017867   Mathe V L;Patankar K K;Kothale M B;Kulkarni S B;Joshi P B;Patil S A (Dep of Phys, Shivaji Univ, Kolhapur-416 004) : Preparation, structural analysis and dielectric properties. Pramana J Phys 2002, 58(5-6), 1105-13.

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycriystalline samples of Bi_xLa_1-xFeO₃ (x=0,0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. the single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0,0.2,0.4,0.6 are found to be orthorhombic while the sample with x = 0.8 is triclinic. The dielectric constant (ε') and dissipation factor (tanδ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. the dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Neel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε' are found to be maximum for the sample x = 0.2 at room temperature.

7 illus, 1 table, 8 ref

017866   Marchetti P A;Su Z B;Yu L (NO, , ) : Metal insulator crossover in high Tc cuprates: a gauge field approach. Pramana J Phys 2002, 58(5-6), 803-08.

A metal-inslatoc crossover appears in the experimental data for in-plane resistivity of underdoped cuprates and a range of superconducting cuprates in the presence of a strong magnetic field suppressing superconductivity. Proposes an explanation for this phenomenon based on a gauge field theory approach to the t-J model. In this approach, based on a formal spin-charge separation, the low energy effective action describes gapful spinous (with a theoretically derived doping dependence of the gam M²_s~ δ<124>Inδ<124> ) and holons with finite Fermi surfae (εF~tδ) interacting via a gauge field whose basic effect on the spinons is to bind them into overdamped spin waves, shifting their gap by a damping term linear in T, which causes the metal-insulator crossover. The presence of a magnetic field perpendicular to the plane acts by increasing the dampling, in turn producing a big positive transverse in-plane magnetoresistance at low T, as experimentally observed.

2 illus, 12 ref

017865   Mansour N A;Diab A M (Physics Dep, Faculty of Science, Zagazig University, Zagazing, Egypt) : Phenomenological anharmonic vibrational model description for the ground state band energy of even-even nuclei. Indian J Phys-Pt A 2003, 77(4), 377-81.

The results from the cubic polynomial (CP) formula of the square of the angular velocity and the nuclear momemts of inertia are compared with those from the variable moment of inertia (VMI) model and the available experimental information on transition energies for yrast line in even-even nuclei. The evaluated model parameters lead to an excellent fit for all energy levels (I-24). The calculated critical spin for backbending in the ℑ-@² plot is found to be in agreement with the experimental data.

2 illus, 6 tables, 18 ref

017864   Majumdar S;Sampathkumaran E V;Berger S T; Della Mea M;Michor H;Bauer E;Brando M;Hemberger J;Loidl A (Tata Institute of Fundamental Research, , Homi Bhabha Road) : Spin-glass, antiferromagnetism and kondo behavior in Ce2Au1-x Cox Si3 alloys. Pramana J Phys 2002, 58(5-6), 777-82.

Recently, the solid solution Ce₂Au_1-xCo_xSi₃ has been shown to exhibit many magnetic anomalies associated with the competition between magnetic ordering and the Kondo effect. Reports high pressure electrical resistivity of Ce₂AuSi₃, as susceptibility (X) and magnetroesistance of various alloys of this solid solution in order to gain better knowledge of the magnetism of these alloys. High pressure resistivity behavior is consisten with the proposal that Ce₂auSi₃ lies at the left-hand side of the maximum in doniach's magnetic phase diagram. The ac X data reveal that there are in fact two magnetic transitions, one at 2 K and the other at 3 K for this compound, both of which are spin-glass-like. However, as the Co concentration is increased, antiferromagnetism is stabilized for intermediate compositions before attaining non-magnetism for the Co end member.

3 illus, 6 ref

017863   Mahajan R P;Patankar K K;Kothale M B; Chaudhari S C;Mathe V l;Patil S A (Dep of Phys, Shivaji Univ, Kolhapur-416 004) : Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties. Pramana J Phys 2002, 58(5-6), 1115-24.

CoFe₂O₄-BaTiO₃ composities were prepared using conventional ceramic double sintering process with various compositions. Presence of two phase in the composities was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ε') with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ε') and low tangent (tan δ. The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.

8 illus, 1 tables, 15 ref

017862   Lohneysen H;Pfleiderer C;Schroder A;Stockert O (Physikalisches Institut, Universitat Karlsruhe, D-76128 Karlsruhe, Germany) : Metals near a magnetic instability. Pramana J Phys 2002, 58(5-6), 743-54.

Zero-temperature magnetic phase transitions exhibit an abundance of nearly critical magnetic fluctuations that allow to probe the traditional concepts of the metallic state. For the prototypical heavy-fermion compound, CeCuAu_x, a breakdown of the Fermi-liquid properties may be tuned by au concentration, hydrostatic pressure, or magnetic field. The d-electron weak itinerant feromagnet ZrZn₂, on the other hand, was recently found to display superconductivity in coexistence with ferromagnetism

8 illus, 40 ref

017861   Levett S J;Dewhurst C D;Paul D M K (Dep of Phys, Univ of Warwick, Coventry CV4 7AL, UK) : Vortex lattice transitions in YNi2B2C. Pramana J Phys 2002, 58(5-6), 913-17.

Performes extensive small-angle neutron scattering (SANS) diffraction studies of the vertex lattice in single crystal YNi₂B₂C for B c. High-resolution SANS, combined with a field-oscillation vertex lattice preparation technique, allows to separate Bragg scattered intensities from two orthogonal domains and accurately determine the unit cell angle, β. The data suggest that upon increasig field there is a finite transtion width where both low- and high-field distored hexagonal vortex lattice phases, mutually rotated by 45°C, coexist. The smooth variation of diffracted intensity from each phase through the transition corresponds to a redistribution of population between the two types of domains.

4 illus, 7 ref

017860   Lal T;Harish Kumar;Singhal R P;Saxena A K;Rao S U M (NO, National Physical Laboratory, Dr. K S Krishnan Marg, New Delhi - 110 012) : Interlaboratory proficiency testing: mass measurement - 2001/02. MAPAN 2003, 18(2), 103-14.

Under NPL-NABL Proficiency Testing Program, an inter-laboratory comparison on the calibration of a set of four standard masess of nominal values of 1g, 10g, 200g and 1000g and fifth "non-standard" mass of 124g has been carried out amongst the eight NABL accredited calibration labratoreis including Regional Reference Standard Laboratories of the Department of Legal Metrology, Government of India. The purpose was to assess and establish the technical competence of these laboratories as per the NABL and APLAC requirements. NPL coordinated the intercomparison and acted as the reference laboratory. The program was started in Feburary 2001 and completed during NOvember 2001. Reports the measurement results of the participating laboratories and their respective En values. Only two laboratories were found to be performing well.

2 illus, 4 tables, 10 ref

017859   Lakshmi N;Pandey A;Venugopalan K (Dep of Physics, Mohanlal Sukhadia University, Udaipur-313 001) : Hyperfine field distributions in disordered Mn₂CoSn and Mn₂NiSn Heusler alloys. Bull Mater Sci 2002, 25(4), 309-13.

Heusler alloys, Mn₂CoSn and Mn₂NiSn, were perpared and characterized by X-ray studies. Mossbauer studies using Sn-119 were carried out to investigate the hyperfine fields present at the Sn site in these alloys. The hyperfine field distribution in these alloys as well as X-ray studies point to the chemical disorder present in both days. Co-exestence of a paramagnetic portion along with the magnetic hyperfine part was observed in Mn₂CoSn even at low temperatures, while this was not found in Mn₂NiSn spectra. Hyperfine fields at Sn site were calculated using Blandin and Campbell model and compared with the experimental results.

4 illus, 3 tables, 14 ref

017858   Lakshmi L S;Sridharan V;Natarajan D V;Sastry V S;Radhakrishnan T S (Materials Sci Div, Indira gandhi Centre for Atomic Res, Kalpakkam-603 102) : Mn sit substituteion of La 0.67 Ca 0.33 MnO 3 with close shell ions: effect on magnetic transition temperature. Pramana J Phys 2002, 58(5-6), 1019-26.

Mn site is substituted with close shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at . Substitution did not change either the crystal symmetry or the oxygen stroichiometry. all substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (T_p(ρ) and T_C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii between the substitutent (rM) and the Mn³⁺ ion (r_Mn³⁺) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.

4 illus, 1 table, 24 ref

017857   Kuriakose S;Vijayan K K;Eapen S M;Shaji S; Nair K P R;Rasheed T M A (Laser and Spectroscopy Lab, Dep of Physics, University of Science and Technology, Cochin-682 022) : Overtone spectrum of formamide in the near infrared region - evidence for the inhibition of lone pair trans effect. Asian J Spectrosc 2002, 6(1), 43-6.

The near infrared overtone absorption spectrum of liquid phase formamide is reported. The analysis of the observed CH local mode mechanical frequency value shows that the lone pair trans effect is inhibited in formamide.

4 illus, 1 table, 15 ref

017856   Kupfer H;Ravikumar G;Wolf T H;Zhukov A A;Wuhl H (NO, , ) : Commensurability oscillations in NdBa2Cu3O y single crystals. Pramana J Phys 2002, 58(5-6), 919-24.

Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization in very pure twinned and twin-free NdBa₂Cu₃O_y single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within the unit cell and idscussed with respect to temperature, field, anisotropy, and twin structure.

3 illus, 11 ref

017855   Kundaliya D C;Vij R;Tulapurkar A A;Vaidya U; Pinto R;Kulkarni R G (Dep of Phys, Saurashtra Univ, Rajkot-360 005) : Temperature hysteretic effect and its influence on colossal magnetoresistance of La. Pramana J Phys 2002, 58(5-6), 1041-4.

Electrical resistante (R) measurement of a bulk La_0.33Nd_0.33Ca_0.33MnO₃ perovskite in magnetic fields up to 40 KOe have revealed anomalous temperature hysteretic effects both in 0 Oe and 20 kOe magnetic fields. The sharp peak observed in the R vs. T plot indicates the occurrence of metal-to-insulator (M-I) transition at a temperature of T_MI=110 K and 140 K, for cooling and warming paths, respectively, An applied magnetic fields of 20 kOe reduce the resistance and shifts T_MI to 160 K and 185 k for cooling and warming, respectively. Observes a much higher resistance in the cooling path than in the warming path leading to the hysteretic resistance ratio (R_cool/R_warm) of 200 at 110 K and 1.8 at 160 K for O Oe and 20 kOe, respectively. Record values of colosal magnetoresistance (CMR) have been achieved. The CMR value reaches nearly 99% in the temperature ranges of 90 K to 140 K and 90 K to 170 K for 20 kOe and 40 kOe magnete fields in the cooling mode, respectively. The observed unusual behavior is attributed to the co-existence of La-rich and Nd-rich domains assmed to be distributed randomly in the compound.

3 illus, 4 ref

017854   Kundaliya D C;Tulapurkar A A;John J;Pinto R; Kulkarni R G (Dep of Phys, Saurashtra Univ, Rajkot-360 005) : Enhanced temperature-independent magnetoresistance below the metal-insulator transition temperature of epitaxial. Pramana J Phys 2002, 58(5-6), 1089-92.

Epitaxial La_0.2Nd_0.4Ca_0.4MnO_{3 thin films have been deposited at 800°C on LaAlO3 substrate using pulsed laser deposition technique. The structural and magnetotransport properties of the films have been studied. The sharp peak in the temperature dependence of the resistance corresponding to metal-to-insulator transition (Tp has been observed at a temperature of Tp = 82 K, 97 K and 110 K for 0 Oe, 20 kOe and 40 kOe magnetic fields, respectively. The film exhibits a large nearly temperature-independent magnetoresistance around 99% in the temperature regime below Tp.}

2 illus, 8 ref

017853   Kumar S;Auluck S (Physics Dep, Institute of Engineering and Technology M.J.P. Rohilkhand University, Bareilly-243 006) : Electronic structure and optical properties of thorium monopnictides. Bull Mater Sci 2003, 26(1), 165-8.

Calculates the electronic density of states (DOS) and dielectirc function have been calculated for the ThX (X=P, As and Sb) using the linear muffin tin orbital method within atomic sphere approximation (LMTOASA) including the combined correction terms. The calculated electronic DOS fo ThSb has been compared with the available expermental data and it has been found to be a good agreement. The calculated optical conductivity for ThP and ThAs is increasing monotonically, while for ThSb a sharp peak has been found at 6.5 eV.

5 illus, 19 ref

017852   Krishnamurthy V V;Suzuki M;Kawamura N; Ishikawa T (RIKEN Harima Institute, , SPring8, 1-1-1 Kouto, Mikazuki, Sayo, Hyogo-697-5148, Japan) : X-ray magnetic circular dichroism at IrL 2, 3 edges in Fe 100-x Ir x and Co100-x Ir x alloys: Magnetism of 5d electronic states. Pramana J Phys 2002, 58(5-6), 761-7.

The formation induced 5d magnetic moment on Ir in Fe_100-xIr_x (x=3,10 and 17) and Co_100-xIr_x (x=5,16,25 and 32) alloys has been investigated by X-ray magnetic circular dichroism (XMCD) at Ir L_2,3 absorption edges. Sum rule analysis of the XMCD data show that the orbital moment of Ir is in the range of -0.071(2)μB to -0.030(1)μB in Fe-Ir alloys and -0.067(2)μB to 0.024(1) μB in co-Ir alloys. Finds that the total moment of Ir in Fe-Ir alloys is approximately 1/5 of the total 3d moment on Fe at all the three compositions. In contrast, the total moment on Ir in Co-Ir alloys varies between 1/6 to 1/16 of the 3d moment on cobalt. The observed trends of Ir moments and the role of interatomic exchange interaction in 5d moment formation are discussed.

2 illus, 2 tables, 16 ref

017851   Kothawale R R;Dole B N;Shah S S (Dep of Phys, Shri Shivaji college, Barshi, Solapur-413 411) : Effect of substitution of Ce on superconducting properties of Bi 1-7 Pb0.3 Sr 2 Ca 2-x Ce x Cu3 O10 + system. Pramana J Phys 2002, 58(5-6), 871-5.

Investigates the superconducting properties of the Bi_1.7Pb_0.3Sr₂Ca_2-xCe_xCu₃O₁₀₊ δ system with x = 0.00, 0.02, 0.04, 0.08 and 0.1 by X-ray diffraction and magnetic susceptibility. the substitution of Ce for Ca has been found to drastically change the superconducting properties of the system. X-ray diffraction studies on these compounds indicate decrease in the c-parameter with increased substituteion of Ce at ca site and volume fraction of high Tc (2:2:2:3) phase decreases and low Tc phase increases. The magnetic susceptibility of this compound shows that the diamagnetic on set superconducting transition temperature (onset) varies from 109 K to 51 K for x = 0.000, 0.02, 0.04, 0.08 and 0.1. These results suggest the possible existence of Ce in a tetravalent state rather than a trivalent state in this system; that is, Ca²⁺ → Ce⁴⁺ replacement changes the hole carrier concentration. Hole filling is the cause of lowering tc of the system.

2 illus, 3 tables, 13 ref

017850   Kohara T (Dep of Material Sci, Himeji Inst of Tech, Kamigori, Akogun, Hyogo 678-1297, Japan) : New aspects of URu2 Si2 and CeTIn5 (T=Rh, Ir, Co) observed by high pressure NMR and NQR. Pramana J Phys 2002, 58(5-6), 755-60.

NMR and NQR studies on two interesting system (URu₂Si₂, CeTIn₅) were performed under high pressure. (1) URu₂Si₂: In the pressure range 3.0 to 8.3 kbar, observes new ²⁹Si NMR signals arising from the antiferromagnetic (AF) region besides the previously observed ²⁹Si NMR signals which ocme from the paramagnetic (PM) region in the sample. This gives definite evidence for spatially-inhomogeneous development of AF ordering below To of 17.5 K. The volume fraction is enhanced by applied pressure, whereas the value of internal field (~91 mT) remains constant up to 8.3 kbar. In the AF region, the ordered moment is about one order or magnitude larger that 0.03 μB. (2) CeTIn_{5: The pressure and temperature (T) dependences of nuclear spin-lattice relaxation rate 1/T1 of ¹¹⁵In in CeTIn5 have shown that the superconductivity (SC) occurs close to an AF instability. From the T dependences of 1/T1 and Knight shift below Tc, CeTIn5 has been found to exhibit non-s wave (probable d wave) SC with even parity and line nodes in the SC energy gap.}

4 illus, 9 ref

017849   Khare N;Gupta A K;Moharil U P;Raychaudhuri A K;Pai S P;Pinto R (National Physical Laboratory, , Dr.K S Krishnan Road, New Delhi-110 012) : Study of magnetoresistance and conductance of bicrystal grain boundary in La_0.67Ba_0.33MnO₃ thin film. Pramana J Phys 2002, 58(5-6), 1165-70.

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7° SrTiO₃ bicrysal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T<62>K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is non-linear. analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<60> 175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperature (T<62> 175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.

4 illus, 18 ref

017848   Kataria N D;Misra M;Pinto R (Superconductivity Div, National Physical Laboratory, New Delhi-110 012) : Sensitivity of surface resistance measurement of HTS thin films by cavity resonator, dielectric resonator and microstrip line resonator. Pramana J Phys 2002, 58(5-6), 1171-7.

Microwave surface resistance (R_s) of silver-doped YBa₂Cu₃O_7-δ (YBCO) thin film, deposited by laser ablation technique on 10 mm x 10 mm LaAlO₃ substrate, has been measured by resonant techniques in the frequency range from 5 GHz to 20 GHz. The geometrical factor of the sample and the resonator has been determined theoretically by the knowledge of the electromagnetic field distribution in the resonators. The microwae surface resistance of the superconducting sample is then extracted from the measured Q value as a function of temperature. The sensitivity of the R_s measurement, that is, the relative change in the Q value with the change in the R_s value is determined for each resonator.

4 illus, 4 ref

017847   Kataria N D;Daya K S;Das V G (NO, National Physical Laboratory, New Delhi-110 012) : Analysis of shielded TE 011 mode composite dielectric resonator for stable frequency reference. Pramana J Phys 2002, 58(5-6), 1203-06.

Analysis of a TE₀₁₁ mode composite sapphire-rutile dielectric resonator has been carried out to study the temperature variation of resonance frequency, close to the Cs atomic clock hyperfine frequency of 9.192 GHz. The complementary behavior of dielectric permittivity with temperature of the composite has been exploited to obtain the desired turning point in the resonant frequency. The frequency of the composite structure is found to be independent of the shield diameter beyond four times the puck diameter.

4 illus, 3 ref

017846   Karan S;Sen Gupta S P (Materials Science Dep, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700 032) : Growth and microhardness studies in solution-grown single crystal of thenardite. Indian J Phys-Pt A 2003, 77(4), 327-32.

Single crystals of Thenardite (Sodium Sulphate Na₂SO₄) were grown by slow evaporation technique at room temperature. Mechanical characterization was done by Vickers microhardness testing. Load varying form 10 to 120 g was aplied on selected (011) faces over a fixed interval of 10 seconds. Vickers hardness number (H_v) were found to decrease with increase in load. Meyer index 'n' was found to be less than 2 as expected and thus the particular crystal system belongs to soft material category. Neither Kich's law nor Hays and Kendall's law can satisfactorily explain the nonlinear variation of microhardness with load. Instead, it was best explained by Li and Bradt's Proportional Specimen Resistance (PSR) model. Crack lengths were measured and found to increase with load. The fracture toughness values (K_c) were estimated to be 0.227 and 0.151 MNm^-3/2 for (011) faces at 100 and 120 g respectively. The Brittleness indices (B_i) were determined as 1.455 and 3.297 mm^-1/2 respectively for the same faces at the same faces loads. Using Wooster's empirical relation, elastic stiffness coefficient, c₁₁ has been calculated from hardness data.

7 illus, 2 tables, 32 ref

017845   Kar M;Ravi S (Dep of Phys, Indian Institute of Tech, Guwahati-781 039) : Metal-insulator transition in electron-doped Ba 1-x La x MnO 3 compounds. Pramana J Phys 2002, 58(5-6), 1009-12.

Electron-doped (Ba_1-xLa_x)MnO₃ compounds were prepared for x = 0-0.5. Measurements of X-ray diffraction (XRD) at room temperature and temperature variation of dc electrical resistivity down to 20 K were carried out. samples with x=0.2-0.5 exhibit meal-insulator (M-I) transition. The maximum M-I transition temperature (T_c) of 289 K was observed for 30% of La doping (x=0.3). XRD patterns of these samples (x=0.2-0.5) were analyzed using Rietvel refinement. These samples are found to be mostly in single-phase from with orthorhombic symmetry (space group Pbnm). Finds strong correlation between Mn-O-Mn bond angles and T_c of M-I transition. The resistivity data below T_c could be fitted to the expression ρ=ρ2T² and this show that double exchange interaction plays a major role even in Mn⁴⁺ -rich compound. Above T_c the resistivity data were fitted to variable range hopping and small polaron models.

2 illus, 1 table, 9 ref

017844   Kamlesh Kumari;Singhal R K;Garg K B;Heinonen M;Leiro J;Gupta A;Agarwal S K (Physics Dep, Condensed Matter Physics Laboratory, University of Rajasthan, Jaipur-302 004, Rajasthan) : Photoemission study of Ba 2+ and Nd 3+ substitution for Ca 2+ in the BSCCO (2212) superconducting system. Indian J Phys-Pt A 2003, 77(4), 333-9.

The photoemission measurements have been carried out on the BSCCO (2212) superconducting system to understand the effect of substitution of trivalent impurity (Nd) for divalent Ca and the effect of substitution Ba that has a larger ionic radius than Ca. The two compounds have been characterized by XRD and resistivity measurements. The photoemission have been made on the Bi 4f, Sr 3d and Ca 2p core lelvels. The core level spectra show some changes-their binding energies and fine structure - due to subsitution in the two cases - which have been discussed in detail.

9 illus, 2 tables, 20 ref

017843   Jayagopal Uchil (Materials Science Dep, Mangalore Univ, Mangalagangothri-574 199) : Shape memory alloys - characterization techniques. Pramana J Phys 2002, 58(5-6), 1131-9.

Shape memory alloys are the generic class of alloys that show both thermal and mechanical memory. The basic physics involved in the shape memory effect is the reversible thermoelastic martensitic transformation. In general, there exists two phases in shape memory alloys, viz. a high temperature phase or austenitics phase (A) and a low-temperature phase or martensitic phase (M). In addition, an intermediate R phase exists in some special cases. The M↔A transformation is associated with a recoverable strain of about 6.5-8% and the R↔A transformation is associated with a recoverable strain of about 1%. The former transformation has been widely used in the applications like antenna deployment of satellite, aerospace couplings, orthodontic arch wires, medical guide wires for diagnostic and therapeutic catheters and other industrial applications. Our group has been giving emphasis to the characterization techniques for R phase, using differential scanning calorimetry (DSC), electrical resistivity probe (ER) and thermomechanical analyzer (TMA). R phase is found to have attractive features like stability against thermal cycling, a small thermal hysteresis and a negligible strain recovery fatigue. DSC has been used successfully to characterize the recoverable strain parameters, apart from the determination of transformation temperatures. ER is used, for the systematic study of the dependence of various phases on heat-treatment temperatures.

3 illuse, 1 table, 15 ref

017842   Janawadkar M P;Baskaran R;Nagendran R; Gireesan K;Hrishkumar N;Saha R;Vaidhyanathan L S;Jayapandian J; Hariharan Y;Radhakrishnan T S (Materials Sci Div, Indira Gandhi Centre for Atomic Res, Kalpakkam-603 102) : SQUID-based measuring systems. Pramana J Phys 2002, 58(5-6), 1159-64.

Program has been developed and initiated at the Indira Gandhi Centre for atomic Research (IGCAR) for the utilization of SQUID sensors in various application areas. DS SQUID sensors based on Nb-AlO_x-Nb Josephson junctions have been designed and developed inhouse along was associated flux-locked loop (FLL) electronics. a compact low field SQUID magnetometer in sertible in a liquid helium storage dewar has also been developed inhouse and is in use. Effort to build a high field SQUID magnetometer, SQUID-DAC system, are in progress. A planar gradiometric DC SQUID sensor for non-destructive evaluation (NDE) application to be used in relatively unshielded environment has been designed and developed. An easily portable NDE cryostat with a small lift-off distance, to be used in external locations has been designed and tested. The magnetic field produced by a given two-dimensional current density distribution is inverted using the Fourier transform technique.

2 illus, 6 ref

017841   Husain S;Choudhary R J;Ravi Kumar;Patil S I; Srivastava J P (Dep of Phys, Aligarh Muslim Univ, Aligarh-202 002) : Study of structural and electronic transport properties of Ce-doped LaMnOe. Pramana J Phys 2002, 58(5-6), 1045-9.

The structural and electronic transport properties of La_1-xCe_xMnO₃ (x=0.0-1.0) have been studied. all the samples exhibit orthorhombic crystal symmetry and the unit cell volume decrease with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.

2 illus, 1 table, 6 ref

017840   Harbola M K;Sen K D (Physics Dep, Indian Institute of Technology, Kanpur-208 016) : Obtaninig kohn-sham potential without taking the functional derivative. Bull Mater Sci 2003, 26(1), 69-74.

Over the past decade and a half, many new accurate density functionals, based on the generalized gradient approximation, have been proposed, and they give energies close to chemical accuracy. However, accuracy of the energy functional does not guarante that its functional derivative, which gives the correspoding potential, is also accurate all over space. For example, although the Becke88 exchange-energy functional gives very good exchange energies, its functional derivative goes as -1/2 in comparison to the correct -1/r for r->-∞ , where r is the distance of the electron from a finite system. On the other hand, accuracy of the potential is of prime importance if one is interested in properties other than the total energy; properties such as optical response depend crucially on the potential in the outer regions of a system. A different approach has been presented based on the ideas of Harbola and Sahni, to obtain the potential directly from the energy desnsity of a given approximation, without taking recourse to the functional derivative route. This leads to a potential that is as accurate as the functional itself. The accuracy of the approach has been demonstrated by presenting some results obtained from the Becke88 functional.

1 illus, 2 tables, 29 ref

017839   Gupta T;Gaitonde D M (Harish-Chandra Res Inst, , Allahabad-211 019) : Ultrasonic attenuation in cuprate superconductors. Pramana J Phys 2002, 58(5-6), 889-91.

Calculates the longitudinal ultrasonic attenuation rate (URA) in clean d-wave superconductors in the Meissner and the mixed phases. In the Meissner phase we calculate the contribution of previously ignored processes involving the excitation of a pair of quasi-holes or quasi-particles. There is a contribution α T in the regime K_B T <60><60> QUF <60><60> Δo and a contribution α 1/T in the regime QUF <60><60>K_BT <60><60> Δo. Finds that these contributions to the UAR are large and cannot be ignored. In the mixed phase, using a semi-classical description, calculated the electronic quasiparticle contribution to the UAR which at very low T, has a T independent term proportional to √H.

7 ref

017838   Gupta S V (National Physical Laboratory, , Dr. K. S. Krishanan Marg, New Delhi-110 012) : Hydrometers with variable mass and volume. MAPAN 2003, 18(2), 93-102.

The principle of method has been described to convert one single density hydrometer into hydrometers of higher denisity ranges. Errors at intermediate points have been calculated and the effect of errors in the inital hydrometers for other hydrometers has been given. Such a hydrometer is termed as variable mass and volume hydrometer. In a given range it works as a constant mass but variable volume hydrometer, while its mass is varied to change its range-the values of starting and final density.

2 illus, 5 tables, 3 ref

017837   Gupta A;Ganin A Y;Sharma P;Agnihotri V;Belova L M;Rao K V;Kozlov M E;Zakhidov A A;Baughman R H (Dep of Materials Sci, Royal Institute of Tech, Stockholm, Sweden) : Synthetic magnetic opals. Pramana J Phys 2002, 58(5-6), 1051-9.

Presents studies of novel nanocomposites of BiNi impregnated into the structure of opal as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. There exists no report in literature on any BiNi compound which is magnetic.

9 illus, 1 table, 5 ref

017836   Godwal B K;Modak P;Rao R S (High Pressure Physics Division Dep, Bhabha Atomic Research Centre, Mumbai-400 085) : On the electronic structure and equation of state in high pressure studies of solids. Bull Mater Sci 2003, 26(1), 175-81.

The high pressure behaviour of zinc as an interesting example of controversy, and of extensive interplay between theory and experiment have been discussed. Its room temperature electornic structure calculations have been presented is attributed to study the temperature effect on the occurrence of its controversial axial ratio (c/a) anolmaly under pressure, and the related electronic topological transition (ETT). A dense 63 x 63 x 29 k-point sampling of the Brillouin zone and it was found that the small (c/a) anomaly near 10 GPa pressure persisted at room temperature. A weak signature of the anomaly can be seen in the pressure-volume curve, which gets enhanced in the universal equation of state, along with taht of K-point ETTs. The change of slope in the universal equation of state near 10 GPa pressure, mainly to hybridization effects. The temperature effect in fact enhances the possibility of L-point ETT. That the L-point ETT was very sensitive to exchange correlation terms, and hence it is suggested that further refinements in the theorotical techniques are needed to resolve the controversies on the ETT in Zn.

6 illus, 48 ref

017835   Gangadhar Reddy G;ramakanth A;Ghatak S K (Dep of Physics, Kakatiya Univ, Warangal-506 009) : Magnetic-field-induced valuence transition in rare-earth systems. Pramana J Phys 2002, 58(5-6), 773-6.

The magnetic-field-induced valence transition in rare-earth systems has been investigated using the periodic Anderson model supplemented by the Falicov-Kimball term. This model has been solved by first decoupling the Falicov-Kimbal term as proposed by Khomskii and Koharjan and then taking the limit of infinite intra-site Coulomb repulsion. the valence transition both in the absence and in the presence of magnetic field as a function of temperature is studied. It has been fund that the system makes transition from non-magnetic to magnetic state when the magnetic field increases beyond a critical value Hc. The phase boundary defined in terms of reduced field Hc(T)/Hc(O) and reduced temperature T/T_v (T_v being the valence transitiion temperature in the absence of fields) is almost independent of the position of the localized level. The results are in qualitative agreement with experimental observations in Yb-and Eu-compounds.

1 illus, 10 ref

017834   Gaitonde D M;Modak P;Rao R S;Godwal B K (High Pressure Physics Division Dep, Bhabha Atomic Research Centre, Mumbai-400 085) : Electronic structure and superconductivity of MgB₂. Bull Mater Sci 2003, 26(1), 137-41.

Results of ab initio structure calculations on the compound, MgB₂, using the FPLAPW method employing GGA for the exchange-correlation energy are presented. Total energy minimization enables estimation of us to estimate the equilibrium volume, cla ratio and the bulk modulus, all of which are in excellent agreement with experiment. Mass enhancement parameter has been obtained by using D(E_F) and the experimental specific heat data. The T_c is found to be 37 K. A parameterized description of the calcualted band strucutre is issued to obtain the T=0K values of the London penetration depth and the superconducting coherence length. The calculated penetration depth by us is to small and the coherence length too large as comapred to the experimentally determined values of these quantities. This indicates the limitation of a the ory that relies only on electronic structure calculations in describing the superconducting state in this material and implies that impurity effects as well as mass renormalization effects need to be included.

1 illus, 25 ref

017833   Fuchs G etal (NO, , ) : Influence of disorder on superconductivity in non-magnetic rare-earth nickel borocarbides. Pramana J Phys 2002, 58(5-6), 791-7.

The effect of substitutional disorder on the superconducting properties of YNi₂B₂C was studied by partially replacing yttrium and nickel by Lu and Pt, respectively. for the two series of (Y, Lu)Ni₂B₂C and Y(Ni, Pt)₂B₂C compounds, the upper critical field Hc2(T) and the specific heat cp (T,H) in the superconducting mixed state have been investigated. Disorder is found to reduce several relevant quantities such as Tc, the upper critical field Hc2(O) at T = O and a characteristic positive curvature of Hc2(T) observed for these compounds near Tc. The Hc2(T) data point to the clean limit for (Y, Lu) substitutions and to a transition to the quasi-dirty limit for (Ni,Pt) substitutions. The electronic specific heat contribution γ(H) exhibits significant deviations from the usual linear γ(H) law. These deviations reduce with growing substitutional disorder but remain even in the quasidirty limit which is reached in the Y(ni_1-x, Pt_x)₂B₂C samples for x = 0.1.

5 illus, 16 ref

017832   Forgan E M;Charalambous D;Kealey P G (School of Phys and Astronomy, Univ of Birmingham, B 15 2 TT, UK) : The microscopic investigation of structures of moving flux lines by neutron and muon techniques. Pramana J Phys 2002, 58(5-6), 899-901.

Uses a variety of microscopic techniques to reveal the structure and motion of flux line arrangements, when the flux lines in low Tc type II superconductors are caused to move by a transport current. Using small-angle neutron scattering by the flux line lattice (FLL), one is able to domonstrate directly the alignment by motion of the nearest-neighbor FLL direction. This tends to be parallel to the direction of flux line motion, as had been suspected from two dimensional simulations. Also sees the destruction of the ordered FLL by plastic flow and the bending of flux lines. Another technique that collaboration has employed is the direct measurement of flux line motion, using the ultra-high-resolution spectroscopy of the neutron spin-echo technique to observe the energy change of neutrons diffracted by moving flux lines. The muon spin rotation (μSR) technique gives the distribution of values of magnetic field within the FLL. Succeeds in performing μSR measurements while the FLL is moving. Such measurements give complementary information about the local speed and orientation of the FLL motion. Concludes by discussing the possible application of this technique to thin film superconductors.

13 ref

017831   Eskildsen M R;Abrahamsen A B;Gammel P L; Bishop D J;Andersen N H;Mortensen K;Canfield P C (NO, , ) : Fluxline lattice symmetries in the borocarbide superconductor LuNi2B2C. Pramana J Phys 2002, 58(5-6), 903-05.

Compares the results of small angle neutron scattering on teh flux line lattice (FLL) obtained in the borocarbide superconductor LuNi₂B₂C with the applied field along the c- and a- axes. For H llc the temperature dependence of the FLL structureal phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field, H₂(T), rise sharply, bending away from H_c2(T) in contradiction to theoretical predictions of the two merging. For H llaa first order FLL reorientation transition is observed at H_tr = 3-3.5 kOe. Below H_tr the FLL nearest neighbor direction is parallel the b-axis, and above H_tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model.

2 illus 9 ref

017830   Esfarjani K;Chen Z;Kawazoe Y (NO, Sharif Institute of Technology, and Institute for Physics and Mathemat, Tehran, Iran) : Electronic properties of magnetically doped nanotubes. Bull Mater Sci 2003, 26(1), 105-7.

Effect of doping of carbon nanotubes by magnetic transition metal atoms has been considered. In the case of semiconducting tubes, it was found that the system has zero magnetization, whereas in metallic tubes the valence electrons of the tube screen the magnetization of the dopants: the coupling to the tube is usually antiferromagnetic.

2 illus, 1 tables, 8 ref

017829   Dutta Gupta N;Chaudhuri P (Energy Research Unit Dep, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700 032) : A structural analysis of the effect of Ar adn H₂ on microcrystalline growht in Si : H materials deposited in conventional PECVD chamber. Indian J Phys-Pt A 2003, 77(4), 319-25.

Evolution of hydrogen content and bonding have been studied in two sets of Si : H samples deposited near the amorphous (a-Si:H)-microcrystalline (μc-Si : H) boundary from hydrogen (H₂) and argon (Ar)-diluted silane (SiH₄) by varying the rf power in comventional (13.56 MHz) plasma enhanced chemical vapour deposition (PECVD). Microcrystallinity in the samples was verified by transmission electron microscopy (TEM). In H₂-diluted μc-Si : H smaples, the selective etching of SiH₂ by atomic hydrogen from the grain boundary has been observed. On the other hand in Ar-diluted samples, SiH₂ mode absorption increase of rf power. Appearance of the infrared absorption peak around 2030 cm^-1 in both H₂ and Ar-diluted samples, indicates that the platelet like configuration of Si-H bond may be associated with the growth of microsrystalline grains. Role of the metastable Ar in the growth of μC-Si : H has been discussed.

4 illus, 2 tables, 40 ref

017828   Dixit G P (National Physical Laboratory, , Dr. K. S. Krishnan Marg, New Delhi - 110 012) : Estimation of uncertainty in torque measurement - an application of universal approach. MAPAN 2003, 18(2), 83-92.

To harmonise the valutation and expression of uncertainty of measurement, describes the method of calculating the uncertainty in torque measurement for the calibration of various types of static torque measuring devices following the latest ISO/EAL guidelines of uncertainty evalutation, normally referred to as universal approach of uncertainty calculation. An elaborate case study for the calibration of a torque measuring device has also been presented.

5 tables, 7 ref

017827   Dhar S K;Chinchure A D;Alleno E;Godart C; Gupta L C;Nagarajan R (Tata Institute of Fundamental Research, Homi Bhabha Rd, Mumbai-400 005, ) : Possible coexistence of superconductivity and magnetic order in NdPt2B2C. Pramana J Phys 2002, 58(5-6), 885-8.

Coexistence of superconductivity and magnetic order been one of the exciting aspects of the quaternary borocarbide superconductors. So far RNi₂B₂C (R=Tm, Er, Ho and Dy) are the only known magnetic superconductors in this family. Presents resistivity, magnetization and heat capacity studies on NdPt₂B₂C (nominal composition, NdPt_1.5au_0.6B₂C and NdPt_2.1B_2.4C_1.2). Finds superconductivity in both samples with T_{c, onset} ~ 3 k. Bulk magnetic order is found to occur below 1.7 K. Suggests that NDPt₂B₂ is a possible magnetic superconductor.

2 illus, 6 ref

017826   Deepak;Balamurugan D;Nandi K (Materials and Metallurgical Engineering Dep, Indian Institute of Technology, Kanpur-208 016) : Variations in first principles calculated defect energies in GaAs and their effect on practical predictions. Bull Mater Sci 2003, 26(1), 169-73.

There is an abundant literature on calculations of formation and ionization energies of point defects in GaAs. Since most of these energies, especially the formation energies,a re difficult to measure, the calculations are primary means of obtaining their values. However, based on the assumptions of the calculations, the reported values differ greatly among the various calculations. The sources of errors and their impact on practical predictions valuable in GaAs device fabrication. In particular, a large set of computed energies and the most appropriate values have been selected. In the context of GaAs material quality, the impact of errors in calculation of formation energies on the preformance of the GaAs substrat for device fabrication was investigated. That in spite of the errors inherant in ab initio calculations, it is possible to correctly predict the behaviour of GaAs substrat.

4 illus, 1 tables, 12 ref

017825   Dash G N;Mishra J K;Mishra I P;Pattanaik S R (P G Physics Dep, Sambalpur University, Jyoti Vihar, Sambalpur-768 019, Orissa) : Optically controlled noise and small-signal behaviour of READ avalanche diode. Indian J Phys-Pt A 2003, 77(4), 387-91.

A new analytical model to study the effect of optical radiation on the noise behavior of a Read type IMPATT diode is presented. The application of this method to a Si-Read diode reveals some intersting features of reduction in the resonance like nouse peak due to optical injection.

4 illus, 1 tables, 13 ref

017824   Cui D F;Guo X X;Chen Z H;Zhou Y L;Yang G Z; Huang H Z;Zhang H X;Lui F Q;Ibrahim K;Qian H J (Laboratory of Optical Physics, Institute of Physics & Center for Condensed Matter Physics, Chinese Ac, Beijing-100 080, China) : Terminating atomic plane and growth mechanism study of perovskite oxide thin films by angle-resolved X-ray photoelectron spectroscopy. Asian J Spectrosc 2002, 6(1), 17-22.

A study terminating atomic plane and growth mechanism for the perovskite oxide thin films is reported. The ferroelectric BaTiO₃ (001) and the colossal magnetoresistance (CMR) La_0.9Sn_0.1MnO₃ thin films were grown epitaxially on SrTiO₃(001) substrate and LaAlO₃(001) substrate by pulsed laser deposition (PLD), respectively. The crystalline structure and the orientation of these oxide thin films were determined by X-ray diffraction. The topmost surface for the both of BiTiO₃ and La_0.9Sn_0.1MnO₃ thin films were analyzed by angle-resolved X-ray photoelectron spectroscopy (ARXPS), indicating that the BaTiO₃ film is predominantly terminated with TiO₂ atomic plane and the growth sequence of the atomic layers is TiO₂ (substrate) // BaO / TiO₂ / ..... / BaO / TiO₂; the La_0.9Sn_0.1MnO₃ film is predominatly terminated with MnO₂ atomic plane and the growth sequence of the layers is AlO₂ (sustrate) // La(Sn)O / MnO₂ / ...... / La(Sn)O / MnO₂. The evaluation for the LaNiO₃ thin film grown on the SrTiO₃ (001) substrate is also provided.

5 illus, 21 ref

017823   Cong B T;Huy P N A;Schelling P K;Halley J W (NO, Faculty of Physics, Hanoi University of Science, 334, Nguyen Trai Street, Hanoi, Vietnam) : Total energy calculation of perovskite, BaTiO₃, by self-consistent tight binding method. Bull Mater Sci 2003, 26(1), 155-8.

Results of numerical computation on some characteristics of BaTiO₃ such as total energy, lattice constant, density of states, band structure etc using self-consistent tight binding method have been presented. Besides storng Ti-O bond between 3d on titanium and 2p orbital on oxygen states, weak hybridization between the Ba 6s and O 2p states have been included. The results are compared with those of other more sophisticated methods.

6 illus, 2 tables, 14 ref

017822   Cong B T;Huy P N A;Long N H;Long D D (NO, Faculty of Physics, Hanoi University of Science, 334 Nguyenm Trai Street, Hanoi, Vietnam) : Simple explanation for the reentrant magnetic phase transition in Pr_0.5Sr_0.41Ca_0.09MnO₃ perovskite. Bull Mater Sci 2003, 26(1), 151-4.

The reentrant magnetic phase transition in Pr_0.5Sr_0.41Ca_0.09MnO₃ perovskite is explained using the Ising spin model on the square lattice with mixed ferromagnetic and antiferromagnetic exchange interactions. It is shown using numerical calculations that this effect is strongly by the external magnetic field and lattice disorder.

4 illus, 7 ref

017821   Chow R;Blindt R;Kamp A;Grocutt P;Chivers R (NO, Unilever Research & Development, Colworth House, Sharnbrook, Beds MK44 1LQ, United Kingdom) : Stimulation of ice crystallisation with ultrasonic cavitation microscopic studies. Indian J Phys-Pt A 2003, 77(4), 315-18.

While the capability of ultrasonic waves to stimulate crystallisation in various liquieds has been known for over 70 years, controlled experiments on the crystallisation of water are almost unknown, as are reports on the direct visulisation of the processes imvolved. The difficulty of setting up the experiments has been the major factor in the failure to date to identify the mechanism involved in the sonocrystallisation of water. Describes the first direct observations of the influence of ultrasonic cavitation on the production of secondary nuclei of ice from dendritic crystals. It has been achieved using a novel microscope measurement stage that not only permits controlled heating and cooling of the specimen, but also its simultaneous excitation with alternating pressures in the ultrasonic frequency range. Three distinct new phenomena have been observed to date. Firstly, there is a tendency for cavitation bubbles to form at the grain boundaries between the (hexagonal) crystals in the ice. Secondly, there is a process whereby the bubbles appear to eat their way into the ice, melting it as they progress; and thirdly, the dendritic structures are fragmented, thus multiplying the number of crystal nuclei in solution (Secondary crystallisation).

4 illus, 17 ref

017820   Chakraborti N;Prasad R (Physics Dep, Indian Institute of Technology, Kanpur-208 016) : Application of genetic algorithms to hydrogenated silicon clusters. Bull Mater Sci 2003, 26(1), 127-30.

Application of biologically inspired genetic algorithms has been discussed to determine the ground state structure of a number of Si-H clusters. The total energy of a given configuration of a cluster has been obtained by using a non-orthogonal tight-binding model and the energy minimization has been carried out by using genetic algorithms and their recent variant differential evolution. Results for ground state structures and cohesive energies for Si-H clusters are in good agreement with the earlier work conducted using the simulated annealing technique. The results obtained by genetic algorithms turn out to be comparable and often better than the results obtained by the simulated annealing technique.

1 illus, 17 ref

017819   Burghate D K;Deogaonkar V S;Sawarkar S B; Yawale S P;Pakade S V (Physics Dep, Polytechnic Badnera, Amravatti-444 701) : Thermally stimulated discharge current (TSDC) and dielectirc constant of semiconducting glasses. Bull Mater Sci 2003, 26(2), 267-71.

Results of thermally stimulated discharge current (TSDC) and dielectric constant for 40PbO-60Bi₂O₃ glass thermoelectrets are presented. Measurements of TSDC and dielectric constant, ε', have been carried out in the temperature range 30-300°C. The thermoelectrets were presented at different polarizing fields. The various observed peaks in the thermograms are discussed on the basis of space charge polarization. The trap energy is evaluated from the Garlick-Gibson plot of initial rise method. Similarly other parameters such as relaxation time, charge release etc are evaluated.

4 illus, 1 tables, 27 ref

017818   Briere T M;Sluiter M H F;Vijay Kumar;Kawazoe Y (NO, Institute for Materials Research, Tohoku University, Aoba-ku, Sendai-980 8577, Japan) : Structures of Mn clusters. Bull Mater Sci 2003, 26(1), 115-6.

The geometeries of several Mn clusters in the size range Mn₁₃-Mn₂₃ are studied via the generlized gradient approximation to density functional theory. For the 13- and 19-aton clusters, the icosahedral structures are found to be most stable, while for the 15-atom cluster, the bcc structure is more favoured. The clusters show ferrimagnetic spin configurations.

2 illus, 7 ref