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Polycrystalline Zn Zr substituted barium hexaferrite (BaFe12-xZnx/2Zrx/2O19 where x = 0.3, 0.5, 0.7 and 1.0) specimen have been synthesized by two different methods, namely conventional and microwave sintering. The latter has resulted in magnetoplumbite phase in 5 min at a lower temperature (1000 °C). The values of magnetic parameters of different samples are extracted from the corresponding M − H loops using law of approach to saturation magnetization. A high value of saturation magnetization (Ms = 76 emu/g) is obtained for a conventionally sintered sample. Still higher value of saturation magnetization (Ms = 104 emu/g) has been obtained for the microwave sintered cation substituted sample. The increase in the magnetization has been attributed to the magnetic reordering of iron cations in the non-magnetic Zn2+-Zr4+ substituted samples. The coercivity of the microwave processed substituted samples has been drastically reduced to 163 Oe (from 2961 Oe for conventionally sintered pristine sample). The observed decrement can be ascribed to the increase in particle size and reduction in magnetocrystalline anisotropy (2.58 × 106 erg/cc). Raman spectra of the substituted samples have shown a shift in the vibrational frequencies (characteristic of magnetoplumbite phase) with cation substitution. This suggests that the non-magnetic Zn Zr cations replace Fe3+ from certain interstitial sites (4f1, 4f2, 2b and 12k).

Nanocrystalline Ni1-xCoxFe2O4 (x = 0.0, 0.4, 0.5, 0.6, 1.0) samples were synthesized using sol-gel technique. X-ray diffraction (XRD) and vibrational spectroscopy techniques were employed to study the structure, cation distribution and ordering in the Co2+ substituted nickel ferrite (NCFO) samples. The XRD analysis of the specimen confirmed the formation of single cubic spinel phase. The substitution of Co2+ for Ni2+ cations resulted in the increase in lattice parameter. The distribution of cations in tetrahedral (A) and octahedral (B) sites in the unit cell was estimated using X-ray diffraction and Raman data. Infrared and Raman spectroscopies too confirmed the spinel phase formation in the samples. An observed systematic shift and asymmetric broadening in Raman spectra with a change in Co2+ concentration were correlated with different ligand parameters such as effective mass, bond length and force constant, etc. A Raman peak (A1g) was employed to estimate the Co2+/Ni2+ and Fe3+ distribution between the two interstitial sites. The estimation of cation distribution made by the two techniques (Rietveld refinement of X-ray diffraction data and Raman spectroscopy) is in very good agreement. It is revealed that nickel ferrite (NFO) is nearly inverse (96% Ni2+ on B-sites). The substitution of Co2+ in NFO results into a partially inverse mixed ferrite phase with Co occupying nearly 18% A-sites in Ni0.5Co0.5Fe2O4 and 25% in CoFe2O4.

Tin oxide films with thicknesses in the range from 5 to 110 nm have been deposited by reactive dc magnetron sputtering of Sn in Ar + O plasma at a low working pressure of 1.0× 10 −3 Torr on glass substrates at different temperatures (150–400 °C). The effect of deposition time, substrate temperature, and oxygen partial pressure on surface morphology , crystallographic structure, optical properties, and photoluminescence characteristics of SnO 2 films has been studied and correlated with their defect structure . The structural transformation from nanocrystalline to polycrystalline of thicker films >40 nm and films were grown at higher temperature is explained based on adatom mobility and uniform substrate coverage. Based on photoluminescence characteristics and transmittance spectra, the 20 nm thick film exhibits the least defect structure and best electronic and optical behaviors.

In this paper we report the structural, vibration, and electronic-structure parameters (bonding and valence of cations) of single phase cubic mixed spinel nanoparticles of (ZnδMnγFe1−(γ+δ))[NixZn0.5−δMn0.5−γ−xFe1+(γ+δ)]O4 where x = 0.05–0.45 with an aim to determine cation-distribution i.e. δ and γ in these samples. The Raman spectroscopy has established that only Fe and Zn cations occupy tetrahedral interstitial sites in a FCC anion lattice in nearly equal fraction, and Mossbauer spectra have shown that Fe3+ cations are present at both, tetrahedral and octahedral interstitial sites and Ni2+ cations are situated at the octahedral sites in all the substituted samples. The photoelectron spectra also revealed the presence of Fe3+ cations at both the interstitial sites. The best possible cationic distribution in Ni substituted Mn–Zn ferrites has been estimated by reiteratively calculating the intensity ratios of various pairs of X-ray diffraction peaks and matching with the observed intensity ratios.

A study of electron- and magneto-transport behavior of ultrathin SnO 2 films of thickness ≤40 nm with high conductivity of 537 Ω −1 cm −1 deposited on glass substrate by using DC reactive sputtering has been carried out at low temperature. Hall effect measurements revealed these SnO 2 films to be degenerate down to 40 K. The films with thickness >5 nm are found to undergo a metal-semiconductor transition below 140 K, and show a negative MR of ∼1.5% at a magnetic field of 0.9 T below 40 K. Both these phenomena have been ascribed to the presence of weak localization of electrons at low temperature. Electron transport behavior has been explained using quantum correction to conductivity. Estimated inelastic scattering lengths were found to be longer than the film thickness which supports two-dimensional nature of electron- and magneto-transport in these ultrathin films.

In the present paper an attempt has been made to understand the growth mechanism of SiGe alloy nanowires synthesized in H-mode cylindrical microwave cavity resonator at 900 °C in a short time of nearly 5 min. The role of ambience, microwave H-field, duration of interaction with microwaves and germanium concentration in the starting precursor have been investigated. It is believed that H-field of microwaves efficiently interacts with the starting precursor powder in air ambience and results in superheating/supersaturation, which gives rise to the formation of innumerable critical sized nuclei via heterogeneous nucleation, leading to one dimensional growth of cylindrical nanowires.

The effect of substitution of Mg–Zr for Fe in M-type barium hexaferrite (BHF) and of processing technique on the magnetic properties and microstructure has been reported in the present paper. Significant changes in magnetic properties have been observed on substituting Fe ions by Mg and Zr ions in M-type barium hexaferrite, i.e. BaFe 12 O 19 as well as by single mode microwave processing. The single mode microwave processing of the undoped sample reduced the coercivity to nearly 25% of the value for the sintered sample along with the enhancement in magnetization, thereby making it suitable for memory devices. The improvement in magnetic properties is explained on the basis of microstructure. The addition of substituents, though assisted in the formation of single phase, it, however, degraded the magnetization besides decreasing the coercivity, possibly due to substitution at the octahedral sites.

The present paper deals with the study of photoluminescence (PL) and the other physical properties (structural, electrical and optical) of SnO2 thin films with controlled disorder and intrinsic defects induced during the reactive magnetron sputtering by changing oxygen flow rate from 12 to 16 sccm. The changes in unit cell volume, near band-edge optical transparency and width of Urbach tail in the films are correlated with the structural disorder and presence of intrinsic defects induced by growth under different oxygen partial pressures. The increased intensity of the PL near UV emission and decrease in the intensity of visible emission peaks with increase in oxygen flow rate is linked with the decrease in oxygen vacancies and tin interstitials in the films. With increasing oxygen content, whereas the electrical resistivity of the films minimizes to a value of 4.3 × 10−2 ohm cm at 14 sccm, the mobility of the films increases to a saturation value 15 cm2 V−1 s−1. The donor-defect concentration linked carrier density is observed to decrease monotonically from 2 × 1019 to 0.6 × 1019 cm−3.

Silicon germanium alloy has successfully been synthesized in a 2.45 GHz, single mode microwave H field at 900 °C in 5 min in the Microwave Laboratory. The phase formation occurs at a temperature which is lower by 400 °C than its equilibrium temperature. In the present paper an attempt has been made to understand the mechanism of rapid alloying of Si and Ge at a much lower temperature in microwave H field. The shape and size of starting particles play a significant role in microwave absorption. It is proposed that the interaction of H field at 2.45 GHz first induces B-field in the irregular shaped precursor powder particles of different sizes; the gradient in induced magnetic flux generates circulating electric field. Consequently, dipolar losses are induced by local electric field in the pellet, which generate heat and culminate into rapid alloying of Si and Ge (nonferric diamagnetic elements). Furthermore, magnetic reorientation of diamagnetic fine particles by H-field at 2.45 GHz assists in an efficient heating of the Si and Ge powders and results in alloy formation at a much lower temperature.

This paper reports the charge transport mechanism at low temperatures in (110) oriented polycrystalline tin oxide (SnO 2 ) films of less than 100 nm thickness prepared by reactive sputtering in the substrate temperature (T S ) range of 350–450 °C. Undoped tin oxide films with high electrical conductivity of 11 Ω –1 cm –1 have been achieved at 350 °C. The Hall mobility increases from 6.7 to 13.9 cm 2 /V·s and carrier concentration decreases from 11 × 10 18 to 0.9 × 10 18 cm –3 as T S is increased. In the 300–100 K temperature range we found two types of conduction mechanisms: thermally activated conduction till 160 K and nearest-neighbour-hopping conduction below 160 K. At temperatures below 90 K, the Mott variable-range-hopping (VRH) conduction governs the charge transport. In all the three regimes the activation energies of conduction increase with an increase in T S , being 15–50, 0.2–9, and 2–6 meV respectively, consistent with a decrease in oxygen vacancies at higher T S . The analysis of the data in Mott VRH conduction regime suggests a systematic localization of the oxygen vacancy states with an increase in growth temperature. Even at 70 nm thickness the films behave as three dimensional with regard to the Mott VRH conduction process.

This paper presents our results on the significant effect of application of electric field during deposition on various properties of thin SnO2 films, especially in the ultrathin regime. SnO2 films of 25-75 nm deposited on glass substrates without and with the presence of electric field (32 V/cm) during deposition were compared. It is found that the presence of field has improved the crystallinity and stoichiometry of the film along with its transmittance. Significantly high mobility of 43 cm2/V.s at low thickness of 25 nm resulted in a reasonably low resistivity of 1.5 ohm-cm as a consequence of the field assisted growth.

In the present paper, DC magnetization investigation on the insulating nanocrystalline powder samples of Ti 1− x Mn x O 2 ( x = 0, 0.05, 0.10, and 0.15) prepared by simple chemical route is reported. Structural measurements revealed phase pure anatase structure of TiO 2 when x ≤ 0.05 and a mixture of anatase and rutile TiO 2 along with the signature of Mn 3 O 4 phase for x > 0.05. Magnetic measurements exhibited the presence of ferromagnetic ordering at room temperature in samples having either small fraction of Mn or no Mn at all. This ferromagnetic signature is accompanied with paramagnetic contribution which is found to dominate with increase in Mn concentration. The Ti 1− x Mn x O 2 sample having highest Mn concentration of x = 0.15 showed nearly paramagnetic behavior. However, at low temperatures, additional ferrimagnetic ordering arising due to Mn 3 O 4 ( T C = 42 K) is evidenced in the doped samples. Consistent with the XRD investigations, the isofield DC-magnetization measurements under field cooled and zero field cooled (FC–ZFC) histories corroborated the presence of Mn 3 O 4 phase. Also, distinct thermomagnetic irreversibility has been observed above 42 K. These results are suggestive of presence of weak ferromagnetic ordering possibly due to defects related with oxygen vacancies.

Room-temperature ferromagnetism has been observed in Co- or Mn-doped SnO 2 and Co- and F-co-doped SnO 2 thin films. A maximum magnetic moment of 0.80 μ B /Co ion has been observed for Sn 0.90 Co 0.10 O 1.925− δ F 0.075 thin films, whereas in the case of Sn 1− x Mn x O 2− δ it was 0.18 μ B /Mn ion for x =0.10. The magnetization of both Sn 1− x Co x O 2− δ and Sn 1− x Co x O 2− y − δ F y thin films depends on the free carrier concentration. An anomalous Hall effect has been observed in the case of Co-doped SnO 2 films. However, the same was not observed in the case of Mn-doped SnO 2 thin films. Carrier-mediated interaction is convincingly proved to be the cause of ferromagnetism in the case of Co:SnO 2 . It is, however, proposed that no carrier-mediated interaction exists in the case of Mn:SnO 2 . Present studies indicate that dopants and hence electronic cloud–lattice interaction plays an important role in inducing ferromagnetism.

In the present paper, the preliminary investigations of a series of ZnO thin films co-doped with indium and cobalt with an objective to elucidate the correlation, if any, between the carrier concentration and the induced room temperature ferromagnetism (RTFM), are presented. The single-phasic (Zn 99.5 In 0.5 ) 1− x Co x O thin films are deposited by spray pyrolysis. The substitution of Zn 2+ by Co 2+ has been established by optical transmission analysis of these films. The films are ferromagnetic at room temperature; and the magnetization has higher value for indium and cobalt co-doped thin film as compared with Zn0 90 Co 0.1 O thin film (having no indium).

The present work discusses the successful electrodeposition of Cu/Co multilayers, exhibiting appreciable GMR of 12–14% at room temperature. The effect of individual Cu and Co layers on the magnitude and behavior of GMR has been studied. By varying the thickness of individual layers the field at which saturation in GMR is observed can be controlled. It was observed that for lower thicknesses of Co layer, the saturation fields are reduced below 1 kOe. The Cu layer thickness seems to control the nature of magnetic coupling and the saturation field, with the two showing a correlation.

Nanostructured Nickel–Zinc ferrite of composition Ni0.65Zn0.35Fe2O4 was prepared by sol–gel, co-precipitation, citrate-gel and oxalate precursor methods. X-ray diffraction (XRD) patterns of all the samples showed the spinel structure. A comparison of average crystallite size clearly indicated that the sol–gel method was the effective one in producing small crystallite sized samples having insignificant variation with annealing or sintering temperatures. Also, sol–gel method was observed to provide high saturation magnetization values in samples sintered even at lower temperatures. The high magnetization values are, in general, reported in bulk samples prepared at higher sintering temperatures by conventional ceramic method. Direct-current (DC) resistivity of these samples was also considerably improved as compared to that of the bulk materials. Discussion has been made on the basis of observed higher values of saturation magnetization and dc resistivity towards the development of a high-quality core material useful for high-frequency applications.

Thin films of lithium ferrite (with general composition Li0.5Fe2.5O4) were fabricated at low temperatures (up to 650 °C) by citrate-route using spin-deposition technique. Deposited films consisted of nanometer-sized grains as evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. XRD patterns for annealed films showed broad peaks exhibiting a spinel phase. Size of nanocrystallites is estimated to be 3–7 nm using Scherrer's equation. Average grain size ∼8.5 nm is observed from TEM images of films annealed at 650 °C. Scanning electron micrographs show the formation of spherical aggregates of around 130 nm in diameter. The AFM analysis clearly evidenced the development of nanograins even at low (∼500 °C) annealing temperatures. Significant decrease in complex dielectric permittivity (∈′ − j∈″) with frequency is observed in the low frequency (100 Hz–1 MHz) as well as in X-band microwave frequency (8–12 GHz) region. ∈′ is found to be in the range of 15.7–33.9 in low frequency region, whereas in X-band microwave frequency region, it is found to lie between 3.9 and 4.9. Similarly, ∈″ is found to be 0.16–5.9 in the low frequency region, and 0.002–0.024 in the X-band microwave frequency region. Room temperature dc resistivity of these films is estimated to lie in the range of 106–108 Ω cm. These results strongly suggest that citrate-route processed nanocrystalline lithium ferrite thin films are promising candidates for monolithic microwave integrated circuits (MMICs).

Nanocrystalline nickel ferrite and zinc doped nickel ferrite thin films with general composition Ni 1− x Zn x Fe 2 O 4 ; x =0.0, 0.2 and 0.5 were fabricated by the spin-deposition technique. Citrate precursor method was adopted to prepare coating solution used for film deposition. This method resulted in single phase, transparent, homogeneous and crack-free nanocrystalline ferrite thin films at annealing temperature as low as 400 °C. The substrates used for film deposition were ITO-coated 7059 glass, fused quartz and Si (1 0 0). The thickness of films was found to be in the range ∼1000–5500 A. The surface microstructure and morphology investigated by atomic force microscopy (AFM) confirmed the grain size of nickel–zinc ferrite films to be in nanometer range indicating nanocrystalline nature of the films. Dielectric properties such as the real (∈′) and imaginary parts (∈″) of complex permittivity were measured in the X-band microwave frequency region (8–12 GHz) by employing extended cavity perturbation technique. The M – H hysteresis measurements on the films annealed at 650 °C revealed narrow hysteresis curves with H c and M s varying for different compositions.

Room temperature ferromagnetism (RTFM) has been thoroughly examined in a series of polycrystalline (ZnO)1−x(MnO2)x samples prepared by solid-state reaction method. All these samples, covering a wide range of MnO2 concentration, viz., 0.01 ≤ x ≤ 0.97 , calcined at 400 ∘C are found to possess some ferromagnetic contribution in their M – H behaviour. A typical ferromagnetic behaviour in the isothermal measurements of magnetization performed on a few samples at temperature as high as 200 ∘C, not reported hitherto, indisputably corroborates that the Curie temperature T C is greater than 200 ∘C. The saturation magnetization of the FM contribution in these samples appears to be governed by the initial amount of MnO2 (and not of ZnO) employed for their synthesis. With sintering at higher temperature, the FM fraction disappears in all these samples — a fact, which is indicative of the metastable or inhomogeneous nature of the observed RTFM. These detailed investigations substantiate the emerging consensus that the origin of ferromagnetic ordering in ZnO:Mn system is extrinsic in nature.

Fine powders of Ni0.6 − xCuxZn0.4Fe2O4, where 0 ≤ x ≤ 0.4 was prepared by the citrate precursor method. The powders were calcined at 600 °C for a duration of 1 h and sintered at 900 °C for 3 h. The effect of compositional variation on structural, dielectric and magnetic properties of the Cu substituted NiZn ferrite was investigated. X-ray diffraction measurements confirmed the formation of single-phase cubic spinel structure at such low temperature of calcinations and sintering. A maximum density of 4.7 g/cm3 was obtained for the Cu substituted ferrite. The grain sizes were estimated from the SEM micrographs. The addition of copper promoted grain growth, resulting in increase in grain size. Curie temperature, however, was understandably lowered with the increase in Cu content. A saturation magnetization value of 92 emu/g was obtained for the composition x = 0.2. This value is higher than that reported for ferrites prepared by the conventional ceramic method. Ferrite with Cu concentration of x = 0.4, showed the highest value of initial permeability.

Room-temperature ferromagnetism (RTFM) is investigated in the polycrystalline bulk (ZnO) 0.98 (MnO 2 ) 0.02 samples prepared by a modified solid-state sintering route. Successive sintering of a sample was carried out in air at different temperatures in the range of 400–1000 °C. The study of magnetization and phase-investigation in the sample was carried out after each sintering step. The progressive suppression of impurities and the consequent reduction in RTFM is clearly observed in the samples with increase in the sintering temperature up to 800 °C. The subsequent successive sintering of the (ZnO) 0.98 (MnO 2 ) 0.02 sample up to 1000 °C yields fully paramagnetic sample exhibiting wurtzite structure. The studies support the conjecture (Kundaliya et al., Nat. Mater. 3 (2004) 709 [18] ) that RTFM in this system has an origin related to a randomly distributed impurity phase produced by local dissolution of ZnO and MnO 2 .

Nanocrystalline nickel–zinc ferrite thin films with the general formula Ni 1− x Zn x Fe 2 O 4 , where x =0.0, 0.2, 0.4 and 0.6 were fabricated via a chemical route known as the citrate precursor route. These films were spin-deposited on indium–tin oxide coated glass, fused quartz and amorphous Si-wafer substrates, and annealed at various temperatures up to 650 °C. The films annealed below 400 °C were found to be X-ray amorphous, while the films annealed at and above 400 °C were polycrystalline exhibiting a single-phase spinel structure. The average grain size of the films evaluated by transmission electron microscopy, is found to be in the range 4–8.5 nm. The room temperature DC resistivity of the films is in the range 10 3 –10 7 Ω m. Dielectric constant and dielectric loss were measured in the frequency range 100 Hz–1 MHz. Dielectric constant of the films is found to lie between 25 and 44, while the loss factor is if the order of 10 −2 . The higher values of the dielectric constant for films having higher zinc concentration are attributable to the enhanced hopping between Fe 2+ and Fe 3+ ions in these samples. The M–H hysteresis measurement of the nickel ferrite thin films annealed at 650 °C showed narrow hysteresis loop—a characteristic of soft ferromagnetic material.

Dense and crack-free substituted lithium ferrite–polymer composite films of thickness ∼80 μm were fabricated. The substituted lithium ferrite powders with general composition Li 0.5− x /2 Co x Mn 0.1 Fe 2.4− x /2 O 4 , where x = 0.0 , 0.2, 0.4 and 0.6, were prepared by citrate-route. Epoxy resin EPG-280 was used as a polymer. The composite films required lower processing temperature ∼100 °C. Cavity-perturbation technique was employed to measure the complex permittivity ( ∈ ′ – j ∈ ″ ), and the complex permeability ( μ ′−j μ ″), of the composite films at X-band microwave frequencies (8–12 GHz). The dispersion in the complex permittivity of ferrite composite films was found to be significant. The maximum value of ∈ ″ was observed for the film with x = 0.6 and 75% volume loading of ferrite component. The permeability μ ′ of films was found to decrease with an increase in frequency as well as with the volume loading of ferrite component in composite films. The single-phase spinel structure of the substituted lithium ferrite powders for compositions x = 0.0 , 0.2, 0.4 and 0.6 was confirmed by X-ray diffraction pattern. The microstructure of composite films was observed by scanning electron microscopy.

Polycrystalline cobalt-substituted lithium ferrites with general formula Li0.5−x/2CoxFe2.5−x/2O4 (x = 0.0, 0.2, 0.4 and 0.5) were prepared by a non-conventional citrate precursor method, which is advantageous over conventional (solid state sintering) method because of low temperature (600 ° C) processing. Small amounts of Bi2O3 (0.5 wt.%) were added to reduce the porosity and dielectric loss tangent at sintering temperatures (1000–1200 °C). The complex magnetic permeability (μ′ − jμ″) and complex dielectric permittivity (ϵ′ − jϵ″) of cobalt-substituted lithium ferrites were measured in the 8–13 GHz microwave frequency range. The systematic variations of the real and imaginary parts of both permeability and permittivity with frequency and composition have been analyzed. The minimum value of ϵ′ ∼ 11.3 measured for x = 0.4 substituted lithium ferrite is observed for a sample sintered at 1000 °C. The highest values of ϵ′ and ϵ″ were observed for samples sintered at 1200 °C. μ′ varies between 1.84 and 3.90 for pure and cobalt-substituted lithium ferrite bulk ceramics. The spinel structure of the samples was confirmed by X-ray diffraction (XRD).

Ferromagnetic nanomaterials are of particular interest, because at nanoscale a crystallite can exhibit a single magnetic domain. These nanomaterials therefore exhibit different magnetic properties as compared to bulk. Recently, barium ferrite has gained importance due to its potential use in magnetic recording and in microwave devices. Barium ferrite nanoparticles are prepared by the citrate precursor method by varying the pH of the solution and calcination temperature. The effect of particle size and capping reagent on the structural, dielectric and magnetic properties of the resulting barium hexaferrite particles has been studied, and reported in the present paper.

Thin films of Cu–Co have been electrochemically deposited onto Cu-coated alumina substrates in a single sulfate bath. Electrochemical process parameters are expected to influence the chemical composition and microstructure and hence, physical properties of the films. We have attempted to study and understand the effect of various electrochemical process parameters like bath composition, bath temperature, deposition current density and pH of the electrolyte, along with annealing temperature and time on the magnitude of GMR in Cu–Co films. The maximization of GMR is understood in terms of an optimum distribution of the size and the separation of the magnetic particles via the thermally-induced phase segregation.

Epitaxial thin films of YBa 2 Cu 3 O 7– δ (YBCO) have successfully been grown by reactive RF-magnetron sputtering technique at a low pressure (0.95 mTorr) with T C ( R =0)=85.3 K and J C mag (4.2 K)≈2×10 7 A/cm 2 . The incorporation of oxygen in the as-grown films has been controlled by using different ambient—oxygen, air and argon—during in situ cooling. The superconducting behavior of the resulting films was studied using resistance–temperature and low field a.c.-susceptibility measurements and correlated with their structure. All the films exhibited metallic conduction in the normal state. The oxygen- and air-cooled films were superconducting, and exhibited usual orthorhombic structure, but the argon-cooled films were non-superconducting and possessed tetragonal structure. This implied that the structure of the film during deposition is tetragonal, and transforms to either of the oxygen rich orthorhombic-I or -II phases depending upon the oxygen/air ambient. The ‘ δ ’ values of 0.14, 0.32 and 0.70 and higher ‘ c ’-parameters of 1.1785, 1.180 and 1.183 nm have been obtained for oxygen-, air- and argon-cooled films, respectively.

High quality Cu–Co alloy films with excellent metallic luster have been electrolytically deposited directly onto n-Si (1 0 0) substrate, thereby eliminating the need of a conducting seed layer, which is otherwise required when the films were grown on insulating substrates (Al 2 O 3 ). The as-deposited Cu–Co films exhibit relatively higher magnetoresistance (MR) in comparison with the as-deposited films on Al 2 O 3 under identical conditions. The observed increase in MR could be attributed to the reduced substrate current shunting. The MR further improves to 2.67% (at H =10 kOe) with vacuum annealing (at 425°C for 30 min) of the films on Si. This has been ascribed to the separation of Cu and Co phases resulting in a magnetic granular nanostructure. This value of MR of annealed films on Si is, however, lower in comparison with the value obtained for annealed films deposited on Al 2 O 3 . Glancing angle X-ray diffraction (GAXRD) has revealed the formation of copper silicide in these samples, which is responsible for the lower value of MR. Thus we have observed good MR with a copper silicide host matrix.

Cu–Co granular films have been prepared by galvanostatic dc electrodeposition in a single sulphate bath. The magnetoresistance ratio (MR={( R H − R 0 )/ R 0 }×100) increased with increase in annealing temperature until 450°C, beyond which MR starts decreasing. Lower coercivity values along with non-saturating behaviour of the room temperature magnetization curves indicated the presence of an appreciable amount of superparamagnetic clusters. The average cluster size was calculated by fitting the superparamagnetic component of magnetization to Langevin equation. The average radius of the Co clusters (assuming spherical shape) was calculated to be 1.87 nm for an as-deposited film and 1.57 nm for a film annealed at 400°C for 1 h. The lowering of average cluster size with increase in annealing temperature in the metastable films is attributed to the segregation of many new (smaller) Co clusters.

We have been able to prepare ultrafine powders of pure and doped La 0.67 Ca 0.33 MnO 3 (LCMO) at a relatively lower temperature of 550°C using a simple, cost effective and versatile PVA-based chemical route. A maximum magnetoresistance (MR) ratio of −25% is obtained at 20 K in a magnetic field of 3 kOe. Magnetoresistive behaviour being retained in the nanopowders may have implications for enhancing data storage capacity. The semicondutor-to-metal transition temperature, T p , however, shifts towards the lower temperature as the particle size is reduced. To improve T p and near-room-temperature MR additives like NH 4 NO 3 and citric acid have been used. In addition, Pb is substituted for Ca.

Cu–Co alloy films have been electrodeposited galvanostatically from a single sulphate bath. XRD reveals the as-deposited films to be single phasic metastable FCC alloy of Cu and Co with a grain size of 5–20 nm. Phase separation on annealing forms fine Co granules at the core of Co-rich shells. The grain size grows to 40–60 nm after annealing at 400°C for 1 h. A total phase separation into Cu (FCC) and Co (FCC) is observed after annealing at 700°C. Maximum room-temperature magnetoresistance (MR) of 4% at a magnetic field of 10 kOe was observed for film annealed at 450°C for 1 h. A MR ratio of 7.8% was observed at 20 K in a magnetic field of 3 kOe. The MR was observed to increase with film thickness. Coexistence of typical superparamagnetic and ferromagnetic features is observed in the room-temperature magnetization curves of as-deposited and 400°C annealed films.

In the present work, Si0.95Ge0.05 alloy nanowires were synthesised in a single-mode resonant cavity operated in H 011 mode in ambient at 2.45 GHz in a short duration (5 min) and at a temperature (900 ◦ C) lower than the equilibrium alloy-phase formation temperature. The photoluminescence (PL) studies were carried out at room temperature. The intense PL peaks, in the energy range of 2.9–3.6 eV, can be ascribed to radiative recombination of the generated carriers. The low temperature (100–250 K) dc electrical-transport is investigated; and the activation energy is estimated to be lower by an order than that of polycrystalline samples. The lower activation energy is possibly due to electronic/structural defects introduced by the non-equilibrium growth process and high aspect ratio of the grown nanostructure. With these improved characteristics, the alloy nanowires can be exploited for device fabrication.

This paper describes the performance of an alternative capacitive pressure gauge using lead iron tungstate as a capacitive element over a pressure range of 418 MPa. A commercial strain gauge pressure transducer is used to get the consistency in the calibration equation of the pressure transducer using the piston gauge pressure standard when compared with the calibration equation of the pressure transducer obtained using the capacitive pressure gauge. A close agreement better than 1×10 −3 (over all accuracy of the pressure transducer is ±5×10 −3 ) demonstrate for the first time the use of the capacitive pressure gauge as a reliable pressure standard where the required accuracy in the pressure measured is below 1×10 −3 .

In-situ superconducting c-axis oriented YBa2Cu307_s (YBCO) thin films have been grown at T sub = 775 °C on SrTiO3(100) and MgO(lOO) by r.f.-magnetro n sputtering at an oxygen partial pressure, which not only lies below the stability line but is more than an order of magnitude lower than its empirically suggested limit. The effect of variation in partial pressure of oxygen (POl) on the film characteristics is analyzed by employing a.c.-magnetic susceptibility, resistance-temperature variation, Rutherford backscattering, atomic force microscopy (AFM), scanning electron microscopy and X-ray diffraction techniques. The oxygen deficiency, 5, is calculated employing a number of techniques. The higher c-axis lattice parameters of the films are supportive of antisite disorder in the cations. The AFM investigations have established that Stranski-Krastanov-type growth mechanism is operative in the present case. The variation in critical current density (J™g(T)) with temperature is reported for the first time in the low pressure sputtered films exhibiting a J craas(43 K) of «4.6X 106 A cm" 2.

The epitaxial films of YBCO grown by low pressure (∼ 10 −3 Torr) rf-magnetron sputtering, exhibiting ‘c’- axis lattice parameter 11.753 A and 11.718 A on MgO(100) and SrTiO 3 (100), respectively, were subjected to the Rutherford backscattering technique (RBS) for their compositional analysis. The backscattering-simulations performed on these films have revealed a gradient in the concentration of both Ba and Cu cations across the thickness of the film. The cation ratios (Ba:Y and Cu:Y) in the films grown on different substrates are found to be substrate dependent. In this paper, an attempt has been made to correlate the observed cation deficiencies with the employed experimental conditions. It is conjectured that the observed cation deficiency is expected to give rise to ‘Y-for-Ba’ replacement, thereby resulting in the extension of the c -axis parameter. This atomic disorder (replacement) also explains the observed lower values of T c .

Large (8×1.5×1.5 mm 3 ) single crystals and platelets (3×3×0.1 mm 3 ) of YBa 2 Cu 3 O 7- x were grown from a suitable flux composition and appropriate thermal cycle in an alumina crucible. The crystals were investigated for their micro- and nano-structures by employing scanning electron microscopy (SEM) and scanning tunneling microscopy (STM), respectively. The topographic investigations revealed that a layer-by-layer growth mechanism is operative for the growth of these single crystals.

Thin films of amorphous (a-) Ge20Se80 − xBix (x = 4,10) and a-As2Se3 − xBix (x = 0.2, 0.5) have been prepared by thermal evaporation and characterized for their electrical and optical properties. The addition of bismuth, in excess of 4 at.%, to p-type a-Ge20Se80 and a-As2Se3 films results in large (several orders of magnitude) changes in the electrical conductivity and conversion of the conductivity from p to n type. A correlation of the electrical and optical data of the modified films suggests that the addition of bismuth causes a Fermi level shift and the electrical transport is predominantly due to hopping of electrons after being excited into localized states the conduction band edge.

Amorphous silicon-germanium (a-Si 1− x Ge x ) thin films have been prepared co-sputtering a composite target of high purity crystalline silicon (c-Si) and c-Ge using ion beam sputtering technique. The desired composition has been obtained by suitably adjusting the exposed areas of c-Si and c-Ge. The electrical, optical and structural properties of these films have been investigated as functions of composition (for a-Si 1- x Ge x ) and ion beam energy-voltage and substrate temperature (for a-Si 50 Ge 50 ). The amorphous silicon-germanium films deposited with increased x or decreased beam voltage and/or substrate temperature, in general, exhibit an increase in their electrical conductivity. The conduction mechanism associated with these films is dominated by hopping between the localized states. The a-Si 50 Ge 50 films deposited at a beam energy of 1000 V and substrate temperature of 300°C have a band gap and an electrical conductivity of 1.1 eV and 3 × 10 −5 (Ωcm) -1 respectively.

Infrared and spectroscopic ellipsometric studies have been done on thin films of hydrogenated amorphous silicon (a-Si:H), germanium (a-Ge:H) and silicongermanium alloy of a typical composition (a-Si28Ge72:H) prepared by reactive ion beam sputtering (RIBS). Films deposited at increasing H2:Ar flow ratio generally show enhanced dihydride and polyhydride bonding and a decreased value of e2max. A correlation of the two results reveals that the increase in hydrogen content affects the growth process considerably and makes the films density deficient and inhomogeneous by increasing the volume fraction of voids, network strains and vacancies. The a-Si28Ge72:H films deposited at increasing H2:Ar flow ratio show a preferential attachment of hydrogen to silicon rather than to germanium. It has been found that RIBS-prepared films are more density deficient as compared to films deposited by glow discharge, owing mainly to the presence of dihydride species.

The effect of addition of Pb on zero resistance temperature, Tc (R=0), lattice parameters and stability of Bi2PbxSr2Ca2Cu3.1Oy superconductors is studied for x varying from 0.0 to 0.8 in the starting composition. The addition of Pb enhances the high Tc phase and a maximum Tc (R=0) of 105K is observed for the sample prepared with x=0.6. The lattice parameters of low and high Tc phases are aL = 5.40A°, bL = 5.42A°, cL = 30.70 A° and aH = 5.40 A°, bH = 5.42 A°, cH = 37.36 A°, respectively. A systematic variation in lattice parameters with addition of Pb has been observed. Lead containing samples exhibit a higher value of critical current (Ic) as well. On the basis of fractional changes in Ic and Tc (R=0) with exposure of superconducting sample to ambient conditions of atmosphere upto 50 days, it has been inferred that high Tc phase is most stable in the sample corresponding to 0.6Pb.

Fluctuation effects and temperature dependance of IV characteristics of c-axis oriented YBCO thin films on STO(100) have been investigated within the context of unbinding of vortex-antivortex pairs in the Kosterlitz-Thouless transition (KT) and Aslamazov-Larkin (AL) model. A critical jump in the nonlinearity parameter, α (V=Iα), is found at the universal value of α = 3. The broadening of the jump in the temperature dependance of α and associated exponential inverse square root temperature dependance of resistivity above Tc indicate quasi bi-dimensional behavior in the YBCO system. The correlation between AL fluctuations and phase fluctuations (KT model) has also been studied.

A systematic study of the effect of humid atmosphere on the stability of various phases of BSCCO system is reported. Samples exhibiting single 2223 phase were found to be insensitive to humid atmosphere, whereas multiphasic samples as well as samples having only 2212 phase showed the presence of Bi 2 CuO 4 , SrCO 3 , CaCO 3 and CuO and lowering of Tc. The formation of impurity phases in the degraded multiphasic samples is ascribed to the decomposition of 2212 phase.

Physical properties of hydrogenated amorphous silicon (a-Si:H) films prepared ion beam sputtering under varying H 2 :Ar flow ratios and various substrate temperatures are reported. Ellipsometric studies reveal that both the increase in H 2 :Ar flow ratio and decrease in substrate temperature lead to density-deficit films. The films are poorly photoconducting due to the presence of defect centres created possibly by SiH 2 , (SiH) 2 n and SiO species in the midgap.

Electrical and infrared (IR) properties of hydrogenated amorphous germanium (a-Ge:H) films prepared by reactive ion beam sputtering of a high-purity crystalline germanium target under varying deposition conditions have been studied. Minimum conductivity (10-4ω-1cm-1) a-Ge:H films have been obtained for H2:Ar flow ratio of 16:1 at a substrate temperature of 250°C. The films show an activated-type conduction (with an activation energy of 0.36 eV) and a hydrogen concentration of about 11 at.%. The IR spectra reveal absorption bands corresponding to both monohydride (Ge-H) and dihydride (GeH2) groups. The monohydride absorption band is, however, completely absent in films deposited at 350°C for the same H2:Ar flow ratio. X-ray diffraction analysis shows that these films are microcrystalline and show an enhanced electrical conductivity (4.0×10-3ω-1cm-1) with decreased activation energy (0.29 eV).

Screen-printed thick films of the ceramic oxide superconductor material YBa 2 Cu 3 O 7 − x have been prepared on alumina substrates. A buffer layer of glass between the substrate and the oxide film has been used to promote adhesion as well as to decrease the reaction between the substrate and the film and thus to prevent “poisoning” of the superconducting thick film. Structural and electrical properties of the thick films have been studied. The sintered films show an orthorhombic structure with columnar growth with an oriented c axis. The films exhibit onset of superconductivity at 82 K with a 2 K transition width and a critical current density of 100 A cm −1 at 77 K.

The addition of nearly 11 at.% Bi to amorphous Ge20Se70 films results in an increase in the room temperature conductivity by several orders of magnitude, a transition from p- to n-type conduction, a decrease in the optical gap from 1.85 to 1.15 eV, and a large decrease in the electrical activation energy from 0.82 to 0.09 eV. The optical and electrical data suggest that the addition of bismuth produces localized states near the conduction band edge so that the electrical transport is due to the hopping of electrons after being excited into localized states at the conduction band edge.

The surface metallurgy of several commercially available cemented carbide tools was studied by Auger electron spectroscopy and X-ray photoelectron spectroscopy techniques. The tool surfaces were contaminated by adsorbed oxygen up to a depth of nearly 0.3 μm causing deterioration of the mechanical properties of the tools. Studies of fractured samples indicated that the tool surfaces were prone to oxygen adsorption. The fracture path passes through the cobalt-rich regions. The ineffectiveness of a worn cutting tool is attributed to the presence of excessive iron from the steel workpiece and carbon and oxygen in the surface layers of the tool. The use of appropriate hard coatings on cemented carbide tools is suggested.

Hydrpgenated amorphous germanium-carbon (a-Ge1−xCx:H) thin films have been prepared by an Activated Reactive Evaporation (ARE) technique. Germanium was evaporated from a resistively heated tungsten basket through an acetylene plasma. The films thus obtained were characterized for the compositional, structural, electrical and optical properties. The effects of substrate temperature, role of hydrogen and variation of optical energy gap with carbon content were also investigated. Typically, films deposited at 200 °C showed a sharp absorption edge corresponding to an optical gap of about 1.3 eV and thermally activated electrical conduction over a wide range of temperatures.

Hollow crystals of ZnO, in the shape of needles, have been grown for the first time using a modified vapor phase technique. The technique already in use for the growth of ZnO crystals has been modified by making Zn and hence ZnO vapor available at the growth temperature itself and in the same reaction zone where the growth actually takes place. The hollow needles up to 10 mm in length and 1 mm in diameter have been observed to grow on the ZnO substrate. The growth of these crystals has been attributed to the condensation of ZnO vapors, which are formed by the spontaneous oxidation of Zn vapors coming out from the hole of the growing crystal.