Subhash Kashyap

Subhash Kashyap
Indian Institute of Technology Delhi | IIT Delhi · Department of Physics

M.Sc.,BITS Pilani; Ph.D., IITD

About

175
Publications
10,461
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
2,231
Citations
Additional affiliations
April 1978 - June 2014
Indian Institute of Technology Delhi
Position
  • Faculty Member
Description
  • Joined IITDelhi as a lecturer in 1978; and retired as a professor in 2014.
April 1978 - June 2014
Indian Institute of Technology Delhi
Position
  • Professor Emeritus
January 1973 - December 2013
Indian Institute of Technology Delhi

Publications

Publications (175)
Article
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,...
Article
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 for...
Article
Polycrystalline Zn–]Zr substituted barium hexaferrite (BaFe 12-x Zn x/2 Zr x/2 O 19 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 di...
Article
Full-text available
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 th...
Article
In the present paper an attempt has been made to understand the growth mechanism of SiGe alloy nanowires synthesised in H-mode cylindrical microwave cavity resonator at 900 °C in a short time of nearly 5 minutes. The role of ambience, microwave H-field, duration of interaction with microwaves and germanium concentration in the starting precursor ha...
Article
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 estab...
Article
A series of Mn-Zn Ferrite nanoparticles (<15 nm) with formula MnxZn1−xFe2O4 (where x=0.00, 0.35, 0.50, 0.65) were successfully prepared by citrate-gel method at low temperature (400 °C). X-ray diffraction analysis confirmed the formation of single cubic spinel phase in these nanoparticles. The FESEM and TEM micrographs revealed the nanoparticles to...
Article
Full-text available
Single-phase pristine and cation-substituted calcium manganite (Ca1−x Bix Mn1−y Vy O3−δ ) polycrystalline samples were synthesized by the solid state reaction technique. Their thermoelectric properties were measured by a set up that was designed and assembled in the laboratory. The Ca1−x Bix Mn1−y Vy O3−δ sample with x = y = 0.04 has shown a power...
Article
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 s...
Article
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 effo...
Article
Full-text available
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. BaFe12O19 as well a...
Article
Curie temperature of polycrystalline barium hexaferrite (BaFe12O19), prepared by conventional solid state technique, is anomalously and significantly enhanced (by nearly 15%) by energetic heavy ion irradiation (150 MeV, Ag12+) at ambient temperature due to dense electronic excitations Moderate fluence (1 × 1012 ions/cm2) induces structural defects...
Article
Electrical conduction behavior of ultrathin (5–110 nm) SnO2 films reactively sputtered at 150–400 °C substrate temperatures is presented. The surface roughness studies revealed that the films with lower thickness were smoother (≤0.6 nm). Stoichiometry/defect structure of the films obtained from X-ray photoelectron spectroscopy data and electron mob...
Article
Full-text available
We present a remarkable enhancement by 300% of the exchange-bias field at room temperature, without affecting the coercivity value, via optimum magnetic annealing (250 °C/3 kOe) in ion-beam sputtered FeMn(30 nm)/NiFe(10 nm) bilayers. This specific behavior has been attributed to a higher degree of γ-FeMn(111) orientation that offers more interfacia...
Article
Full-text available
The significant biaxial anisotropy contribution below 50 K is evidenced and identified as a cause of asymmetric “kinked” magnetization reversal behaviour and strong single cycle training effect in ion-beam sputtered IrMn/NiFe bilayers. The minor loop measurement clearly suggests that the magnetization reversal along the descending branch of the hys...
Article
Full-text available
Magnetoresistance measurements have been employed to demonstrate the thermal evolution of exchange bias, reversal asymmetry and training effect in ion-beam sputtered IrMn/NiFe bilayers. Magnetoresistance investigations have shown a significant increase in exchange bias field and coercivity, pronounced reversal asymmetry and, most prominently, a st...
Article
Full-text available
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...
Data
Full-text available
Magnetoresistance measurements have been employed to demonstrate the thermal evolution of exchange bias, reversal asymmetry and training effect in ion-beam sputtered IrMn/NiFe bilayers. Magnetoresistance investigations have shown a significant increase in exchange bias field and coercivity, pronounced reversal asymmetry and, most prominently, a str...
Article
Full-text available
Photoluminescence (PL) properties of SnO2 films were investigated in a set of polycrystalline SnO2 samples of different thicknesses (10 - 90 nm) deposited by pulsed magnetron reactive sputtering. Structural and electrical properties and defect states of SnO2 films strongly depend upon film thickness. The absence of near-band-edge emission and appea...
Article
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...
Technical Report
Full-text available
Functionally graded tungsten-copper bimetallic compacts with fine microstructure and good mechanical properties have been synthesised by employing microwave heating method at a temperature of 800 °C, in a short time of 30 min. Scanning electron microscopy and energy dispersive X-ray analysis revealed the graded structure of synthesised samples. The...
Article
Full-text available
In this work, we report a study of the influence of large anisotropy of CoFe layer on the reversal asymmetry and training effect in exchange biased IrMn/CoFe bilayers. The existence of a strong single cycle training effect and an accompanying distinct reversal asymmetry at 15 K have been demonstrated using magnetoresistance as a probe. The temperat...
Article
Full-text available
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...
Technical Report
Dense tungsten with fine microstructure has been synthesised by employing plasma assisted microwave sintering method. The observance of fine microstructure in microwave processed tungsten compact is attributed to arrested grain-growth due to rapid heating and cooling characteristics of microwave sintering method. The X-ray diffractograms confirm th...
Article
Full-text available
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 th...
Article
This paper reports the charge transport mechanism at low temperatures in (110) oriented polycrystalline tin oxide (SnO2) films of less than 100 nm thickness prepared by reactive sputtering in the substrate temperature (TS) 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...
Article
Full-text available
Using magnetoresistance as a probe we demonstrate the correlation between reversal asymmetry and training effect in ion-beam sputtered IrMn/NiFe bilayers. During the training procedure, both exchange bias field and the degree of asymmetry decrease monotonically following a very similar trend. The analysis of the magnetoresistance behaviour establis...
Article
Full-text available
Observation of room temperature ferromagnetism (RTFM) is reported in polycrystalline thin films of Ti1−x Mn x O2 (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...
Article
Full-text available
In this paper, we report positive exchange bias (PEB) at room temperature in as-deposited ion-beam sputtered Si(100)/SiO2/CoFe/IrMn/COFeB trilayers without any field cooling protocol. The appearance of positive exchange bias is attributed to the antiferromagnetic coupling between the uncompensated Mn and ferromagnetic (FM) CoFeB spins at the interf...
Article
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 experimen...
Article
Full-text available
The positive exchange bias (PEB) at room temperature in bottom pinned as-deposited IrMn(15 nm)/CoFeB(10 nm) ion-beam sputtered bilayers is reported without any field cooling protocol. The necessary antiferromagnetic coupling of the interfacial spins and uniaxial exchange anisotropy in amorphous ferromagnetic CoFeB are caused by the energetic sputte...
Conference Paper
Full-text available
During past fifteen years, tremendous growth in the field of microwaves, millimeter waves and Terahertz frequency region has been realized in India. The growth of R&D activities in these areas has attracted many multinational companies to start new ventures. The research funding for these activities are mainly provided by government agencies but ma...
Article
Full-text available
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 sec...
Article
Full-text available
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...
Article
In the present paper, DC magnetization investigation on the insulating nanocrystalline powder samples of Ti1-xMnxO2 (x = 0, 0.05, 0.10, and 0.15) prepared by simple chemical route is reported. Structural measurements revealed phase pure anatase structure of TiO2 when x <= 0.05 and a mixture of anatase and rutile TiO2 along with the signature of Mn3...
Conference Paper
Full-text available
Nanowires of Ni 80Fe 20 and Co 90Fe 10 binary alloys were synthesized by direct current electrodeposition in polycarbonate templates. The purpose of this work is to understand the effect of pH and temperature of the bath on the structural and magnetic properties of these galvanostatically electrodeposited nanowires. The increase in both, pH and tem...
Article
Microwaves have been in use for over 80 years in a variety of applications such as communications, characterization of materials, food processing, rubber vulcanization, etc. Microwave heating has revolutionised the synthesis of all kinds of materials including metals, insulators, semiconductors and alloys. The technique can either be employed in a...
Article
Full-text available
In this work dc-magnetization, electronic structural, and Raman investigations of Ti1-xMnxO2 (x = 0.00, 0.05, 0.10, and 0.15) thin films deposited on fused-quartz substrate by a simple and cost effective spray pyrolysis technique have been reported. X-ray diffraction revealed the formation of pure anatase TiO2 phase devoid of elemental Mn clusters...
Article
Full-text available
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...
Conference Paper
The observation of large tunnel magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) employing CoFeB as ferromagnetic electrode(s) and MgO as barrier layer has generated considerable interest for efficient spintronics devices. It is important to understand the correlation of various physical properties of the MTJs with the process parameters...
Conference Paper
Microwave processing, in general, is an energy efficient, rapid and green technique; and in particular, is most energy efficient when it is carried out in a single (electric or magnetic field) mode. Also, it is now established that the technique is capable of processing all kind of materials-ranging from metals to insulators, and in several morphol...
Conference Paper
Hexaferrites are known hard magnetic materials. Soft magnetic materials with low-coercivity and high-remanence are suitable for microwave devices. In this paper, a novel method using microwave energy to transform a hard ferrite in to magnetic soft one is adopted. Microwave processing is capable of modifying the structure/microstructure and giving r...
Article
Full-text available
Long needle-shaped single crystals of Zn1−xCoxO were grown at low temperatures using a molten salt solvent technique, up to x=0.10. The conduction process at low temperatures is determined to be Mott variable range hopping. Both pristine and cobalt-doped crystals clearly exhibit a crossover from negative to positive magnetoresistance as the tempera...
Conference Paper
Ultra thin pristine SnO2 films (50 nm) with (110) orientation were sputter deposited on the glass substrate at 350 to 450C substrate temperatures. It is found that crystallinity and the grain size of the films increases with the increase in the substrate temperature. Films deposited at all substrate temperatures are highly transparent (~90%) and t...
Conference Paper
In the present work, magnetic properties of sputtered IrMn (y nm)/CoFeB (x nm) bilayers were studied systematically as a function of annealing temperature, applied magnetic field and thickness of individual layers. The MOKE loops of the A- and B-series bilayers with x=7, 10, 15 and 20nm and y=5, 10, 15 and 20nm were obtained for both, as-deposited...
Conference Paper
The Fe/MgO/Fe trilayer is an interesting system in which tunnel magnetoresistance (TMR) of ~180% is reported at RT. However, nearly all the work reported on Fe based TMR systems is based on MBE process, which is relatively complex state of art deposition technique (and hence not a commercially viable). In this work, we have attempted to fabricate F...
Conference Paper
Full-text available
The present paper reports on the deposition of high conductivity (10 2ohm-1.cm-1) SnO2 ultrathin films (less than 50 nm) by spray pyrolysis and pulsed dc magnetron reactive sputtering techniques in the presence of electric field. A comparative study has been carried out on the electrical, structural and optical properties of SnO 2 films deposited o...
Conference Paper
Magnetic nanowires are of immense importance in ultrahigh density magnetic storage media, micromagnetic sensors in read heads and spintronics devices. The nanowires of binary alloys of ferromagnetic metals like Co, Ni and Fe are particularly important since they possess high coercivities and high squareness ratio, which is an important requirement...
Conference Paper
Magnetite (Fe3O4) is one of the iron oxides that having distinctive magnetic properties. This oxides crystallizes in cubic inverse spinel form. The band structure calculations of the Fe3O4 suggest a half-metallic structure with a gap in the density of states corresponding to majority carriers. These materials are highly attractive for spintronics a...
Article
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 nanopowders. The addition of copper promotes sintering, and results in grain-growth during sintering, even at a lo...
Article
Full-text available
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 0.38 mu(B)/Co, respectively. The ambient air employed in the present case of the spray pyrolysis pro...
Article
Full-text available
The present paper describes our results on the phase transformation (from crystalline to amorphous) of M-type hard barium hexaferrite, and consequently its conver-sion into soft ferrite by the application of magnetic energy at microwave frequency (2.45 GHz). The rapid volumetric heating of the conventionally prepared polycrystalline hexa-ferrite by...
Article
Microwave processing has revolutionised the synthesis of all kinds of materials including insulators, semiconductors metals and alloys. The technique can either be employed in a mixed mode, separated E-or H-mode or in a combination with other preparation techniques. In no time and at much lower temperatures and power levels, it can even result in n...
Article
Summary form only given. The present paper describes our results on the phase transformation (from crystalline to glassy phase) of both, pristine and substituted W-type hard barium hexaferrites (BaCoxZn2-xFe16O27) into a soft ferrite by the application of magnetic field at microwave frequency (2.45 GHz). Polycrystalline samples of the W-type hexafe...
Article
The Zn[BOND]Ti 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 diel...
Article
A simple theoretical model is developed for studying the magnetic behavior of films at microwave frequencies, and verified experimentally on the ferrite-polymer thick-film samples. The measured values of permeability by the proposed model/technique are found to be in good agreement with the values obtained by the standard cavity perturbation techni...
Article
Journal of Alloys and Compounds j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j a l l c o m Room temperature photoluminescence and dc resistivity of Si 0.95 Ge 0.05 alloy nanowires grown in microwave H-field a b s t r a c t In the present work, Si 0.95 Ge 0.05 alloy nanowires were synthesised in a single-mode reson...
Article
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. Th...
Article
This paper presents a rapid and novel technique of growing nanowires of Si0.75Ge0.25 alloy at 900 °C in less than 10 min by processing the constituents in a TE011 single mode cylindrical resonant cavity, operated at 2.45 GHz and ∼ 300 W. The microstructural, crystal structural, and x-ray photoelectron spectroscopic studies of the nanowires have bee...
Article
Full-text available
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 o...
Article
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 (Zn99.5In0.5)1−xCoxO thin films are deposited by spray p...
Article
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....
Article
Room-temperature ferromagnetism has been observed in Co- or Mn-doped SnO2 and Co- and F-co-doped SnO2 thin films. A maximum magnetic moment of 0.80 mu B/Co ion has been observed for Sn0.90Co0.10O1.925-delta F0.075 thin films, whereas in the case of Sn1-xMnxO2-delta it was 0.18 mu B/Mn ion for x = 0.10. The magnetization of both Sn1-xCoxO2-delta and...
Article
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...
Conference Paper
In the present work, polycrystalline ferromagnetic Zn<sub>0.95</sub>Co<sub>0.05</sub>O samples have been synthesized in a TM<sub>011</sub> single mode cylindrical microwave resonant cavity operating at 2.45 GHz. The synthesized specimen is analyzed for its crystallographic and electronic structure along with magnetic and electron transport properti...
Article
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 produci...
Patent
The present invention discloses a relaxor material lead iron tungstate which has been synthesized in doped and undoped conditions by single and two step heat treatment. The relaxor material is seen to exhibit almost negligible hysteresis and a transducer made thereby shows pressure measurement capability over a wide range from 0.5 MPa to 415 MPa wi...