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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.

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.

Functionally graded tungsten–copper bimetallic compact with fine microstructure and good mechanical property has been synthesized by employing microwave heating method at a temperature of 800 °C and in a short processing time of 30 min. Scanning electron microscopy and energy dispersive X-ray analysis revealed the graded structure of synthesized sample. The fine microstructure of tungsten in each layer is caused by arrested grain growth because of the short sintering time. The overall relative density of the W/Cu functionally graded sample has reached 87% of the theoretical density. Vickers microhardness measurements, across the length of a compact, show increase in hardness value of the sample with the increase in tungsten content. The experimental hardness values match well with the theoretically calculated hardness values.

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.

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.

Observation of room temperature ferromagnetism (RTFM) is reported in polycrystalline thin films of Ti1−xMnxO2 (x = 0.10 and 0.15) synthesized by spray pyrolysis technique on fused quartz substrates. Our experimental results clearly suggest partial incorporation of manganese (Mn) in titanium dioxide (TiO2) lattice up to certain extent and rest of the Mn ions are consumed to form secondary Mn-related phase such as manganese oxide (Mn3O4). The observed weak ferromagnetic ordering at room temperature in the films is established to be due to incorporation of Mn in TiO2matrix rather than the presence of other secondary phases since none of the Mn or Ti/Mn oxide phase is ferromagnetic at room temperature. Bound magnetic polaron model is invoked to explain the observed ferromagnetism in these highly resistive films.

Observation of room temperature ferromagnetism (RTFM) in nano-crystalline Co-incorporated titanium dioxide [Ti(1-x)Co(x)O2(x = 0.05)] thin films prepared by spray pyrolysis technique is reported. While only the anatase phase was detected in as-deposited 5 at.% Co-incorporated TiO2 film, a small amount of rutile phase developed following its vacuum annealing. Besides, no X-ray diffraction peak corresponding to cobalt metal could be detected in any of the two films. SQUID magnetometry of both pristine and Co-doped thin films at room temperature elucidated distinct ferromagnetic behavior in 5 at.% Co-incorporated as-deposited film with saturation moment M(s) approximately 5.6 emu/cm3 which got enhanced up to 11.8 emu/cm3 on subsequent vacuum annealing. From the zero field cooled magnetization measurement we confirmed the absence of Co-metal clusters. The electrical resistivity was found to be greater than 108 omega-cm for the films. Based on the magnetic and electrical measurements the origin of RTFM has been attributed to the bound magnetic polaron (BMP) model.

Nanocrystalline samples of both undoped TiO2 and with 5 at.% Co at cationic sites were prepared by a simple chemical route. X-ray diffraction study of these samples revealed an increase in lattice parameters due to incorporation of Co in the TiO2 lattice and possibly due to formation of oxygen vacancies. No traces of crystalline Co or any other secondary phases could be detected. High-temperature SQUID measurement of these samples exhibited ferromagnetic signature up to 700 K, implying that the Curie temperature of doped and undoped TiO2 exceeds 700 K. Vacuum annealing of both types of samples enhanced the ferromagnetic character. The as-prepared and vacuum-annealed Co incorporated TiO2 samples, in addition to the ferromagnetic character, also exhibited a paramagnetic signal. All these measurements strongly support the role of defects in inducing room-temperature ferromagnetism in undoped and Co doped TiO2 nanopowders, which can be explained using the bound magnetic polaron model.

NiCuZn ferrite nanopowders and polycrystalline bulk samples were prepared by wet chemical (citrate) method followed by sintering at temperatures lower than those for conventional solid-state ceramic route. The citrate method results in nano-powders. The addition of copper promotes sintering, and results in grain-growth during sintering, even at a low temperature. Composite thick films of desired thickness were prepared by die casting the ferrite mixed with a polymer in different weight ratios. The dielectric properties of the polycrystalline NiCuZn ferrite and their composite thick films were investigated at radio- and X-band microwave frequencies. Dielectric and magnetic losses are estimated to be appreciably low, even at microwave frequencies.

In the present work, silicon nanowires have been grown in a TE011 single-mode cylindrical microwave resonant cavity operating at 2.45 GHz. The microstructural, structural, elemental, and room temperature photoluminiscence studies have been carried out of the grown nanowires. The wires are encapsulated by an ultrathin layer of silicon oxynitride. The observed strong visile photoluminescenc is ascribed to ballistic transport and radiative recombination (at Si/SiON interface) of the carriers generated due to light absorption.

The present paper describes Raman studies of chemically synthesized nanocrystalline cobalt-substituted (up to 10%) ZnO samples exhibiting room temperature ferromagnetism. These studies were carried out using Laser excitation wavelengths −457.9, 532 and 785 nm. The Raman spectra of the samples excited with 457.9 nm show predominantly lattice modes of ZnO because of pre-resonance enhancement. In the Raman spectra of cobalt added ZnO samples excited with 532 and 785 nm, clear evidence is seen for the presence of Co3O4 (an impurity phase not detectable in XRD) in the samples with cobalt exceeding 3%. The presence of Co3O4 in the samples having higher concentration of cobalt explains the nonmonotonic increase in magnetization with Co-concentration in the ZnO1 − xCox samples.

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.

Preparation of barium hexaferrite nanoparticles by chemical route and investigations of their dielectric and magnetic properties at microwave frequencies (8–12 GHz) are reported in the present paper. Measurements of these properties were carried out at microwave frequencies by using a cavity perturbation technique. It is observed that the values of the permittivity and permeability of nanoparticles are lower than the corresponding values for the bulk material. The effects of particle size, calcination temperature and compositional dependence on structural, microstructural and magnetic properties are also discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We measured dielectric, magnetic, and microwave properties of Co 2U hexaferrite (Ba4Co2Fe36O 60) polycrystalline bulk and composite thick film samples, and studied the effect of annealing temperature on phase formation and microstructure. We synthesized the bulk samples from a precursor prepared by the citrate method. The values of dielectric constant at radio frequencies (50 Hz-1 MHz) of the bulk Co2U12 sample sintered at 1200degC are much higher, and the resistivities are lower, compared to M-type barium hexaferrites. Coercivity is also low, having a value of 5 G for the Co2U12 sample, whereas the saturation magnetization value is 59 emu/g, which is comparable to that of M-type hexaferrites. We also measured the complex permittivity and permeability for Co2U12 samples at microwave frequencies and found the values high compared to M-type barium hexaferrite at these frequencies. Thick composite films were prepared from a ferrite-polymer mix, and all the above properties were studied for these films. We observed that these thick films have lower values of dielectric and magnetic parameters both at low and microwave frequencies. We measured microwave-absorbing properties for the ferrite-polymer sample (ferrite to polymer ratio 70/30) which showed a maximum reflection loss of -37.5 dB at 11.5 GHz for the 3.5-mm-thick sample

Co/Cu multilayers were electrodeposited in potentiostatic mode, using two different sulphate baths, one without any additive and other containing trisodium citrate. Deposition parameters, like deposition potential and deposition time, were established for both the baths by carrying out a series of cyclic voltammetry and chronoamperometric experiments. Thin films, having 2–20 bilayers, were electrodeposited under the established parameters. It was observed that films deposited from bath containing trisodium citrate were comparatively much smoother than films deposited from additive free bath. The films with 20 bilayers, deposited from additive free bath, exhibited a room temperature magnetoresistance of 1.5% at 9 kG, whereas magnetoresistance value enhanced to up to 5.6% at 9 kG for films deposited from trisodium citrate bath for same number of bilayers.

NiCuZn ferrite has recently attracted a lot of attention for its application in high frequency (up to a few GHz) multilayer chip inductors (MLCIs) and for other microwave devices owing to their favorable electromagnetic properties and low densification temperature. In order to study the effect of substitution of cations by cobalt in small concentration on the dielectric and magnetic properties at low and high frequencies, bulk polycrystalline ferrite samples of starting composition (Ni0.2Cu0.2Zn0.6)1 − x Co x Fe2O4, having x = 0, 0.01, 0.03 and 0.05, were prepared by citrate precursor method. Pure spinel (cubic) ferrite formation was confirmed by powder X-ray diffraction technique. Complex permittivity and permeability were measured at microwave frequencies (X-band) using the cavity perturbation method, which is a non-contact method. The values of real part of permittivity (e ′) vary in the range 7–9.6 and of the imaginary part (e ″) vary from 0.020–0.120, whereas real part of the permeability (μ′) lies in the range 2.6–14.0 and the imaginary part of permeability (μ″) varies from 0.5–6.0. It is observed that there is an increase in μ′ and decrease in the magnetic loss (tan δ μ) on increasing the cobalt concentration from x = 0 to x = 0.05. The variation of these parameters, both with frequency in X-band and with the cobalt concentration, is discussed in this paper.

Superconducting bulk MgB2 samples have been synthesized by employing sintering technique without using any additional process steps, generally undertaken in view of the substantial loss of magnesium, during heat treatment. Starting with Mg rich powders having different atomic ratios of Mg : B, as against the nominally required Mg : B = 1:2 ratio, we have obtained superconducting MgB2 samples of different characteristics. The effect of excess Mg in the starting mixture and processing temperature on the phase-formation, transition temperature (T C) and critical current density (J C) have been investigated by electrical transport and a.c. susceptibility measurements. The X-ray diffraction and X-ray photoelectron spectroscopic analyses of MgB2 bulk samples have been carried out to understand the role of excess Mg and the effect of processing temperature. It is established that MgB2 samples with high critical current density can be synthesized from a Mg rich powder having Mg : B in 2:2 ratio, at temperatures around 790°C. Critical current density has been found to vary systematically with processing temperature.

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.

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.

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.

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 .

Epitaxial thin films of YBa2Cu3O7-δ, prepared by the low-pressure rf-magnetron sputtering technique, have been irradiated with 100 MeV 58Ni ions at a dose exceeding 1012 ions cm−2 at 77 K. Low-field magnetic ac-susceptibility measurements (X ac −T ) are performed before and after the irradiation to study the irradiation-induced effects in the films. A superconducting transition accompanied by an anomalous change in the X ac −T response. that is a positive susceptibility peak just below the transition temperature, is seen for the first time in the ion-irradiated films. This ion-irradiation-induced positive-susceptibility trait has been attributed to the paramagnetic Meissner effect. It is proposed that the ion irradiation at higher fluences leads to the formation of a π junction through the partial removal of oxygen ions in the chain sites and results in the observed extrinsic paramagnetic Meissner effect.

In the present paper, a modified self-flux technique has been successfully employed for the growth of pure and praseodymium substituted (partially) large single crystals of high temperature superconducting Y1−x Pr x Ba2Cu3O7−δ (x = 0·0,0·2,0·4). Typical sizes of the platy and bulky crystals of pure YBCO(123) material are ≈ 2 × 2 × 0·1 mm3 and 4 × 1 × 1 mm3, respectively. In case of Pr-substitution, the typical sizes of platy and bulky crystals of Y0·8Pr0·2Ba2Cu3O7−δ and Y0·6Pr0·4Ba2Cu3O7−δ materials are ≈ 2 × 3 × 0·1 mm3 and 5 × 1 × 1 mm3 and ≈ 1 × 1·5 × 0·1 mm3 and 7 × 0·2 × 0·1 mm3, respectively. The morphology and growth habit of the as-grown single crystals and the critical transition temperature (T c) of the oxygenated crystals were found to depend on the Pr-content.

Bismuth germanium oxide (BGO) has tremendous application potential due to its favourable electro-mechanical and electro-optic properties. The present paper describes some of our preliminary results on the variation of dielectric constant with applied high hydrostatic pressure and temperature. It is noted that BGO is a promising candidate for its application as a pressure sensor.

Very thin fluorine-doped tin oxide films (60–70 nm) were prepared on glass substrates at low deposition temperatures (275–300°C), these films showed an electrical resistivity of 3.2 ×10-4Ω-cm and a transparency of 88% at 625 nm with the application of a dc electric field on the film surface during growth using a spray pyrolysis deposition technique. In this first study of its kind, the applied electric field during growth by spray pyrolysis resulted in the reduction in the critical thickness and the increases in both the electrical conductivity and transparency of continuous films. The obtained X-ray diffraction (XRD) patterns showed that the films prepared with an electric field were polycrystalline, whereas those prepared without an electric field were amorphous. This method shows potential for producing very thin oxide films at a low deposition temperature with a high growth rate, an enhanced optical quality and an improved electrical conductivity.

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.

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.

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.

Studies on Mn, Ni and Co doped ZnO systems have revealed that the RTFM present in these systems can be both intrinsic and extrinsic depending on the choice of TM ion incorporated, technique of preparation and post-synthesis processing. Choice of such a technique that ensures better homogeneity and incorporation of TM ions in the ZnO host, leads to the occurrence of intrinsic, stable and robust RTFM. The air ambient processing eliminates the chances of any metallic cluster inclusions, and instead such TM oxide phases are formed that are non-ferromagnetic. However, post synthesis processing like vacuum annealing of ZnO:Co samples under some situations can give rise to occurrence of extrinsic RTFM. But, this can be overcome by certain additional processing step. ZnO:Co samples with intrinsic RTFM, stable upto 900°C annealing with Curie temperatures in excess of 450°C have successfully been prepared.

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.

The charged state of bismuth atoms in n‐type bismuth‐modified amorphous thin films of Ge20Se80 and As2Se3 has been studied by x‐ray photoelectron spectroscopy. On the basis of the observed chemical shift, it is concluded that the Bi atoms in the modified films are positively charged. The charged Bi atoms perturb the equilibrium between positively and negatively charged defect centers, thereby causing a shift of the Fermi level towards the conduction band. The observed enhanced electrical conductivity and the conductivity conversion from p to n type in the modified films is the result of such a Fermi level shift.

We report here the room temperature ferromagnetic ordering in spray-pyrolized polycrystalline thin films of Ti1−xCoxO2 (x = 0, 0.025, 0.05 and 0.10). The saturation magnetic moment in these films with x = 0.05 and 0.10 is estimated to be of 0.28 and 0.38µB/Co, respectively. The ambient air employed in the present case of the spray pyrolysis process resulted in ferromagnetic films possessing very high resistivity values (∼10 7 � cm). This is in contrast to Ti1−xCoxO2 films deposited by vacuum based techniques, which are relatively conducting. While pristine TiO2 film exhibited the anatase phase, the rutile phase of TiO2 also evolved with an increase in Co concentration in these films. X-ray diffractograms could not reveal segregation of Co atoms in the TiO2 matrix; also, no formation of any oxide of cobalt was detected. X-ray photoelectron spectroscopic investigation established the Co cations to be bivalent, and suggests that Co +2 is substituting Ti +4 in the TiO2 matrix. Due to the highly resistive nature of these films, the observed room temperature ferromagnetism could be attributed either to the formation of bound magnetic polarons or to defect mediated ordering.

The high temperature magnetization behavior of an air sintered nanocrystalline ZnO:Co (5at.%) sample while it is subjected to thermal cycles in vacuum/air ambient is reported in the present paper. The pristine air sintered sample exhibits intrinsic room temperature ferromagnetism. Upon vacuum annealing, the magnetization of this sample increases significantly and the sample remains ferromagnetic up to 630°C. This has been attributed to the formation of Co clusters, and thus, the ferromagnetic ordering is extrinsic in nature. The subsequent air annealing of the vacuum annealed ZnO:Co (5at.%) sample, however, reverts back the magnetization to a value that was observed in the pristine air sintered sample. This is due to complete oxidation of the cobalt clusters. Furthermore, the sample’s magnetization at room temperature and also its temperature dependence up to 630°C remain unaffected by further annealing in vacuum or air, a feature required of a material for its device applications. The Curie temperature o...

High temperature magnetization studies (up to 650°C) of the chemically synthesized nanocrystalline Zn0.9Co0.1O samples are reported in this paper. A systematic study of sequentially sintered sample has been carried out to correlate the observed changes in magnetic behavior vis a vis very small changes in the unit-cell dimensions, evolution of cobalt oxide phases, and absence of Co clusters. The Curie temperature of cobalt substituted ZnO is determined to be ∼495°C. A plausible explanation of the observed room temperature ferromagnetism is presented in terms of bound magnetic polarons model.

Optical properties of spray pyrolysed Sn1?xCoxO2?? (0?x?0.15) thin films exhibiting room temperature ferromagnetism have been investigated in the energy range 1?6?eV. The onset of optical absorption is blueshifted by as much as 220?meV for a cobalt concentration of 10a/o (x = 0.10). Our detailed analysis indicates that the most probable cause of the blueshift is the Burstein?Moss effect. The optical conductivity calculations reveal that Co does not introduce any mid-gap states. Also the small change in the slope of ?2 versus h? indicates that the O and Sn band edges are affected on Co addition. This band-edge shift also implies the presence of strong Coulomb interaction between Co, Sn and O sites, as a plausible cause of the observed ferromagnetism in these samples. The Burstein?Moss effect seems to be masking the effect of band structure modification introduced by Co addition. The high (~75%) optical transparency of these films in the visible region remains practically unaffected on Co addition.

A maximum room temperature ferromagnetic moment of 0.47μB∕Co ion has been observed in Sn0.9Co0.1O2−δ films grown by spray pyrolysis. The films have high conductivity (∼150Ω−1cm−1) and ∼70% transmittance in the visible region. A systematic variation of saturation magnetization, carrier concentration, electrical conductivity, and optical transmission edge in Sn1−xCoxO2−δ(0.05⩽x⩽0.15) films is correlated with the change in Co concentration, and a carrier mediated Ruderman-Kittel-Kasuya-Yoshida interaction has been proposed as the most probable mechanism for the ferromagnetic ordering. The maximum blueshift in the transmission edge by ∼215meV (at x=0.10) is attributed to the extra carriers generated by Co substitution.

Thin films of Cu-Co alloy exhibiting excellent metallic luster were galvanostatically electrodeposited directly on Si substrates in a single citrate bath containing sulfates of the metal ions. The direct electrodeposition onto n-Si substrates eliminated a processing step, of depositing a conducting layer, if an insulator were to be used as a substrate. In addition, the use of silicon as a substrate is promising in integrating this inexpensive technique with semiconductor microelectronic device fabrication technology. The as-deposited films exhibited giant magnetoresistance (GMR) of 1% (T = 300 K, H = 10 kOe) and 5% (T = 10 K and H = 50 kOe). The annealed films showed an increase in GMR from I to 2.7%. The X-ray diffraction studies of as-deposited metastable films indicate solid solution like behavior following Vegard's law. However, our magnetic studies evidenced the presence of very fine nanograins of Co in these films. A systematic study of the effect of various processing parameters like deposition current density, bath temperature, and pH on the composition, structure, and microstructure of thin films was carried out to understand the electrodeposition process. Deposition current density and bath temperature have significant control over the composition and microstructure. The pH of the electrolyte seems to affect the topography most. Like physical vapor deposition (PVD), the electrodeposition process yields thin films via a nucleation-controlled growth mechanism. The superiority of the electrodeposition technique over the PVD technique is emphasized.

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).

Electrical, optical, and structural 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. A detailed description of the deposition setup, preparation procedures, and techniques of property measurement is given. The dependencies on beam voltage, H2:Ar flow ratio, and substrate temperature of the room‐temperature dark conductivity, optical band gap, hydrogen content, and ellipsometric and IR data are reported and analyzed. The minimum conductivity (10−4 Ω−1 cm−1) a‐Ge:H films have been obtained for H2:Ar flow ratio of 16:1, and beam voltage and substrate temperature of 1000 V and 250 °C, respectively. These films contain a hydrogen concentration of about 11 at. % and show an optical band gap near 1.04 eV. The IR spectra reveal absorption bands corresponding to both monohydride (Ge‐H) and dihydride (GeH2) groups for all the samples deposited. The monohydride ab...

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.

Amorphous thin 6lms of Ge20Bi4Se76 exhibiting n-type conduction are reported for the first time. As compared to a-Ge20Se80 films, the modified films (a-Ge20Bi4Se76) show an increase in room-temperature electrical conductivity by several orders of magnitude, a transition from p-to n-type conduction, a decrease in the optical gap from 1.9 to 1.5 eV and a drastic fall in the electrical activation energy from 0.85 to 0.17eV. The correlation of the electrical and optical data suggests the existence of localized states at the conduction band edge arising from the incorporation of bismuth. The decrease of the activation energy for electrical conduction is much larger than the decrease of one-half the optical gap. This indicates unpinning of the Fermi level with a shift towards the conduction band edge.

Thin films of hydrogenated amorphous silicon‐germanium (a‐Si1−xGex: H) alloys have been prepared by reactive ion beam sputtering of a composite target of silicon and germanium. The dependence of the deposition rate, conductivity‐temperature variation, optical absorption coefficient, refractive index, imaginary part of the dielectric constant, hydrogen content, and infrared (IR) absorption spectra on germanium content (x) are reported and analyzed. For a typical composition—a‐Si28Ge72:H (x=0.72), the effect of beam voltage, H2:Ar flow ratio, and substrate temperature on the material properties have also been investigated. For the films prepared with increasing x, the expected behavior of a decrease in both hydrogen content and band gap and an increase in the electrical conductivity have been observed. The films prepared at x>0.80 are found to be more homogeneous than the films deposited at 0.0

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.