017917   Singh A;Aswal D K;Sen S;Shah K;Gupta L C; Gupta S K;Sahni V C (Tech Phys and Prototype Engn Div, BARC, Mumbai-400 085) : Effect of substrate temperature on electrical and magnetic properties of epitaxial la 1-x pb x MnO 3 films. Pramana J Phys 2002, 58(5-6), 1065-7.

Epitaxial La_1-xPb_{xMnO3 (LPMO) thin films, grown on (100) SrTiO3 substrates by laser ablation technique at different temperatures between 600 and 850<144>C, have ben characterized for electrical and magnetic properties. The temperature dependence of resistivity showed that the metal-insulator transition temperature (TMI) decrease with increasing substrate temperature, which has been attributed to decrease in Pb content in the films. The YBa2Cu3Ox/La1-xPbx3 heterostructures, exhibiting both superconductivity and ferromagnetism, have been fabricated.}

2 illus, 2 ref

017916   Shukla N N;Prasad R (Phiscs Dep, Indian Institute of Technology, Kanpur-208 016) : Oscillatory interlayer magnetic coupling and induced magnetism in Fe/Nb multilayers. Bull Mater Sci 2003, 26(1), 143-6.

Ab initio calculation of interlayer magnetic coupling has beebn presented for Fe/Nb multilayers using the self-consisten full-potential linearized augmented-plane-wave (FLAPW) method. For this calculation, supercells have been constructed consisting of bcc Fe and Nb multilayers in Fe/Nb/Fe sandwich geometry stacked along (001) direction. In the supercells two Fe layers are separated by Nb layers ranging from 1 to 11 layers. Teh total energy of the system as a function of Nb spacer layer thickness. For each specer layer thickness three calculation have been done corresponding to para, ferro and antiferromagnetic ordering of Fe atoms. The interlayer magnetic coupling is obtaine dform the energy differnece of the systems in which Fe layers are antiferromagnetically and ferromagnetically ordered. It has been found that the interlayer magnetic coupling oscillates with increasing Nb spacer thickness in agreement with the experimental results. The induced magnetic moment is also found to be oscillating with inceasing Nb spacer layer thickness.

4 illus, 1 tables, 15 ref

017915   Shivagan D D;Shirage P M;Pawar S H (School of Energy Studies, Phys Dep, Shivaji Univ, Kolhapur-416 004) : Studies on photoinduced effects in pulse-electrodeposited Ag/Hg-1212/CdSe hetero-nanostructures. Pramana J Phys 2002, 58(5-6), 1183-90.

Metal/Superconductor/semiconductor (Ag/Hg-1212/CdSc_ hetero-nanostructures have been fabricated using pulse-electrodeposition technique and are characterised by X-ray diffraction (XRD), full-width at half-maximum (FWHM) and scanning electron microscopy (SEM) studies. The junction capacitance of Ag/Hg-1212, Hg-1212/CdSe and ag/Hg-1212/CdSe heterojunctions is measured in dark and under laster irradiation at room temperature. The nature of the junction formed and build-in-junction potentials were determined. The increase in carrier concentration across the junction due to photo-irradiation has been observed.

6 illus 16 ref

017914   Shirage P M;Shivagan D D;Pawar S H (School of Energy Studies, Dep of Physics, Shivaji Univ, Kolhapur-416 004) : Effect of laser irradiation on C-V characteristics of electrodeposited Ag/Tl-2223/CdSe hetero-nanostructures. Pramana J Phys 2002, 58(5-6), 1191-8.

One of the innovativ technological directions for the high-temperature superconductors has been persued by fabriction the heteroepitaxial multilayer structures such as superconductor-semiconductor heterostructures. In the investigation, metal/superconductor/semiconductor (Ag/Tl-2223/CdSe) hetero-nanostructures have successfully been fabricated using dc electrodeposttion technique and were characterized by X-ray diffraction (XRD), ful-width at half-maximum (FWHM) and scanning electron microscopy (SEM) studies. The measurement of junction capacitance as a function of biasing voltage was used for the estimation of junction built-in-potential (V_D) and to study the charge distribution in a heterojunction. The Mott-Schottky plots were measured for each junction in dark and under the photo-irradiation. The effect of laser irradiation on C-V characteristics of hetero-nanostructure has been studied.

6 illus, 17 ref

017913   Shetty S;Palkar V R;Pinto R (Dep of Material Sci, Mangalore Univ, Mangalagangothri-574 199) : Size effect study in magnetoelectric BiFeO 3 system. Pramana J Phys 2002, 58(5-6), 1027-30.

Reports for the first time finite size effects on Neel temperature T_N) of magnetoelectric BiFeO₃ system. Novel wet chemical route has been developed to produce fine particles of BiFeO₃ with controlled size and size distribution. Unlike other oxide systems, lattice volume contraction has been observed with decrease in particle size. The decrease in T_N in co-related to unit cell volume contraction occurring with reduction in particle size.

2 illus, 1 table, 5 ref

017912   Shenoy V B (NO, Material Research Centre, Indian Institute of Science, Bangalore-560 012) : Multi-scale modeling strategies in materials science-the quasicontinuum method. Bull Mater Sci 2003, 26(1), 53-62.

The problem of prediction of finite temperature properties of materials poses great computational challenges. The computational treatment of the multitude of length and time scales involved in determining macroscopic properties has been attempted by several workers with varying degrees of success. Review the recently developed quasicontinuum method which is an attempt to bridge the length scales in a single seamless model with the aid of the finite element method. Attments to generalize this method to finite temperatures has been outlined.

7 illus, 14 ref

017911   Shah K;Aswal D K;Singh A;Gupta L C;Gupta S K; Sahni V C (Tech Phys and Prototype Engn Div, , Bombay-500 085) : Colossal magnetoresistance in layred manganite. Pramana J Phys 2002, 58(5-6), 1085-8.

The layered manganite Nd_2-2xSr_1+2xMn₂O₇, with x varying between O and 0.5, has been synthesized using solid-state reaction method. Founds that Nd_2-2xsr_1-2xMn₂O₇ do not form the single-phase layered compound with A₃B₂O₇ structure. Instead, mixtures of various phases, such as, orthorhombic perovskite, i.e., Nd_1-zSr_zMnO₃, layered manganite and unreacted starting compounds, have been obtained. Except for x=0.4, which is found to be an antiferromagnetic insulator, all other x values yielded metal-insulator transition and ferromagnetic ordering.

2 illus, 1 table, 5 ref

017910   Senapati K;Budhani R C (Dep of Phys, Indian Institute of Tech, Kanpur-208 016) : Dynamics of superconducting mixed state in YBa2Cu3O7- /PrBa2Cu3O7- superlattices in radio frequence regime. Pramana J Phys 2002, 58(5-6), 971-4.

Epitaxial multilayers of YBa₂Cu₃O_{7<100> and PrBa2Cu3O7-δ have been deposited on (100) cut SrTiO3 substrates using the technique of pulsed laser deposition. Standard θ-2θ X-ray diffraction measurements on the films showed excellent superlattice reflections. The mixed state of these superlattices has been probed through measurements of radio frequency penetration depth(λ as a function of temperature (T), magnetic field (H) and its orientation (θ) with respect to the planes of the superlattices. These data reflect two-dimensional nature of the mixed state in these systems.}

2 illus, 6 ref

017909   Sen S;Aswal D K;Singh A;Rao T V C;Muthe K P; Vyas J C;Gupta L C;Gupta S K;Sahni V C (Tech Phys and Prototype Engin Div, BARC, Mumbai-400 085) : Prepartation and characterization of MgB2 superconductor. Pramana J Phys 2002, 58(5-6), 867-70.

The MgB₂₂

4 illus, 7 ref

017908   Semwal H K;Bhatt S C;Semwal B S (Dielectric and Ultrasonic Research Laboratory, Physics Dep, H N B Garhwal University, Srinagar-246 174, (Garhwal) Uttaranchal) : Acoustical study of binary liquid mixture of acetic acid and isopropyl sulphide. J pure appl Ultrasonics 2003, 25(1), 6-12.

The Velocity of Ultrasonic wave in binary liquid mixture of Acetic acid and Isopropyl sulphide has been measured at 1, 2, 3, 4, 5, 6 and 7 MHz frequencies at room temperature with the help of ultrasonic interferometer. Isentropic compressibility (Ks), acoustic impedance (Z) and relaxation time have been calculated for the whole composition range for these binary mixtures.

4 illus, 5 tables, 15 ref

017907   Sarkar S;Ramakrishnan S;Grover A K;Tomy C V; Balakrishnan G;Paul M K (Tata Institute of Fundamental Res, , Home Bhabha Road, Mumbai-400 005) : Comparison of thermomagnetic history effects in weakly pinned single crystals of R3Rh4Sn13 (R = Yb, Ca). Pramana J Phys 2002, 58(5-6), 979-83.

A comparative study of the thermomagnetic memory effects of J_c in two weakly pinned low T_c superconductors, Ca₃Rh₄Sn₁₃ (CaRhSn) and Yb₃Rh₄Sn₁₃ (YbRhSN), is presented. In both the systems, the peak effect (PE) phenomenon appears as an order-disorder transformation through stepwise amorph lattice (FLL) However, in CaRHSn, one another disorder-driven transition (Bragg glass (BG) to a vortex glass (VG) in a distinct manner as in a single crystal of high T₂YBa₂Cu₃O_7-δ for H c.

3 illus, 4 ref

017906   Santhanam R;Suresh B;Bala Sundar S;Kannan K (Health and Safety Dep, Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102) : Measurement of radon, thoron progeny concentration in a thorium, uranium handling facility at Kalpakkam. Indian J envir Prot 2001, 21(5), 448-51.

In view of the potential hazard for internal exposure to the occupational workers, measurement of radon, thoron and their daughters in a thorium, uranium - handling facility assumes significance. Presents the results of a detailed study carried out in such a facility by filter paper sampling and alpha detection and analysis of data using the five - count method.

1 tables, 10 ref

017905   Sankar N;Ramachandran K (Dep of Theoretical Physics, Madurai Kamaraj University, Madurai-625 021) : On the symmetry of phosphorous doped ZnSe. Bull Mater Sci 2002, 25(4), 329-34.

The site symmetry of P doped ZnSe is analysed in detail, as the recent experiments suggest two possible symmetries T_d and C_3v. The reduction to C_3v is attributed to the presence of natural impurity, Ga. Our calculations based on molecular model and Green's functions suggest that the symmetry C_3v is possible with ZnSe : P when Jahn Teller distortion of about ″ 0.2 A (towards one of Zn atom) is assumed. This has been supported by other experiments.

2 illus, 7 tables, 15 ref

017904   Sahoo L K;Budhani R C;Kanjilal D;Mehta G K (Dep of Phys, Indian Institute of Technology, Kanpur-208 016) : The non-linear dyanmics of vortices subjected to correlated and random pinning disorders in a quasi-2D superconductor. Pramana J Phys 2002, 58(5-6), 965-9.

Understanding the dynamics of vortex matter subjected to random and correlated pinning disorders in layered superconductors remains a topic of considerable interest. The dynamical behavior of vortices in these systems shows a rich variety of effects due to many competing interactions. Studies the ac response of as-grown as well as heaving-ion-irradiated Tl₂Ba₂CaCu₂O₈ (Tl-2212) thin films by using a micro Hall-probe susceptometer. Finds that the dynamics of vortices in the high-temperature, low-field regime of the H-T phase diagram investigated here depends on the nature of pinning defects. While the decay of screening currents J(t) indicates a glassy behavior in both types of samples, the nature of the glassy phase of different in the two cases. Samples with columnar defects show distinct signature of a Bose glass in the measurement of J(t) and the angular dependence of the irreversibility field (B_irr).

4 illus, 7 ref

017903   Reddy R R;Nazeer Ahammed Y;Rama Gopal K;Abdul Azeem P;Sasikala Devi B (Physics Dep, Sri Krishnadevaraya University, Anantapur-515 003) : Correlation between lattice energy, interionic distance, valance electron plasma energy, electronegativity, bond energy and mean sound velocity for alkali halides. J pure appl Ultrasonics 2003, 25(1), 19-24.

Simple correlations have been established for the estimation of lattice energies of alkali halides directly from interionic distance r_o (A^O), valance electron plasma energy hω_p (eV), Martynov and Bastsanov electronegativity (C_AC_B), Optical electronegativity (Δχ^*) and bond energy (KJ/mol). The estimated lattice energies are in excellent agreement (within ±10%) with the experimental values. These values are used to evaluate mean sound velocities in Kudriavtsev's theory. The merits of the approach are discussed.

2 illus, 2 tables, 21 ref

017902   Razzak A;Bhuiyan A H (Physics Dep, Bangladesh University of Engineering and Technology (BUET), Dhaka-1000, Bangladesh) : DC electrical conduction mechanism in polypropylene-Bijoypur white clay (PP-BWC) composite. Indian J Phys-Pt A 2003, 77(4), 353-7.

Polypropylene-Bijoypur white clay (PP-BWC) composites were prepared at different compositions of PP and BWC of BAngladesh by extrusion technique. Structural change was investigated using X-ray diffractometry (XRD). The dc electrical conduction mechanism of different PP-BWC composites was studied by current-voltage (I-V) characteristic measurements. It is observed that PooleFrenkel type of mechanism is opereative in these materials. The dc conductivity measurement of the different samples was performed in the temperature range 298 K to 400 K. The temperature dependence of electrical conductivity indicates that the conduction is due to thermally activated hopping of charge carriers.

4 illus, 3 tables, 26 ref

017901   Raychaudhuri P;Mitra C;Dorr K;Muller K H; Kobernik G;Pinto R (Phys and Astronomy Dep, Univ of Birmingham, B15 2TT, UK) : Magneto-transport properties of tunnel junction. Pramana J Phys 2002, 58(5-6), 1179-82.

Hole-doped rare-earth manganite La_0.7Ca_0.3MnO₃ and the electron-doped manganite La_0.7Ce_0.3MnO₃ both show a metal-insulator transition around 250 K associated with a ferromagnetic transition and colosal magnetoresistance. In an earlier publication it was reported the rectifying characteristic of La_0.7Ca_0.3MnO₃/SrTiO₃/La_0.7Ce_0.3Mn O₃ tunnel junction at room temperature, showing that it is possible to fabricate a diode out the polaronic insulator regime of doped manganites. Reports the magneto-transport properties of such a tunnel junction above and below the matel-insulator transition. Shows, from the large positive magnetoresistance of the tunnel junction at low temperature, that La_0.7Ce_0.3MnO₃ could be a minority spin carrier ferromagnet. The implication of this observation is discussed.

1 illus, 5 ref

017900   Rayaprol S;Mavani K;Thaker C M;Rana D S; Chakravorty K;Paranjape S K;Ramanadham M;Kulkarni N A;Kuberkar D G (Dep of Phys, Saurashtra Univ, Rajkot) : Structural studies and Tc dependence in La2-xDyxCayBa2Cu4+yOz type mixed oxide superconductors. Pramana J Phys 2002, 58(5-6), 877-80.

A new series of mixed oxide superconductors with the stoichiometric composition La_2-xDy_xCa_yBa₂Cu_4+yO_z (x=0.0 - 0.5, y = 2x) has been studied for structural and superconductiong properties. Earlier studies on La_2-x(Y/Er)_xCa_yBa₂Cu_4+yO_z series, show a strong dependence of Tc on hole concentration (psh). The results of the analysis of the neutron diffraction measurements at room temprerature on x = 0.3 and 0.5 samples are reported. It is intersting to know that Ca substitites for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum Tc is obtained for x = 0.5, Y=1.0 sample (Tc ~ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu_{5Oz (La-2125)}

2 illus, 1 table, 3 ref

017899   Ravi C;Asokamani R (Division of Science and Humanities Dep, MIT Campus, Anna University, Chennai-600 044) : Site preference of Zr in Ti₃Al and phase stability of Ti₂ZrAl. Bull Mater Sci 2003, 26(1), 97-103.

The site preference of Zr atoms in Ti₃Al the and phase stability of Ti₂ZrAl are examined using first-principles electronic structure total energy calculations. Of the sixteen possible ways in which Ti, Zr and Al atoms can be arranged, in the lattice sites corresponding to D0₁₉ structure of Ti₃Al, to obtain Ti₂ZrAl, it is shown that Zr atoms prefer to get substituted at the Ti sites. It is further shown that among the seven crystal structures considered, D0₁₉-like and L1₂-like are the competing ground-state structures of Ti₂ZrAl. The results are in agreement with the experimental results reported in the literature. Calculates values of equilibrium lattice parameters, heat of formation and bulk modulus of Ti₂ZrAl are presented. The basis for the structural stability and bonding are analysed in terms of the density of states. Between the two possible B2-like structures, Ti₂ZrAl shows enhanced stability for the one where Zr is substituted in the Ti sublattice, which again is in agreement with the experimental observation.

5 illus, 2 tables, 36 ref

017898   Ranganathan R;Ray A (Experimental Condensed Matter Phys Div, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Calcutta-700 064) : Ferrites- What is new?. Pramana J Phys 2002, 58(5-6), 995-1002.

7 illus, 11 ref

017897   Ramasamy V;Anandalakshmi K;Ponnusamy V (Physics Dep, Annamalai University, Annamalainagar-608 002, Tamil Nadu) : Rapid determination of quartz and structural characterisation of feldspar in rock using FTIR. Indian J Phys-Pt A 2003, 77(4), 347-52.

An infarared absorption method has been used to identify components (minerals) of rocks collected from various areas of Tamil Nadu without pre-treatments other than air drying and grinding and consequently with no significant modification of consitution that may occur with other conventional methods of examination requiring extensive pre-treatments. The results obtained from the IR absorption spectra show the presence of quartz, feldspars, gibbsite, illite, maghemite, magnetite, hematite, kaolinite, vermiculite and palygorskite minerals. The quality of the quartz mineral is substantiated by calculating the crystallinity index. The relative, vermiculite and quartz among the various sites are determined using extinction coefficient of the characteristic peak at 780 cm^-1. The quartz present in the samples from the site number 7 is in relatively well crystalline form than others. The presence of sanidine feldspars offers information on the temperature and pressure during the formation of rock resluting in Al/Si disorder.

3 illus, 3 tables, 21 ref

017896   Ramakrishnan S (Tata Institute of Fundamental Res, , Homi Bhabha Rd, Mumbai-400 005) : Novel charge density wave transition in crystals of R5Ir4Si10. Pramana J Phys 2002, 58(5-6), 827-37.

Review the observation of novel charge density wave (CDW) transitions in ternary R₅Ir₄Si₁₀ compounds. A high quality single crystal of Lu₅Ir₄Si₁₀ shows the formation of a commensurate CDW along c-axis below 80 K in the (h,O, l) plane that coexists with BCS type superconductivity below 3.9 K. However, in a single crystal of Er₅Ir₄Si₁₀, one observes the development of a 1D-incommensurate CDW at 155 K, which then locks into a purely commensurate state below 55 K. The well-localized Er³ moments are antiferromagnetically ordered below 2.8 K which results in the coexistence of strongly coupled CDW with local moment antiferromagnetism in Er₅Ir₄Si₁₀. Unlike conventional CDW systems, extremely sharp transition (width ~ 1.5 K) in all bulk properties along with huge heat capacity anomalies in these compounds makes this CDW transition an interesting one.

12 illus, 19 ref

017895   Rajarajan a K;Yusuf S M;Balaya P;Kulkarni R G (Solid State Physics Div, BARC, Bombay-400 085) : AC conductivity of mixed spinel NiAl 0.7Cr0.7Fe0.6O4. Pramana J Phys 2002, 58(5-6), 787-9.

AC Conductivity measurement are carried out across the metal to insulator transition in NiAl_0.7Cr_0.7Fe_0.6O₄. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. the exponent of the scaling behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime.

2 illus, 6 ref

017894   Raja Sudha G;Vimala Devi K;Arthi D; Subramanian S P;Srinivasan N;Saravanan R (Dep of Physics, Thiagarajar College, Madurai-625 009) : Experimetal ƒ′′ of As at 170, 200, 250 and 300 K from the Bijvoet pairs of GaAs. Bull Mater Sci 2002, 25(4), 325-7.

Anomalous dispersion effects lead to the modification of the measured X-ray structure factors. In this work, we have determined the imaginary part of the anomalous dispersion correction terms ƒ of arsenide atom (As), through the X-ray data collected using spherical single crystal of GaAs, at various temperatures, i.e. 170, 200, 250 and 300 K. It is stressed that more measurements of ƒ of the elements are needed to confirm the theoretical calculations.

5 tables, 7 ref

017893   Pushpa R;Narasimhan S (Theoretical Sciences Unit Dep, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, PO, Bangalore-560 064) : Double stripe reconstruction of the Pt(111) surface. Bull Mater Sci 2003, 26(1), 91-6.

Reconstruciton of the Pt(111) surface has been stndied theoretically, using a 2D generalization of the Frenkel-Kontorova model. The parameters in the model are obtained by performing ab initio density functional theory calculations. The Pt (111) surface does not reconstruct under normal conditions by experiments have shown that there are two ways to induce the reconstruction: by increasing the temperature, or by depositing adatoms on the surface. The basic motive of this reconstruction is a 'double stripe' with an increased surface density and alternating hcp and fcc domains, arranged to form a honeycomb pattern with a very large has been studied repeat distance of 100-330 A.The 'double stripe' reconstruction of the Pt(111) surface. In agreement with experiment, it has been found that it is favourable for the surface to reconstruct in the presence of adatoms, but not otherwise.

2 illus, 2 tables, 41 ref

017892   Pratap A;Lal R;Govind;Joshi S K (Theory Group, National Physical Laboratory, Dr K S Krishnan Road) : Spectral properties of doped bilayer cuprates at finite temperatures. Pramana J Phys 2002, 58(5-6), 855-9.

3 illus, 7 ref

017891   Prasad R;Benedek R;Thackeray M M (Physics Dep, Indian Institute of Technology, Kanpur-208 016) : Effect of Co on the magnetism and phase stability of lithiated manganese oxides. Bull Mater Sci 2003, 26(1), 147-50.

Fisrt-principles calculation of the relative energies of various phase of lithiate dmanganese oxides have been presented with and without Co. Ultrasoft pseudopotential method as implemented in the Vienna ab initio simulation package (VASP) has been used. The calculations employ the local spin density approximation (LSDA) as weel as the generalized gradient approximation (GGA). Monoclinic and rhombohedral structures in paramagnetic, ferromagnetic and antiferromagnetic (AF3) spin configurations. Spin polarization significantly lowers the total energy in all cases. The effect jof Co on the stability of these have been considered phases is discussed.

27 ref

017890   Prasad R (Physics Dep, Indian Institute of Technology, Kanpur-208 016) : Ground state structures and properties of small hydrogenated silicon clusters. Bull Mater Sci 2003, 26(1), 117-21.

Results for ground state structures and properties of small hydrogenated silicon clusters using the Car-Parrinello molecular dynamics with simulated annealing. The nature of bonding of hydrogen in these clusters. It has been found that hydrogen can form a bridge like Si-H-Si bond connecting tow silicon atoms. In the case of compact and closed silicon cluster hydrogen bonds to the silicon cluster from outside. To understand the structural evolutions and properties of silicon cluster due to hydrogenation. The cohesive energy and first excited electronic level gap of clusters have been died as a function of hydrogenation. That first excited electronic level gap of Si_n and Si_n H fluctuates as function of size and this may provide a first principle basis for the short-range potential fluctuations in hydrogenated amorphous silicon. The stability of hydrogenated silicon clusters is also discussed.

6 illus, 9 ref

017889   Prasad N (Biochemistry Dep, F B S and H, Rajendra Agricultural University, Pusa-848 125, Samastipur) : Excess free volumes and internal pressures of binary solutions of N, N-dimethylaniline and halomethanes. J pure appl Ultrasonics 2003, 25(1), 25-30.

Ultrasonic velocity, density and viscosity have been determined experimentally and free volume as well as internal pressure were computed for the binary mxtures of N, N-dimethylaniline with methylene chloride and chloroform. Excess values of viscosity, free volume and internal pressure were also deduced for these systems. The results have been discussed in the light of existing theories of molecular interaction involved and chemical constitution of the liquid components.

6 illus, 3 tables, 24 ref

017888   Petford Long A K;Portier X;Shang P;Larson D J (Materials Dep, , Parks Road, Oxford OX1 3PH, UK) : The development of information storage materials -How microscopy can help?. Pramana J Phys 2002, 58(5-6), 1125-9.

The response of giant magnetoresistance (GMR) devices depends critically on the films microstructure, with parameters such as layer thickness and interfacial abroptness being crucial. Presents results obtained using high resolution electron microscopy (HREM), chemical mapping and atom probe microanalysis. Local variations in the magnetic properters are induced by the microstructure and also when the films are patterned to form small elements. These lead to change in the magnetization reversal mechanism. Some results of the studies of the studies of the magnetization reversal carried out using in situ in Lorentz transmission electron microscopy (LTEM) magnetizing experiments are also included.

3 illus, 13 ref

017887   pattabiraman M;Rangarajan G;Kwang-Yong Choi; Lemmens P;Guentherodt G;Balakrishnan G;Paul D M K;Lees M R (Dep of Phys, Indian Institute of Tech, Chennai) : Polarized Raman scattering in single crystals of Nd 0.7Sr 0.3MnO 3. Pramana J Phys 2002, 58(5-6), 1013-17.

Reports polarized Raman scattering in single crystals of Nd_0.7Sr_0.3MnO₃. The temperature dependence of the MnO₆ octahedral bending and stretching models observed in the XX spectra points to the existence of local lattice distortions possibly polarons. The XY spectra have been analyzed using a collision-dominated model, which allows the extraction of the carrier scattering rate.

2 illus, 14 ref

017886   Pattabi M (Materials Sci Dep, Mangalore Univ, Mangalagangothri-574 199) : Insulator metal transition in a conservative system: an evidence for mobility coalescence in island silver films. Pramana J Phys 2002, 58(5-6), 1141-5.

Aging, which manifests itself as an irreversible increase in electrical resistance in island metal films is of considerable interest from both academic as well as applications point of view. aging is attributed to various causes, oxidation of islands and mobility of islands followed by coalescence (mobility coalescence) being the main contenders. The effect of parameters like substrate temperature, substrate cleaning, residual gases in the vacuum chamber, ultrasonic vibration of the substrate, suggest that the mobility coalescence is responsible for the aging in island metal films. Electron microscopy studies show evidence for mobility of islands at high substrate temperatures. The comparison of aging data of island silver films deposited on glass substrates in ultra high vacuum and high vacuum suggests that the oxidation of islands, as being responsible for aging in these films, can be ruled out. Further, under certain conditions of deposition, island silver films exhibit a dramatic and drastic fall in electrical resistance, making the insulator-metl transition. This interesting transition observed in a conservative system-after the stoppage of deposition of the film is a clear evidence for mobility coalescence of islands even at room temperature. The sudden fall in resistance is preceded by fluctuations in resistance with time and the fluctuations are attributed to the making and breaking of the percolation path in the film.

1 illus, 1 table, 12 ref

017885   Pandey R K;Harbola M K;Ranjan V;Singh V A (Physics Dep, Indian Institute of Technology, Kanpur-208 016) : Many electron effects in semiconductor quantum dots. Bull Mater Sci 2003, 26(1), 63-7.

Semiconductor quantum dots (QDs) exhibit shell structures, very similar to atoms. Termed as 'artificial atoms' by some, they are much larger (1-100 nm) than real atoms. One can study a variety of amny electorn effects in them, which are otherwise difficult to observe in a real atom. These effects have been treated within the local density approximation (LDA) and the Harbola-Sahni (HS) scheme. HS is free of the self interaction error of the LDA. Calculations have been performed in a three-dimensional quantum dot. A study of the size and shape dependence of the level spacing has been carried out. Scaling laws for the Hubbard 'U' are established.

6 illus, 1 tables, 10 ref

017884   Pandey N K;Padhan P;Budhani R C (Dep of Phys, Indian Institute of Tech, Kanpur-208 016) : Percolative transport in the vicinity of charge-order ferromagnetic transition in a hole-doped manganite. Pramana J Phys 2002, 58(5-6), 1075-8.

Reports measurements of non-linear charge transport in epitaxial (La_1-xPr_x)0.7Ca_0.3MnO₃ thin films fabricated on (100) oriented SrTiO₃ single crystals by pulsed laser deposition. the end members of this series, numely Pr_0.7Ca_0.3MnO₃ and La_0.7Ca_0.3MnO₃ are canonical charge-ordered (Co) and ferromagnetic manganites, respectively. The onset of the CO state in Pr_0.7Ca_0.3MnO₃ is manifested by a pronounced insulating behavior below ~ 200 K. The CO state remains stable even when a large (~ 2 x 10⁵ V/cm) electric field is applied across the thin film samples. However, on substitution of Pr with La, a crossover from the highly resistive CO state to a state of metallic character is observed at relatively low electric fields. The current-voltage characteristics of the samples at low temperatures show hysteretic and history dependent effects. The electric field driven charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ferromagnetic metallic clusters dispersed in a CO background.

2 illus, 5 ref

017883   Palkar V R;Pinto R (Tata Institut eof Fundamental Res, , Homi Bhabha Road, Mumbai-400 005) : BiFeO3 thin films: novel effects. Pramana J Phys 2002, 58(5-6), 1003-08.

Reports synthesis of phase-pure highly resistive magnetoelectric BiFeO₃ thin films on Pt/TiO₂/SiO₂/Si substrate by using pulsed laser deposition technique. For the first time saturated ferroelectric hysteresis loop has been observed. It has confirmed the presence of ferroelectricity in BiFeO₃ compound. The films exhibit dielectric anomaly near Neel temperature. This anomaly is related to the influence of vanishing magnetic order on the electric order. In situ domain alignment occurs during observation of the films under transmission electron microscope.

6 illus, 5 ref

017882   Pal D;Ramakrishnan S;Grover A K;Dasgupta D; Sharma B K (Tata Institute of fundamental Res, , Homi Bhabha Rd, Mumbai-400 005) : A study of the plasticity in the vertex matter across the second magnetization peak in a YBCO crystal via measurements of minor hysteresis loops. Pramana J Phys 2002, 58(5-6), 937-47.

Results of an investigation of the path dependence of the critical current density J_c due to the plastic deformation of the flux line lattice in a weakly pinned YBa₂Cu₃O₇-δ (YBCO) crystal for H c are reported. The procedure of minor hysteresis loops has been used to explore the path dependence of J_c and the metastability effects. Contrary to the behavior observed in low T_c systems, YBCO it is found at low temperatures, the multivaluedness in J_c(H) reaches its maximum value.

4 illus, 31 ref

017881   Pai S P;Wanchoo S;Purandare S C;Banerjee T; Apte P R;Narsale A M;Pinto R (Tata Instt of Foundamental Res, , Homi Bhabha Road, Mombai-400 005) : Self injection length in ... ferromagnet-superconductor multilayer thin films. Pramana J Phys 2002, 58(5-6), 1147-51.

Carries out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ 9LCMO) and YBa₂Cu₃O_1δ (YBCO) thin films. The hetero junctions were formed in situ by sequentially growing LCMO and YBCO films on (100) LaAlO_{3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μ, width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, Ic, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a Jc of ~ 2 x 10⁶ A/Cm², the LCMO side showed about half the value for the same thicknes (1800 Å and 1500 Å) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ~ 900 Å. To the authors' best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection.}

1 illus, 9 ref

017880   Nishihara Y;Kawanaka H;Bando H (Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan) : Local-moment formation and metal-nonmetal transition in Ca 1-x Y x VO 3 and Ca 1-x Y x TiO 3. Pramana J Phys 2002, 58(5-6), 737-42.

Electron-doped metallic states of Ca_1-xY_xVO₃ and Ca_1-xY_xTiO₃ change into non metallic states around x ~ 0.4 and 0.6 respectively. The residual resistivity in the metallic states increases with increasing effective magnetic moment or coefficient of T² term of resistivity. the effective moment reaches ~ 0.5 μB/molecule in Ca_1-xY_xVO₃ and also in Ca_1-xY_xTiO₃ near the metal-nonmetal phase boundary. In these metallic states, ~ 10% of 3d atoms seem to have large localized magnetic moments. In electron-doped metallic sample of Ca_1-xY_xVO₃, the temperature de pendence of resistance shows no resistance-minimum. However, weak negative magneto-resistance is observed for the sample with x = 0.2 up to 50 Tesla at 4.2 K.

4 illus, 14 ref

017879   Nirmala R;Sankaranarayanan V;Sethupathi K; Morozkin A V;Geethakumary T;Hariharan Y (Dep of Phys, Indian Inst of Tech, Chennai-600 036) : Electrical transport and magnetic ordering in. Pramana J Phys 2002, 58(5-6), 1101-1104.

New R₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.

3 illus, 1 table, 4 ref

017878   Niazi A;Paulose P L;Sampathkumaran E V; Rodewad U C;Jeitschko W (Tata Institute of Fundamental Res, , Homi Bhabha Road, Mumbai-400 005) : The growth of a single crystal of Sr e CuIrO 6 and its magnetic behavior compared to polycrystals. Pramana J Phys 2002, 58(5-6), 1069-73.

Grows single crystals of the psuedo-one-dimensional compound Sr₃CuIrO₆, a K₄CdCl₆-derived monoclinic structure with Cu-Ir chains along the [101] direction. Presents the ac and dc magnetization behavior of the single crystals in comparison with that of the polycrystalline from reported earlier. There is a distinct evidence for at least two magnetic transitions, at 5 K (t₁) and 19 K (T₂), with different relative magnitudes in the single and polycrystals. The low temperature magnetic relaxation behavior of both the forms is found to be widely different, exhibiting unexpected time dependence.

2 illus, 5 ref

017877   Nguyen-Manh D;Saha-Dasgupta T;Andersen A K (Materials Dep, University of Oxford, Parks Road, Oxford OX1 3PH, UK) : Tight-binding model for carbon from the third-generation LMTO method: a study of transferability. Bull Mater Sci 2003, 26(1), 27-32.

The third-generation LMTO method provides a new wave function basis set in which the energy dependence of the interstitial region and inside muffin-tin (MT) spheres is treated on an equal footing. Within the improved method, basis functions in the interstitial are the screened spherical waves (SSWs) with boundary condition defined in terms of a set of 'hadr' sphere radii a_RL. Energy eigenvalues obtained from the single-particle Schrodinger equation for MT potential is energetically accurate and very useful for predicting a reliable first-principles tight-binding (TB) model of widely different systems. A possibility of the new basis sets transfereability to different environment which could be crucial for TB applications investigated to very large and complicated systems in realistic materials modelling. For the case of C where the issue of sp² vs sp³ bonding description is primarily important, it has been found that by downfolding the unwanted channels in the basis, the TB electronic structure calculations in both hexagonal graphite and diamond structures are well compared with those obtained form the full LDA schemes if the same choice of hard sphere radii, a_RL and a fixed, arbitrary energy, ε_v are used. Moreover, the choice is robust and transferable to various situations, from different forms of graphite to a wide range of coordination. Using the obtained minimal basis set, the TB Hamiltonian and overlap matrices for different structure types for carbon were investigated in particular, the on-site and hopping parameters (Y₁, Y₂..., Y₆) within an orthogonal representation for Slonczewski-Weiss-McClure (SWMcC) model of the Bernal structure. Theoretical values are in excellent agreement with experimental ones from magnetoreflection measurements of Fermi surfaces for hexagonal graphite.

6 illus, 1 tables, 19 ref

017876   Nguyen-Manh D;Pettifor D G;Cockayne D J H; Mrovec M;Znam S;Vitek V (Materials Dep, Univeristy of Oxford, Parks Road, Oxford OX1 3PH, UK) : Environmentally dependent bond-order potentials: new developments and applications. Bull Mater Sci 2003, 26(1), 43-51.

The bond-order potentials (BOPs) idea employs the orthogonal two-centre tight-binding (TB) representation for the bond energy and the Harris-Foulkes approximation for the repulsive pairwise contribution. In the last ten years, although many efforts have been focused on theoretical calculations of the bond order expression, the BOPs still suffers from the uncertainty of how best to choose the semi-empirical TB parameters that enter the scheme. Recent developments to obtain the reliable and transferable BOPs which help to extent the accuracy and applicability to technologically important multicomponent systems. It has been found that a simple pair potential is unsuitable for describing the environmental screening effects due to the s and p orbital overlap repulsion in strong covalent systems. By adding the environmental dependent repulsive term, teh Cauchy pressure problem has been removed and it has been possible to get the BOPs for studying dislocations, extended defects and mechanical properties of high temperature intermetallic Ti-Al alloys. The first derivation of explicit analytic expressions for environmental dependence of σ, θ and δ bond intergrals has been presented by inverting the non-orthogonal matrix. A new environmentally depedent BOPs has been developed for bcc-Mo indicating that the ment with recent ab initio calculations

7 illus, 2 tables, 37 ref

017875   Narasimhan S;De Gironcoli S (Theoretical Sciences Unit Dep, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur PO, Bnagalore-560 064) : Exchange-correlation errors at harmonic and anharmonic orders: the case of bulk Cu. Bull Mater Sci 2003, 26(1), 75-8.

As an aid towards improving the treatment of exchange and correlation effectes in electronic structure calculations, it is desirable to have a clear picture of the errors intorduced by currently popular approximate exchange-correlation functionals. Ab initio density functional theory and density functionaly perturbation theory calculations have been performed to investigate the thermal propterties of bulk Cu, using both the local density approximation (LDA) and the generalized gradient approximation (GGA). Thermal effects are treated within the quasiharmonic approximation. The LDA and GGA errors for anharmonic quantities are an order of magnitude smaller than for harmonic quantities. This might be a general feature. Much closer agreement with experiment than earlier, more approximate calculations has been obtained.

3 illus, 19 ref

017874   Murugan P;Pothiraj R;Ray S D D;Ramachandran K (School of Physics, Madurai Kamaraj University, Madurai-625 021) : Si diffusion in GaAs. Bull Mater Sci 2002, 25(4), 335-40.

Theoretical studies are carried out to ascertain the dominant mechanism of Si diffusion in GaAs. Lattice dynamical model calculations have shown that the most probable diffusion mechanism is through a single vacancy even though several experiments cannot fix the mechanism as substitutional, substitutional interstitial pair or neutral defect pair.

3 illus, 4 tables, 23 ref

017873   Mookerjee A;Saha-Dasgupta T;Dasgupta I;Arya A;Banerjee S;Das G P (NO, S.N. Bose National Centre for Basic Sciences, JD-Block, Sector-III, Salt Lake, Kolkata-700098) : A first-principles thermodynamic approach to ordering in binary alloys. Bull Mater Sci 2003, 26(1), 79-89.

The communication reviews the augmented space based approaches to thermodynamics and ordering of binary alloys. Several examples of metallic alloys have been given as illustrations to illustrate methodology.

11 illus, 25 ref

017872   Modak P;Rao R S;Godwal B K;Sikka S K (High Pressure Physics Div, BARC, Mumbai-400 085) : Electronic structure of MgB2. Pramana J Phys 2002, 58(5-6), 881-4.

Results of ab intio electronic structure calculations on the compound MgB₂ using the FPLAPW method employing GGA for the exchange-correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, c/a ratio and bulk modulus, all of which are in excellent agreement with experiment. Obtains the mass enhancement parameter by using calculated D(E_F) and the experimental specific heat data. The Tc is found to be 24.7 K.

3 illus, 7 ref

017871   Miah M M H;Islam M N;Faruque M R I (Physics Dep, University of Chittagong, Chittagong-4331, Bangladesh) : Calculation of neutron cross section for <. Indian J Phys-Pt A 2003, 77(4), 383-6.

Neutron total cross sections and differetial elastic scattering cross sections for the nuclides ⁹⁰Zr, ²⁰⁸Pb and ²⁰⁹Bi were calculated using different global optical potential (SOP) parameter sets at neutron energies form 0.5-25 MeV. Calculated cross sections for the corresponding nuclides were compared with their experimental data obtained by the EXFOR file to select the best fit parameter sets. It is found that the parameter sets fof Ferer Rapaport for ⁹⁰Zr, and Bechetti and Greenless for ²⁰⁸, and ²⁰⁹Bi are the best fitted set to obtain experimental data of total cross sections and angular distributions of these nuclides.

6 illus, 1 tables, 14 ref

017870   Mhatre U R;singh S K;Kothari d C;Nagarajan R; (Dep of Phys, Univ of Mumbai, Vidyanagari, Mumbai-400 098) : Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation. Pramana J Phys 2002, 58(5-6), 1093-1100.

Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional changes in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy as measured using Mossbauer spectroscopy of virgin and irradiated Fe₄₀Ni_{40B20 and Fe40Ni38Mo4B18 metallic glass ribbons. 90 MeV ¹²⁷ I beam was used for the irradiations. Irradiation doses were 5 x 10¹³ and 7.5 x 10¹³ ions/cm². The relative intensity ration D23}

4 illus, 3 tables, 19 ref

017869   Meyyappan M;Sethupathy P (Physics Dep, Alagappa Goverment Arts College, Karaikudi-630 003) : Theoretical evaluation and experimental verification of ultrasonic velocity in binary liquid mixtures. J pure appl Ultrasonics 2003, 25(1), 1-5.

The ultrasonic velocity and adiabatic compressibility measurements at 2MHz, at room temperature 303 K in mixtures of m-toluidine + CCI₄ and m-tluidine + O-Chlorophenol have been used to study the acoustical behaviour of these liquids and liquid mixtures. By extending the Rao's rule to binary liquid mixtures at constant pressure and temperature, three new formulae have been predicted for the determination of ultrasomic velocity and compressibility in binary liquid mixtures. Its uitlity for the suitability is verified with the corresponding values calculated with the other formulae.

2 tables, 30 ref

017868   Mathe V L;Patankar K K;Lotke S D;Joshi P B; Patil S A (Dep of Physics, Shivaji University, Kolhapur-416 004) : Structural, dielectric and transport properties of Pb(Mn_0.5W_0.5)O₃. Bull Mater Sci 2002, 25(4), 347-50.

Polycrystalline Pb(Mn_0.5W_0.5)O₃, a ferroelectric oxide having perovskite structure, was prepared by high temperature solid state reaction technique. Preliminary X-ray diffraction analysis confirms single phase formation with the lattice parameters a=7.2501 A, b=8.1276 A and c=12.0232 A. Room temperature dielectric constant (ε) and loss tangent (tan δ were scanned with respect to frequency in the range 100 Hz-1 MHz. Detailed study of dielectric constant and electrical conductivity reveals a phase change around 400 K, which is quite different from those in the other materials of the same type. Further, the seeback coefficient (α is temperature independent. The condition is interpreted as due to small polaron hopping.

6 illus, 16 ref