R. C. Budhani

Council of Scientific and Industrial Research (CSIR), New Delhi, New Dilli, NCT, India

Are you R. C. Budhani?

Claim your profile

Publications (197)526.96 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a simple experimental strategy for enhancing the figure-of-merit (ZT) of thermoelectric materials by introducing different kinds of defect features, including nano-porosity, in a range of nano to meso-scale dimensions, employing spark plasma assisted (SPS) reaction sintering of mechanically alloyed nanopowders. This strategy has been experimentally demonstrated in a well known thermoelectric compound, Cu2Se, which is shown to yield a high ZT of 2.1 at 973 K, which is among the highest reported value for this material and shows a ~ 40% increase over its bulk melt-processed counterpart. The main contribution to the enhanced ZT, despite moderate values of power factor, primarily originates from a very small value of thermal conductivity of 0.34 Wm-1K-1. This low thermal conductivity owes its origin primarily to the enhanced low-to-high wavelength phonon scattering by different kinds of defects, in a wide spectrum of nano to meso-scale dimensions, involving microstructural defects generated during high-energy ball milling, abundant nanocrystalline grain boundaries due to very low crystallite size, and more importantly the nano-to-meso scale residual porosity created due to SPS at optimized process parameters. The role of SPS in enhancing the ZT has been discussed and this strategy can also be applied to other thermoelectric materials
    Nano Energy 04/2015; 13:36-46. DOI:10.1016/j.nanoen.2015.02.008 · 10.21 Impact Factor
  • Americal Physical Society March Meeting, USA; 03/2015
  • Source
    Rajni Porwal, R P Pant, R C Budhani
    [Show abstract] [Hide abstract]
    ABSTRACT: Articles you may be interested in Exchange bias effect in epitaxial La0.67Ca0.33MnO3/SrMnO3 thin film structure J. Appl. Phys. 116, 083908 (2014); 10.1063/1.4894281 Anisotropic resistivities in anisotropic-strain-controlled phase-separated La0.67Ca0.33MnO3/NdGaO3(100) films Appl. Phys. Lett. 103, 072407 (2013); 10.1063/1.4818636 Effect of growth oxygen pressure on anisotropic-strain-induced phase separation in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films J. Appl. Phys. 113, 203701 (2013); 10.1063/1.4807293 Annealing assisted substrate coherency and high-temperature antiferromagnetic insulating transition in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films AIP Advances 3, 052106 (2013); 10.1063/1.4804541 Anomalous Hall conductivity and magnetoresistance in epitaxial La 0.67 Ca 0.33 MnO 3−δ thin films J. Appl Temperature (T) dependent microwave absorption measurements are performed on La 0.67 Ca 0.33 MnO 3 (LCMO) epitaxial thin films of thickness 100 and 200 nm in an electron paramagnetic resonance spectrometer operating in X-band. The resonant absorption peak is moni-tored for out-of-plane (H ?) and in-plane (H k) dc magnetic field (H) as the system goes through magnetic ordering. These data suggest a resilient transformation to the ferromagnetic (FM) phase in the vicinity of the Curie temperature (T C), indicative of a phase separation, which is dominant in the thinner film. The saturation magnetization is calculated from SQUID magnetometry on the same film. A pronounced zero-field absorption is seen in H k geometry displaying anomalous growth in 100 nm film at T < T C . This feature is correlated with the magneto-conductivity of the manganite which is colossal in the vicinity of T C in the well-ordered film of thickness 200 nm. Signature of standing spin wave modes is seen in H ? measurements which are analyzed to calcu-late the spin wave stiffness constant D(T) in the limit of zero temperature. The same is also inferred from the decay of equilibrium magnetization in the framework of Bloch law. These studies reveal that a bulk like LCMO is obtained in the fully relaxed thicker films. V C 2015 AIP Publishing LLC.
    Journal of Applied Physics 01/2015; 117(84):13904-1467. DOI:10.1063/1.4905262 · 2.19 Impact Factor
  • Source
    Rajni Porwal, R. P. Pant, R. C. Budhani
    [Show abstract] [Hide abstract]
    ABSTRACT: Temperature (T) dependent microwave absorption measurements are performed on La0.67Ca0.33MnO3 (LCMO) epitaxial thin films of thickness 100 and 200 nm in an electron paramagnetic resonance spectrometer operating in X-band. The resonant absorption peak is monitored for out-of-plane (H?) and in-plane (Hk) dc magnetic field (H) as the system goes through magnetic ordering. These data suggest a resilient transformation to the ferromagnetic (FM) phase in the vicinity of the Curie temperature (TC), indicative of a phase separation, which is dominant in the thinner film. The saturation magnetization is calculated from SQUID magnetometry on the same film. A pronounced zero-field absorption is seen in Hk geometry displaying anomalous growth in 100 nm film at T<TC. This feature is correlated with the magneto-conductivity of the manganite which is colossal in the vicinity of TC in the well-ordered film of thickness 200 nm. Signature of standing spin wave modes is seen in H? measurements which are analyzed to calculate the spin wave stiffness constant D(T) in the limit of zero temperature. The same is also inferred from the decay of equilibrium magnetization in the framework of Bloch law. These studies reveal that a bulk like LCMO is obtained in the fully relaxed thicker films.
    Journal of Applied Physics 01/2015; 117(2015):013904. · 2.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The coexistence of superconductivity and ferromagnetism in the conducting quasi two-dimensional electron gas formed at oxide heterostructures has raised hopes of observing novel phenomenon not seen in conventional semiconductor devices. In this article, we report the observation of a novel magnetic-field assisted transient superconducting state at the interface of LaAlO3 and SrTiO3 at 245 mK. The transient superconducting state appears concomitantly with a Lifshitz transition in the system as a consequence of the interplay between ferromagnetism and superconductivity and the finite relaxation time of in-plane magnetization.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In LaTiO3/SrTiO3 and LaAlO3/SrTiO3 heterostructures, the bending of the SrTiO3 conduction band at the interface forms a quantum well that contains a superconducting two-dimensional electron gas (2-DEG). Its carrier density and electronic properties, such as superconductivity and Rashba spin-orbit coupling can be controlled by electrostatic gating. In this article we show that the Fermi energy lies intrinsically near the top of the quantum well. Beyond a filling threshold, electrons added by electrostatic gating escape from the well, hence limiting the possibility to reach a highly-doped regime. This leads to an irreversible doping regime where all the electronic properties of the 2-DEG, such as its resistivity and its superconducting transition temperature, saturate. The escape mechanism can be described by the simple analytical model we propose.
    Scientific Reports 10/2014; 4:6788. DOI:10.1038/srep06788 · 5.08 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a gradual suppression of the two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface on substitution of chromium at the Al sites. The sheet carrier density at the interface (n□) drops monotonically from ∼2.2 × 10(14) cm(-2) to ∼2.5 × 10(13) cm(-2) on replacing ≈60% of the Al sites by Cr and the sheet resistance (R□) exceeds the quantum limit for localization (h/2e(2)) in the concentrating range 40-60% of Cr. The samples with Cr ⩽40% show a distinct minimum (Tm) in metallic R□(T) whose position shifts to higher temperatures on increasing the substitution. Distinct signatures of Rashba spin-orbit interaction (SOI) induced magnetoresistance (MR) are seen in R□ measured in out of plane field (H⊥) geometry at T ⩽ 8 K. Analysis of these data in the framework of Maekawa-Fukuyama theory allows extraction of the SOI critical field (HSO) and time scale (τSO) whose evolution with Cr concentration is similar as with the increasing negative gate voltage in LAO/STO interface. The MR in the temperature range 8 K ⩽ T ⩽ Tm is quadratic in the field with a +ve sign for H⊥ and -ve sign for H∥. The behaviour of H∥ MR is consistent with Kondo theory which in the present case is renormalized by the strong Rashba SOI at T < 8 K.
    Journal of Physics Condensed Matter 10/2014; 27(12). DOI:10.1088/0953-8984/27/12/125007 · 2.22 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Measurements of magneto-thermopower (S(H, T)) of interfacial delta doped LaTiO$_3$/SrTiO$_3$ (LTO/STO) heterostructure by an iso-structural antiferromagnetic perovskite LaCrO$_3$ are reported. The thermoelectric power of the pure LTO/STO interface at 300 K is $\approx$ 118 $\mu$V/K, but increases dramatically on $\delta$-doping. The observed linear temperature dependence of S(T) over the temperature range 100 K to 300 K is in agreement with the theory of diffusion thermopower of a two-dimensional electron gas. The S(T) displays a distinct enhancement in the temperature range (T $<$ 100 K) where the sheet resistance shows a Kondo-type minimum. We attributed this maximum in S(T) to Kondo scattering of conduction electron by localized impurity spins at the interface. The suppression of S by a magnetic field, and the isotropic nature of the suppression in out-of-plane and in-plane field geometries further strengthen the Kondo model based interpretation of S(H, T).
    Physical Review B 08/2014; 90(7). DOI:10.1103/PhysRevB.90.075133 · 3.66 Impact Factor
  • Himanshu Pandey, R. Prasad, R. C. Budhani
    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
  • P. K. Rout, R. C. Budhani
    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: The dynamics of magnetization (M) reversal and relaxation as a function of temperature (T) are reported in three non-interacting NiFe ring arrays having fixed ring outer diameter and varying widths. Additionally, the dependence of M(H) loop on the angle (θ) between magnetic field (H) and the plane of the rings is addressed. The M(H) loops show a double step transition from onion state (OS) to vortex state (VS) at all temperatures (T = 3 to 300 K) and angles (θ = 0 to 90°). The critical reversal fields HC1 (OS to VS) and HC2 (VS to OS) show a pronounced dependence on T, ring width, and θ. Estimation of the transverse and vortex domain wall energies reveals that the latter is favored in the OS. The OS is also the remanent state in the smallest rings and decays with the effective energy scale (U0/T) of 50 and 32 meV/K at 10 and 300 K, respectively. The robust in-plane anisotropy of magnetization of ring assemblies is established by scaling the M(H) with θ.
    Journal of Applied Physics 03/2014; 115(16). DOI:10.1063/1.4872139 · 2.19 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the effect of δ doping at the LaAlO3/SrTiO3 interface with LaMnO3 monolayers on the photoconducting (PC) state. The PC is realized by exposing the samples to broadband optical radiation of a quartz lamp and 325 and 441 nm lines of a He-Cd laser. Along with the significant modification in electrical transport which drives the pure LaAlO3/SrTiO3 interface from metal-to-insulator with increasing LaMnO3 sub-monolayer thickness, we also observe an enhancement in the photoresponse and relaxation time constant. A possible scenario for the PC based on defect clusters, random potential fluctuations, and large lattice relaxation models, along with the role of structural phase transition in SrTiO3, is discussed. For pure LaAlO3/SrTiO3, the photoconductivity appears to originate from interband transitions between Ti-derived 3d bands which are eg in character and O 2p–Ti t2g hybridized bands. The band structure changes significantly when fractional layers of LaMnO3 are introduced. Here the Mn eg bands (≈1.5 eV above the Fermi energy) within the photoconducting gap lead to a reduction in the photoexcitation energy and a gain in overall photoconductivity.
    Physical Review B 03/2014; 89(12):125127. DOI:10.1103/PhysRevB.89.125127 · 3.66 Impact Factor
  • Source
    Pramod Kumar, Anjana Dogra, R. C. Budhani
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the growth of ultrathin film of Mn doped LaTiO3 on TiO2 terminated SrTiO3 (001) substrate by pulsed laser deposition (PLD) and their electrical transport characteristics including magnetoresistance (MR). Though the replacement of Mn in LaTiO3 at the Ti site in dilute limit does not affect the metallic behaviour of films but variation in resistance is observed. Normalised resistance behaviour is explained on the basis of variation in charge carriers and increased interaction between Mn atoms in the system under investigation.
    03/2014; 1591(1). DOI:10.1063/1.4872961
  • P. K. Rout, R. K. Rakshit, R. C. Budhani
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the Josephson coupling between optimally doped superconducting La1.85Sr0.15CuO4 through the normal metal barrier of La1.85Sr0.15Cu0.97Co0.03O4 (LSCCO). The critical current (Ic) across the junction exists even up to a barrier thickness of 50 nm. The barrier thickness dependence study of Ic yields a large coherence length in LSCCO of (15.2±1.4) nm at 5 K, which indicates the presence of giant proximity effect in such systems.
    03/2014; 1591(1). DOI:10.1063/1.4873019
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The breaking of inversion symmetry combined with polar discontinuity and the presence of strong electronic correlations due to partially filled 3d electronic shell of Ti ions at the LaAlO$_3$/SrTiO$_3$ (LAO/STO) and LaTiO$_3$/SrTiO$_3$ (LTO/STO) interfaces conspire to produce exotic electronic phases. These include macroscopic superconducting and ferromagnetic orders and electronic transport renormalized by strong spin-orbit (S-O) interaction originating to the built-in electrostatic fields at the interface and scattering by localized moments. An important ingredient in this exotic soup of causes and effects is also the quantum paraelectric nature of STO. In order to separate out the contributions of these phenomena from electronic behavior of oxide interfaces, new approaches need to be developed. Here, we present a study of delta doping at LTO/STO interface with iso-structural perovskite of LaCrO$_3$ (LCO) that dramatically alters the properties of the two dimensional electron gas (2DEG) at the interface. The effects include a reduction in sheet-carrier density, prominence of the low temperature resistivity minimum in LAO/STO and LTO/STO 2DEG, enhancement of weak antilocalization below 10 K and observation of a strong anisotropic magnetoresistance (MR). The positive and negative MR for out-of-plane and in-plane field respectively and the field and temperature dependencies of MR suggest Kondo scattering by localized Ti$^{3+}$ moments renormalized by S-O at T < 10 K, with the increase of Cr$^{3+}$ concentration at the interface.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The influence of epitaxial strain on uniaxial magnetic anisotropy of Co$_{2}$FeSi (CFS) and Co$_{2}$MnSi (CMS) Heusler alloy thin films grown on (001) SrTiO$_3$ (STO) and MgO is reported. The in-plane biaxial strain is susceptible to tune by varying the thickness of the films on STO, while on MgO the films show in-plane easy axis for magnetization (\overrightarrow{M}) irrespective of their thickness. A variational analysis of magnetic free energy functional within the Stoner-Wohlfarth coherent rotation model with out-of-plane uniaxial anisotropy for the films on STO showed the presence of magnetoelastic anisotropy with magnetostriction constant $\approx$ (12.22$\pm$0.07)$\times 10^{-6}$ and (2.02$\pm$0.06)$\times 10^{-6}$, in addition to intrinsic magnetocrystalline anisotropy $\approx$ -1.72$\times 10^{6}$ erg/cm$^{3}$ and -3.94$\times 10^{6}$ erg/cm$^{3}$ for CFS and CMS, respectively. The single-domain phase diagram reveals a gradual transition from in-plane to out-of-plane orientation of magnetization with the decreasing film thickness. A maximum canting angle of 41.5$^{\circ}$ with respect to film plane is predicted for the magnetization of the thinnest (12 nm) CFS film on STO. The distinct behaviour of \overrightarrow{M} in the films with lower thickness on STO is attributed to strain-induced tetragonal distortion.
    Applied Physics Letters 01/2014; 104(2):022402. DOI:10.1063/1.4861777 · 3.52 Impact Factor
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report remarkably low residual resistivity, giant residual resistivity ratio, free-electron-like Hall resistivity, and high mobility (≈10^4 cm^2V^−1s^−1) charge transport in epitaxial films of Co2MnSi and Co2FeSi grown on (001) SrTiO3. This unusual behavior is not observed in films deposited on other cubic oxide substrates of comparable lattice parameters. The scaling of the resistivity with thickness of the films allows the extraction of interface conductance, which can be attributed to a layer of oxygen vacancies confined within 1.9 nm of the interface as revealed by atomically resolved electron microscopy and spectroscopy. The high mobility transport observed here at the interface of a fully spin polarized metal is potentially important for spintronics applications.
    Physical Review B 01/2014; 89(2):020401(R). DOI:10.1103/PhysRevB.89.020401 · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report significant enhancement of the thermoelectric figure-of-merit of Mg2Si by double-doping with a combination of Bi, Pb, and Sb as doping elements. Addition of any two of these three elements to Mg2Si increases the electrical conductivity by more than three orders of magnitude at 323 K, irrespective of the doping elements used. However, a corresponding decrease in the Seebeck coefficient is observed in comparison with undoped Mg2Si. Irrespective of the combination of the three elements used for double doping, a figure-of-merit of approximately 0.7 at 873 K is obtained for Mg2Si; this is primarily because of enhancement of the electrical conductivity.
    Journal of Electronic Materials 12/2013; DOI:10.1007/s11664-013-2944-x · 1.68 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The multilayers of [Fe(5Å)/Pt(25 Å)]×15 were prepared by dc magnetron sputtering on 50 Å Pt-buffered MgO substrates. The structural characterization of the multilayers was carried out using X-ray diffraction, X-ray reflectivity. The Secondary ion mass spectroscopy measurement reveals the depth profile and compositional modulations of the multilayer films as per our design specifications. Room temperature magnetic measurements were carried out by using SQUID both in-plane and out-of-plane sample geometry. Magnetization measurements show similar M-H loops for both in-plane and out-of-plane directions of external magnetic field with a coercivity of 190 Oe. These measurements indicate that our samples are magnetically soft and have multifunctional character which is important for making magnetic tunnel junctions.
    58th DAE Solid State Physics Symposium (DAE-SSPS-2013), Thapar University, Patiala, Punjab, India; 12/2013

Publication Stats

2k Citations
526.96 Total Impact Points

Institutions

  • 2012–2015
    • Council of Scientific and Industrial Research (CSIR), New Delhi
      New Dilli, NCT, India
  • 2010–2015
    • National Physical Laboratory - India
      • • Division of Materials Physics and Engineering (NPL)
      • • Quantum Phenomena and Applications Research Area
      Old Delhi, NCT, India
  • 1994–2014
    • Indian Institute of Technology Kanpur
      • Department of Physics
      Cawnpore, Uttar Pradesh, India
  • 1991–2014
    • Brookhaven National Laboratory
      • Physics Department
      New York City, New York, United States
  • 1997–2013
    • Uttar Pradesh Textile Technology Institute
      Cawnpore, Uttar Pradesh, India
  • 2001
    • University of Maryland, College Park
      • Department of Physics
      Maryland, United States
  • 1993
    • University of Nebraska at Lincoln
      Lincoln, Nebraska, United States
  • 1990
    • Emory University
      • Department of Physics
      Atlanta, Georgia, United States