superconductivity in PrFe1-xCoxAsO with x = 0.0 to 1.0

We report the synthesis and physical property characterization of PrFe1-xCoxAsO with x = 0.0 to 1.0. The studied samples are synthesized by solid state reaction route via vacuum encapsulation method. The pristine compound PrFeAsO does not show superconductivity, but rather exhibits a metallic step like transition due to spin density wave ordering of Fe moments below 150 K, followed by another upward step due to anomalous ordering of Pr moments at 12 K. Both the Fe-SDW and Pr-TN temperatures decrease monotonically with Co substitution at Fe site. Superconductivity appears in a narrow range of x from 0.07 to 0.25 with maximum Tc at 11.12 K for x = 0.15. Samples, with x = 0.25 exhibit metallic behavior right from 300 K down to 2 K, without any Fe-SDW or Pr-TN steps in resistivity. In fact, though Fe-SDW decreases monotonically, the Pr-TN is disappeared even with x = 0.02. The magneto transport measurements below 14 Tesla on superconducting polycrystalline Co doped PrFeAsO lead to extrapolated values of the upper critical fields [Hc2(0)] of up to 60 Tesla.

cond-mat.supr-con↗

arXiv2014

Electrical and Magnetic behaviour of PrFeAsO0.8F0.2 superconductor

The superconducting and ground state samples of PrFeAsO0.8F0.2 and PrFeAsO have been synthesised via easy and versatile single step solid state reaction route. X-ray & Reitveld refine parameters of the synthesised samples are in good agreement to the earlier reported value of the structure. The ground state of the pristine compound (PrFeAsO) exhibited a metallic like step in resistivity below 150K followed by another step at 12K. The former is associated with the spin density wave (SDW) like ordering of Fe spins and later to the anomalous magnetic ordering for Pr moments. Both the resistivity anomalies are absent in case of superconducting PrFeAsO0.8F0.2 sample. Detailed high field (up to 12Tesla) electrical and magnetization measurements are carried out for superconducting PrFeAsO0.8F0.2 sample. The PrFeAsO0.8F0.2 exhibited superconducting onset (Tconset) at around 47K with Tc(ρ =0) at 38K. Though the Tconset remains nearly invariant, the Tc(ρ =0) is decreased with applied field, and the same is around 23K under applied field of 12Tesla. The upper critical field (Hc2) is estimated from the Ginzburg Landau equation (GL) fitting, which is found to be ~ 182Tesla. Critical current density (Jc) being calculated from high field isothermal magnetization (MH) loops with the help of Beans critical state model, is found to be of the order of 103 A/cm2. Summarily, the superconductivity characterization of single step synthesised PrFeAsO0.8F0.2 superconductor is presented.

cond-mat.supr-con↗

arXiv2014

Anomalous magnetism of Pr in PrCoAsO

Detailed magnetization and magneto-transport measurements studies are carried out to unearth the anomalous magnetism of Pr in PrCoAsO compound. The studied PrCoAsO sample is single phase and crystallized in the tetragonal structure with space group P4/nmm in analogy of ZrCuSiAs type compounds. Detailed magnetization measurements showed that Co moments in PrCoAsO exhibit weakly itinerant ferromagnetic Co spins ordering at below 80 K with a small magnetic moments of 0.12 muB/f.u. High temperatures Curie-Weiss fit, resulted in effective paramagnetic moment mueff (exp) of 5.91 muB/f.u., which can be theoretically assigned to 3d Co (3.88 muB) and 4f Pr (3.58 muB). Further, a positive Curie- Weiss temperature of 136 K is seen, indicating predominant ferromagnetic interactions in PrCoAsO. Detailed transport measurements showed that PrCoAsO exhibit metallic behavior and negative magneto-resistance below ferro-magnetically (FM) ordered state. Surprisingly, the situation of PrCoAsO is similar to non magnetic La containing LaCoAsO and strikingly different than that as reported for magnetic Nd, Sm and Gd i.e., (Nd/Sm/Gd)CoAsO. The magnetic behavior of PrCoAsO being closed to LaCoAsO and strikingly different to that of (Nd/Sm/Gd)CoAsO is unusual.

cond-mat.supr-con↗

arXiv2013

High field magneto-transport study of YBa2Cu3O7-Agx (x = 0.0 to 0.20)

We report high field (up to 13 Tesla) magneto transport R(T)H] of YBa2Cu3O7 (YBCO):Agx (x= 0.0, 0.1 and 0.2) composites. The transport properties are significantly improved by Ag doping on the insulating grain boundaries of YBCO. Pure and Ag diffused YBCO superconducting samples are synthesized through solid state reaction route. Both pure and Ag doped YBCO are superconducting at below 90K. Though, the Tc (R=0) of YBCO:Ag samples under applied field of 13 Tesla is around 65K, the same is 45K for pure YBCO under same applied field. The upper critical field [Hc2(0)], being estimated from R(T)H is around 70Tesla for pristine sample, and is above 190Tesla for Ag doped samples. The boarding of the resistive transition under applied magnetic field is comparatively less and nearly single step for Ag doped samples, while the same is clearly two step and relatively much larger for the pristine YBCO. The resistive broadening is explained on the basis of changed inter-granular coupling and thermally activated flux flow (TAFF). The TAFF activation energy (U0) is found to be linear with applied magnetic field for all the samples, but with nearly an order of magnitude less value for the Ag doped samples. Summarily, it is shown that inclusion of Ag significantly improves the superconducting performance of YBCO:Ag composites, in particular under applied field.

cond-mat.supr-con↗

arXiv2013

Magnetotransport and thermal properties characterization of 55 K superconductor SmFeAsO0.85F0.15

Correlation between structural/microstructural and magneto-thermal transport properties of FeAs-based SmFeAsO and SmFeAsO0.85F0.15 has been studied in detail. The Rietveld analysis of room temperature powder X-ray diffraction (XRD) data reveals that both the samples are single phase, with very small amount of rare earth impurity in the F doped compound. Electron microscopic investigations show that compounds have layered morphology and structure, with the individual grains being surrounded by amorphous layers. The average grain boundary thickness is ~5 nm. The F free material is found to be magnetic and shows the appearance of Fe spin density wave (SDW) like order at T = 150 K. The F doped compound (SmFeAsO0.85F0.15) shows the occurrence of superconductivity at Tc(R=0, H=0)- 55 K, which decreases to 42 K at magnetic field (H) of 13 kOe. The superconducting transition was also confirmed by DC magnetization and AC susceptibility measurements. The intra-grain critical current density (Jc) calculated using the Bean critical state model is found to be around 5.26 x 10^4 A/cm2 at 5 K in zero field (H=0). The dependence of thermally activated flux flow energy (U/KB) on the applied magnetic field has been observed. AC susceptibility measurements at different amplitude of applied AC drive field confirm the granular nature of the superconducting compound. is confirmed. Both Fe (SDW) at 150K for SmFeAsO and 55K superconductivity in case of SmFeAsO0.85F0.15 sample has confirmed by Specific heat [Cp(T)] measurement too. Further Sm orders anti-ferro-magnetically at 4.5K for non-superconducting and at 3.5K for superconducting samples, also the entropy change is reduced significantly for the later than the former. Summarily complete physical property characterization for both non-superconducting SmFeAsO and 55K superconductor SmFeAsO0.85F0.15 samples is provided and discussed in the current article.

cond-mat.supr-con↗

arXiv2013

Magneto-transport and magnetic susceptibility of SmFeAsO1-xFx (x = 0.0 and 0.20)

Bulk polycrystalline samples, SmFeAsO and the iso-structural superconducting SmFeAsO0.80F0.20 are explored through resistivity with temperature under magnetic field ρ(T, H), AC and DC magnetization (M-T), and Specific heat (Cp) measurements. The Resistivity measurement shows superconductivity for x = 0.20 sample with Tc(onset) ~ 51.7K. The upper critical field, [Hc2(0)] is estimated ~3770kOe by Ginzburg-Landau (GL) theory. Broadening of superconducting transition in magneto transport is studied through thermally activated flux flow in applied field up to 130 kOe. The flux flow activation energy (U/kB) is estimated ~1215K for 1kOe field. Magnetic measurements exhibited bulk superconductivity with lower critical field (Hc1) of ~1.2kOe at 2K. In normal state, the paramagnetic nature of compound confirms no trace of magnetic impurity which orders ferromagnetically. AC susceptibility measurements have been carried out for SmFeAsO0.80F0.20 sample at various amplitude and frequencies of applied AC drive field. The inter-granular critical current density (Jc) is estimated. Specific heat [Cp(T)] measurement showed an anomaly at around 140K due to the SDW ordering of Fe, followed by another peak at 5K corresponding to the antiferromagnetic (AFM) ordering of Sm+3 ions in SmFeAsO compound. Interestingly the change in entropy (marked by the Cp transition height) at 5K for Sm+3 AFM ordering is heavily reduced in case of superconducting SmFeAsO0.80F0.20 sample.

cond-mat.supr-con↗

arXiv2013

Appearance of superconductivity in new BiS2 based layered LaO0.5F0.5BiS2

We report here synthesis, structural, DC magnetization, and transport studies of new BiS2 based layered LaO0.5F0.5BiS2 superconductor [1]. The sample was synthesized by conventional solid state route via vacuum encapsulation technique at 800oC for 12h. LaO0.5F0.5BiS2 crystallizes in tetragonal P4/nmm space group with lattice parameters a = 4.0703(5)Å, c = 13.3902(4)Å. Bulk superconductivity is confirmed with superconducting transition temperature (Tc) of 2.7K by DC magnetization measurements. The Isothermal magnetization (MH) measurements showed closed loops with clear signatures of flux pinning and irreversible behavior. The resistivity measurements confirmed an onset Tc of 2.7K. The magneto-transport ρ(T,H) measurements showed a resistive broadening and decrease in Tc (ρ=0) to lower temperatures with increasing magnetic field. The magnetic phase diagram involving upper critical and irreversibility fields as a function of temperature has been ascertained. Our DC magnetization and electrical transport measurements confirm the appearance of bulk superconductivity in LaO0.5F0.5BiS2 superconductor.

cond-mat.supr-con↗

arXiv2012

Appearance and disappearance of superconductivity in SmFe1-xNixAsO (x = 0.0 to 1.0)

Bulk polycrystalline Ni-substituted SmFe1-xNixAsO (x = 0.0 to 1.0) samples are synthesized by solid state reaction route in an evacuated sealed quartz tube. The cell volume decreases with increase of Ni content in SmFe1-xNixAsO, thus indicating successful substitution of smaller ion Ni at Fe site. The resistivity measurements showed that the spin-density-wave (SDW) transition is suppressed drastically with Ni doping and subsequently superconductivity is achieved in a narrow range of x from 0.04 to 0.10 with maximum Tc of 9K at x = 0.06. For higher content of Ni (x > 0.10), the system becomes metallic and superconductivity is not observed down to 2K. The magneto-transport [R(T)H] measurements exhibited the upper critical field [Hc2(0)] of up to 300kOe. The flux flow activation energy (U/kB) is estimated ~98.37K for 0.1T field. Magnetic susceptibility measurements also confirms bulk superconductivity for x = 0.04, 0.06 and 0.08 samples. The lower critical field (Hc1) is around 100Oe at 2K for x = 0.06 sample. Heat capacity CP(T) measurements exhibited a hump like transition pertaining to SDW in Fe planes at around 150K and an AFM ordering of Sm spins below temperature of 5.4K for ordered Sm spins [TN(Sm)]. Though, the SDW hump for Fe spins disappears for Ni doped samples, the TN (Sm) remains unaltered but with a reduced transition height, i.e., decreased entropy. In conclusion, complete phase diagram of SmFe1-xNixAsO (x = 0.0 to 1.0) is studied in terms of its structural, electrical, magnetic and thermal properties.

cond-mat.supr-con↗

arXiv2012

Anisotropic spin-fluctuations in SmCoPO revealed by 31^P NMR measurement

31^P NMR spectral features in polycrystalline SmCoPO reveal an axially symmetric local magnetic field. At low temperature, the anisotropy of the internal magnetic field increases rapidly, with K_ab increasing faster than that of K_c. The dominant contribution to this anisotropy arises from Sm-4f electron contribution over that of Co-3d. The intrinsic width 2*(Beta) deviates from linearity with respect to bulk susceptibility below 170 K due to the enhancement of (1/T_2)dynamic, which along with the continuous increase of anisotropy in the internal magnetic field is responsible for the wipe out effect of the NMR signal, well above T_C. 1/T_1 shows large anisotropy confirming a significant contribution of Sm-4f electron spin fluctuations to 1/T_1, arising from indirect RKKY type exchange interaction indicating a non-negligible hybridization between Sm-4f orbitals and the conduction band, over the itinerant character of the Co-3d spins. This anisotropy in originates from the orientation dependence of chi"(q,omega). The 3d-spin fluctuations in the ab plane is 2D FM in nature, while along the c-axis, a signature of a weak 2D AFM spin fluctuations superimposed on weak FM spin-fluctuations even in a field of 7 T and far above T_N is observed. The enhancement of this AFM fluctuations of the Co-3d spins along c-axis, at further low temperature is responsible to drive the system to an AFM ordered state.

cond-mat.str-el↗

arXiv2012

High Field (14Tesla) Magneto Transport of Sm/PrFeAsO

We report high field magneto transport of Sm/PrFeAsO. Below spin density wave transition (TSDW), the magneto-resistance (MR) of Sm/PrFeAsO is positive and increasing with decreasing temperature. The MR of SmFeAsO, is found 16%, whereas the same is 21.5% in case of PrFeAsO, at 2.5 K under applied magnetic field of 14 Tesla (T). In case of SmFeAsO, the variation of isothermal MR with field below 20 K is nonlinear at lower magnetic fields (< 2 Tesla) and the same is linear at moderately higher magnetic fields (H \geq 3.5 T). On the other hand PrFeAsO shows almost linear MR at all temperatures below 20 K. The anomalous behavior of MR being exhibited in PrFeAsO is originated from Dirac cone states. The stronger interplay of Fe and Pr ordered moments is responsible for this distinct behavior. PrFeAsO also shows a hump in resistivity (R-T) with possible conduction band (FeAs) mediated ordering of Pr moments at around 12 K. However the same is absent in SmFeAsO even down to 2 K. Our results of high field magneto-transport of up to 14 Tesla brings about clear distinction between ground states of SmFeAsO and PrFeAsO.

cond-mat.supr-con↗

arXiv2012

Single step synthesis of Sr4V2O6Fe2As2: The blocking layer based potential future superconductor

We report synthesis, structural details and transport measurements on Sr4V2O6Fe2As2. Namely the stoichiometric amounts of V2O5 + SrO2 + Sr + 2FeAs are weighed mixed, ground thoroughly and palletized in rectangular form in a glove box in high purity Ar atmosphere. The pellet is further sealed in an evacuated (10-5 Torr) quartz tube and put for heat treatments at 750 and 1150 0C in a single step for 12 and 36 hours respectively. Finally the quartz ampoule is allowed to cool naturally to room temperature. The as synthesized sample is black in color. The compound crystallized in P4/nmm space group with lattice parameters a = b = 3.925A and c = 15.870A. Also seen are some small impurity lines. The compound did not exhibit superconductivity but instead a spin density wave (SDW) like metallic step at around 175 K is seen in R(T) measurements

cond-mat.supr-con↗

arXiv2012

Synthesis and Structural details of BiOCu1-xS: Possible new entrant in series of exotic superconductors?

We report an easy route single step synthesis of BiOCuS with and without Cu deficiency. The title compound is synthesized via solid state reaction route by encapsulation in an evacuated (10-3 Torr) quartz tube. Mixed components of the ingredients in stoichiometric ratio (1/3Bi2O3 +0.34Bi +Cu1-x + S) are pelletized, sealed in evacuated quartz tube and heat treated for 30 hours at 500 0C. Finally the sample is allowed to cool down to room temperature. The resultant compound is black is color and could not hold in pellet form, but is powdered. X-ray diffraction Reitveld analysis is carried out on all three samples of series BiOCu1-xS with x = 0.0, 0.10 and 0.15. These samples crystallize in single phase with space group P4/nmm and with cell parameters as a = 3.868 A and c = 8.557 A for stoichiometric BiOCuS. The volume of the cell slightly increases with an increase in Cu deficiency. The co-ordinate positions are determined by fitting the observed XRD patterns of the studied samples.

cond-mat.supr-con↗

arXiv2012

Synthesis of SmFeAsO by an Easy and Versatile Route and its Physical Property Characterization

We report synthesis, structure, electrical transport and heat capacity of SmFeAsO. The title compound is synthesized by one-step encapsulation of stoichiometric FeAs, Sm, and Sm2O3 in an evacuated (10-5 Torr) quartz tube by prolong (72 hours) annealing at 1100oC. The as synthesized compound is crystallized in tetragonal structure with P4/nmm space group having lattice parameters a = 3.93726(33) A and c = 8.49802(07) A. The resistance (R-T) measurements on the compound exhibited ground state spin-density-wave (SDW)-like metallic steps below 140 K. Heat capacity CP(T) measurements on the title compound, showed an anomaly at around 140 K, which is reminiscent of the SDW ordering of the compound. At lower temperatures the CP(T) shows a clear peak at around 4.5 K. At lower temperature below 20 K, Cp(T) is also measured under an applied field of 7 Tesla. It is concluded that the CP(T) peak at 4.5 K is due to the anti-ferromagnetic(AFM) ordering of Sm3+ spins. These results are in confirmation with ordering of Sm in Sm2-xCexCuO4.

cond-mat.supr-con↗