Search

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.

Polycrystalline samples of Ni1 − xCoxFe2O4 (where x = 0.0, 0.4, 0.5, 0.6, 1.0) have been synthesized by solid state sintering of stoichiometric nanoparticles prepared by sol–gel technique. Rietveld refined powder X-ray diffraction patterns confirm the formation of a single cubic spinel phase in each sample. Substitution of cobalt ions results in the increase of the lattice parameter. The saturation magnetization and coercivity of all the samples were measured using PPMS-VSM and found to increase from 51.6 to 82.2 emu/g, and 9.7 to 588 Oe, respectively. The observed magnetic ordering is explained on the bases of two sublattice model and redistribution of cations in these partially inverse Co substituted Ni ferrite samples. The strong increment (60 times) in the coercivity is explained on the bases of microstructure and magnetocrystalline anisotropy. Cation redistribution in these samples is proposed on the basis of the observed magnetic moment. Close matching of lattice parameter calculated from the magnetic data and estimated from the X-ray diffraction data supports the proposed cation redistribution in the partially inverse spinel phase of NCFO.

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.

Background: Psychiatric morbidity in psoriasis is influenced by socio-cultural factors. Most of the studies in this perspective are done in western setup; to extrapolate them on Indian patients with different demographic and socio-cultural profile may not be appropriate. Our study was designed to evaluate the prevalence and its correlation to various socio-economic variables in Indian patients. Methods: This was a non-interventional, cross-sectional study, in which 125 consecutive psoriasis patients over one year were screened for psychiatric morbidity. Demographic and disease parameters including Psoriasis Area and Severity Index (PASI), Psoriasis Disability Index (PDI), General Health Questionnaire (GHQ), Comprehensive Psychopathological Rating Scale (CPRS) were recorded along with the severity assessment of psychiatric morbidity and its relation to these variables was analyzed. Results: Among 125 psoriasis patients, 43 (35.2%) had psychiatric morbidity. Thirty two (26.4%) had depression, 3 (2.4%) had dysthymia, generalized anxiety disorder and adjustment disorder each, and 2 (1.6%) suffered social phobia. A significant increase in psychiatric morbidity was seen with increase in PDI and PASI scores. Conclusions: There is a significant psychiatric morbidity associated with psoriasis and it increases with severity of the disease.

Background: Body art in the form of ornamental tattoos has been prevalent since ages and is followed with increased popularity in modern times. Tattoo prevalence ranges from 8.5% to 24%, higher among younger ages. Two third of such people who ever had a tattoo reported of being regretted of having a tattoo itself while 2% have adverse reactions. The aim was to study the adverse reaction to tattoos and histological variants in the chronic tattoos. Methods: An observational prospective study was conducted on patients presented with adverse reactions to tattoos in the out-patient department of dermatology, venereology and leprosy, Indira Gandhi Medical College, Shimla, Himachal Pradesh, India from July 2012 to June 2013. Relevant clinical profile of the patient was studied and histopathological examination with a 5 mm punch biopsy was done in chronic cases. Results: A total of thirty-three cases (19 male and 14 females) with complications to tattoos were registered over the period of one year. Thirty patients had their tattoo from an amateur while only three had from a professional tattooist. Twenty one (63.6%) had acute complications and twelve (36.3%) had chronic complications. Histpathological examination (HPE) was done in ten of these cases and two refused biopsy. The findings were suggestive of lupus vulgaris (LV) and foreign body granuloma (FBG) in three each; chronic granulomatous changes in two, and spongiotic dermatitis (SD), and lichen planus hypertrophicus (LPH) in one case each. Conclusions: Tattooing being largely unregulated has led to variability in contents of tattoo solution and inadequate sterilization during the procedure. This combined with lack of awareness, increases the chances of various adverse reactions. So it is extremely important to strictly regularize the tattoo practice and to increase awareness about tattoo complications among consumers, tattoo artists and dermatologists.

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.

During the last few decades, democracy, as the most preferred form of government, has been repeatedly revisited. Considerable literature has grown up round the concepts of inclusive governance and social responsibility as essential elements of democracy. Besides the learned scholars, some international organizations such as the World Bank, the World Health Organization and the United Nations Development Programme have become involved in this discussion. In the so-called developing world of South Asia and Africa, the fruits of freedom, rule of law and economic growth have been cornered by the few and not shared by all. The worst sufferers have been the most deprived and marginalized sections: women, tribals, people with disabilities, ethnic, religious or other minorities, the aged, social outcasts and the poor and least developed. For the debate on inclusive government and socially accountable democracy to be meaningful to ordinary citizens, the first categorical imperative is to shear it of much of its jargon. Democracy today is believed to be a system under which the people govern themselves, through the representatives they elect, under a system they choose. Yet representative democracy must graduate to participatory democracy, where the people are conscious of their rights and obligations, assume responsibilities and partake in decision-making processes. Furthermore, democracy has to be inclusive of the interests of all, equally and without discrimination. Special attention has to be paid to the disadvantaged and deprived. Good governance has to be democratic, citizen-friendly, clean and free of corruption. All the state functionaries, at all times, must be answerable and accountable to the ultimate masters in democracy: the people. Inclusive governance requires decentralization of power, equal participation of the people, equality of all before law and real empowerment of the people, with a bottom-up approach.

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.

Single-phase nanoparticles of Mn0.5Zn0.5Fe2 O 4 (MZF) with improved magnetic properties were prepared from the precursor (formed by chemical route) by microwave processing technique at 500 ∘C in only 3 min. Crystallographically, these were found to be of spinel phase. Using Debye-Scherrer formula, the particle size of conventionally sintered powder is estimated to be about 20 nm, whereas that of microwave processed is nearly 50 nm with improved grain size. The field emission scanning electron (FESEM) and transmission electron (TEM) micrographs revealed the particles in microwave-processed samples to be spherical in shape and confirmed the sample size (to be nearly 50 nm). Room temperature magnetization measurement of conventionally sintered samples (by vibrating sample magnetometer (VSM)) showed their superparamagnetic nature with saturation magnetization of nearly 19 emu/g. The microwave-processed samples showed improved saturation magnetization of nearly 36 emu/g, which is even better than the reported value.

Measurement of electrical and magnetic parameters of thin/thick films at microwave frequencies has always been challenging. This is because the measurement of permittivity and permeability of the films in GHz range is not as straight forward as of the bulk samples. The present paper reviews some of the available techniques with emphasis on the efforts carried out in authors’ laboratory in this direction during past 10–15 years.

The basal cell carcinoma is the most common skin tumour especially affecting the white individuals worldwide. The exact incidence of basal cell carcinoma is not known from India but non melanoma skin cancers comprises about 1-2% of cutaneous tumour in India. The most common skin tumour is squamous cell carcinoma in albinism and the incidence of basal cell carcinoma is less. Hereby, we report a peculiar case of basal cell carcinoma in albinism to highlights the importance of early recognition and diagnosis of suspected lesions by performing histopathological examination in unusual circumstances.

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.

The present study was carried out in Kashmir (India) to assess the genetic variability for grain yield and component traits among 14 red rice ecotypes from temperate region (locally known as Zag for its coloured kernels) and correlation and path coefficients were also studied for fifteen agro-morphological characters. Genotypic and phenotypic coefficients of variation were high for grain yield, secondary branches per panicle and panicle weight; moderate for grain number per panicle, grain length:breadth (L:B) ratio and panicle density. High heritability accompanied by high to moderate genetic advance for panicle density, days to 50% flowering, plant height, grain number indicated the predominance of additive gene action for the expression of these characters. Grain yield was found to be positively and significantly correlated with number of tiller per plant, panicle density m-2 and number of grain per panicle at both genotypic and phenotypic levels indicating the importance of these characters for yield improvement in this material. The results of genotypic path analysis revealed that panicle density had the highest positive direct effect followed by plant height and days to flower. The overall results indicated that selection favouring higher panicle density, test weight and panicle weight and medium plant height with a reasonable balance for moderate grain number would help to achieve higher grain yield in this population of red rice ecotypes.

The Mn0.5Zn0.5Fe2O4 nanoparticles has been synthesized using citrate-gel-precursor method. The direct mixing of nitrates and acetates yields homogeneous nanoparticles. Phase formation and crystal structure of the synthesized powder were examined through the X-ray diffraction (XRD). Fourier transform infrared (FTIR) spectra of the sample confirm the spinel structure. The average particle size was determined by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The average particle size is found to be about 13 nm. Superparamagnetic-like nature of the nanoparticles of Mn0.5Zn0.5Fe2O4 has been revealed through various dc and linear and non-linear ac magnetization measurements. However, the nanoparticles do not behave like ideal non-interacting superparamagnets. The magnetic particle size is found to be about 8 nm with saturation magnetization about 18.1 emu/g. The blocking temperature (T(B)) of the nanoparticle assembly is found to be about 150 K as observed from dc and ac magnetization measurements. The frequency dependence of the blocking temperature (T(B)) is found to follow Vogel-Fulcher law. The associated characteristic time tau0 is found to be 10(-5) s. This value is different from that generally found for non-interacting superparamagnetic (SPM) systems (tau0 = 10(-9)-10(-10) s).

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.

/CoFe/IrMn/CoFeB trilayers without any “eld cooling protocol. Theappearance of positive exchange bias is attributed to the antiferromagnetic coupling between theuncompensated Mn and ferromagnetic (FM) CoFeB spins at the interface. PEB in our sample isobtained as a consequence of interfacial microstructure control leading to unidirectional exchangeanisotropy, brought about by the incident energetic atoms/ions produced during ion-beam sputter-ing. On magnetic annealing, enhancement in the coercivity and disappearance of exchange bias isobserved irrespective of IrMn (111) textured growth due to the irreversible changes in the interfacialspin structure. The coercivity of CoFeB layers can be tuned by varying the seed layer thickness inthe magnetically annealed samples. The signi“cance of this work is a new insight into the effectof incident energetic atomic ”ux on the interfacial microstructure leading to positive exchange bias.Moreover, this study is promising in paving way for the utilization of trilayer stack with independentlyswitchable FM layers in CoFeB based TMR and GMR structures.

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.

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.

The present paper describes our results on the phase transformation (from crystalline to amorphous) of M-type hard barium hexaferrite, and consequently its conversion into soft ferrite by the application of magnetic energy at microwave frequency (2.45 GHz). The rapid volumetric heating of the conventionally prepared polycrystalline hexaferrite by microwave energy at a temperature of 950 °C in a short duration of only 5 min resulted in a decrystallized phase. The magnetic studies (M–H loops) of the resistively heated and MW processed samples have revealed a lowering in coercivity (from 188 to 2 mT) in the latter samples, thereby establishing the formation of soft ferrite. An attempt has also been made to understand the observed transformation from hard to soft ferrite.

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.

Thin films and nanowires of Fe3O4 have potentiostatically been electrodeposited on ITO coated glass and employing templates in a conventional three-electrode cell using two different baths. Appropriate potential windows, suitable for films and nanowires, were estimated from cyclic voltametry. Structural property of Fe3O4 films was studied by X-ray diffraction. A large (−3.35%, at 2.3 kOe) longitudinal magnetoresistance (MR) was observed at room temperature, and the shape of MR curves showed a reduced hysteresis loop for Fe3O4 films with low coercivity. Room-temperature magnetic properties of Fe3O4 films were studied by vibrating sample magnetometer (VSM). Surface morphology of nanowires was studied by scanning electron microscope (SEM). The nonlinear I–V characteristic of nanowires was observed at room temperature. An attempt has been made to understand the conduction mechanism.

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 ZnTi substituted barium hexaferrite polycrystalline samples have been synthesized by solid-state reaction method. The complex permittivity and permeability measurements are carried out on the BaFe12–2xZnxTixO19 (0.2 ≤ x ≤ 0.6) samples in the microwave frequency range of 8–13 GHz by cavity perturbation technique. The observed abnormal dielectric behavior, i.e., an increasing tendency of dielectric constant with frequency has been attributed to the mixed conduction. The effect of ZnTi substitution on the permittivity and dielectric loss has been investigated in the frequency range of 1 kHz–1 MHz as well. The increase in concentration of ZnTi dopants monotonically increases both the permittivity and the permeability in the investigated frequency ranges, which can be attributed to increased polarizability and unpinning of the domain walls, respectively.

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.

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.

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)

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).

Cobalt-substituted lithium ferrites (with general composition Li0.5–x /2CoxFe2.5–x /2O4, where x = 0.0, 0.2, 0.4, 0.5 and 0.6) were prepared at lower processing temperatures (∼600 °C) by the citrate route. The single-phase spinel structure was confirmed by X-ray diffraction. The average particle size of calcined powders calculated by the Scherrer formula is estimated to be 8–90 nm, whereas an average particle size of ∼20 nm is observed from TEM for Co concentration x = 0.5. Average grain sizes from SEM micrographs of pellets sintered at 1000 °C (1 h) are observed to be 0.5–1 μm, much smaller than the size reported for the standard ceramic method (2.1–6.8 μm). The experimental density is observed to be 3.59–4.47 gm/cm3, which is greater than 85% of the densities evaluated from XRD. Compared with the standard ceramic method, lower dielectric constant (10–103) and higher dc resistivity (105–1010 Ω cm) is observed for Li–Co ferrites prepared by the citrate route. Improved magnetic properties, such as higher saturation magnetization (38–79 emu g–1) and Curie temperature (535 to 620 °C) are also investigated for the citrate-route-processed samples. These results demonstrate promising features of Li–Co ferrites in microwave applications. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nano-multilayers of Cu(6 nm)/Co(∼22 nm) have been electrodeposited in potentiostatic pulse mode on ITO coated glass substrates. Cyclic voltammetry and chronoamperometric studies were performed to determine the potential and duration for the deposition of individual layers. A 50-bilayer stack exhibited a room temperature GMR of 12.5%, at 8 kOe. Even at low fields of ∼3 kOe, this multilayer exhibited ∼10% GMR, thereby demonstrating the potential application of electrodeposition (ED) process in achieving appreciable value of GMR at room temperature and at lower field values. The observed high value of GMR at room temperature may be attributed to the antiferromagnetically (AF) aligned magnetic layers in the absence of magnetic field. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)