Mukul Gupta - Academia.edu (original) (raw)

Papers by Mukul Gupta

Defect and Diffusion Forum, 2005

Defect and Diffusion Forum Vols. 242-244 (2005) pp 255-276 © (2005) Trans Tech Publications, Swit... more Defect and Diffusion Forum Vols. 242-244 (2005) pp 255-276 © (2005) Trans Tech Publications, Switzerland doi: 10.4028/www. scientific. net/DDF. 242-244.255 © 2005 Trans Tech Publications, nviitzeriana [16] Probing the Effects of SHI and Doping-lnduced ...

Journal of Non-crystalline Solids, 2004

Thin films of amorphous Fe 85 Zr 15 alloy were deposited by ion-beam sputtering of a composite ta... more Thin films of amorphous Fe 85 Zr 15 alloy were deposited by ion-beam sputtering of a composite target. Analogous to the melt-spun amorphous alloys of similar composition, the crystallization of the amorphous film occurs in two steps, however, with a substantially reduced thermal ...

Physical Review B, 2005

It is demonstrated that x-ray waveguide structures can be used for depth profiling of a marker la... more It is demonstrated that x-ray waveguide structures can be used for depth profiling of a marker layer inside the guiding layer with an accuracy of better than 0.2 nm. A combination of x-ray fluorescence and x-ray reflectivity measurements can provide detailed information about the structure of the guiding layer. The position and thickness of the marker layer affect different aspects of the angle-dependent x-ray fluorescence pattern, thus making it possible to determine the structure of the marker layer in an unambiguous manner. As an example, effects of swift heavy ion irradiation on a Si/ M / Si trilayer ͑M = Fe, W͒, forming the cavity of the waveguide structure, have been studied. It is found that in accordance with the prediction of thermal spike model, Fe is much more sensitive to swift heavy ion induced modifications as compared to W, even in thin film form. However, a clear evidence of movement of the Fe marker layer towards the surface is observed after irradiation, which cannot be understood in terms of the thermal spike model alone.

Physical Review B, 2005

It is demonstrated that nuclear resonance reflectivity from isotopic multilayers can be used as a... more It is demonstrated that nuclear resonance reflectivity from isotopic multilayers can be used as a sensitive technique to study self-diffusion of a Mössbauer isotope ͑ 57 Fe in the present case͒. In the case of isotopic multilayers, in which alternate layers have the same chemical composition and differ only in the abundance of 57 Fe, nuclear resonance scattering causes x-ray scattering contrast between adjacent layers, resulting in the appearance of Bragg peaks corresponding to the bilayer periodicity. Diffusion of 57 Fe across the isotopic interface results in a decrease in the scattering contrast and thus a decrease in the intensity of the Bragg peak, making it possible to measure diffusion lengths of the order of 0.1 nm in chemically homogeneous films. The technique has been used to study self-diffusion of Fe in amorphous FeZr and nanocrystalline FeN alloys. In a-FeZr, measurements yield activation energy for Fe diffusion E = 0.42± 0.05 eV and the pre-exponent factor D 0 = exp͑−39± 1͒ m 2 / s. In nanocrystalline Fe 60 N 40 , variation in diffusivity due to structural relaxation at temperatures as low as 393 K could be observed. Measurements in the structurally relaxed state yield E = 0.8± 0.2 eV and D 0 = exp͑−28± 4͒ m 2 /s.

Physica Status Solidi (c), 2004

In the present work interfacial and microstructural properties of Fe/Ni multilayers having differ... more In the present work interfacial and microstructural properties of Fe/Ni multilayers having different thickness of constituent layers, were studied using grazing incidence X-ray diffraction and reflectivity techniques. The chemical nature of the interfaces involved was investigated using X-ray photoelectron spectroscopy depth profiling. It has been found that microstructural properties show a variation with a changed bilayers structure. The correlation between the microstructural and magnetic properties reveals that a different nature of magnetostriction and crystal structure is mainly responsible for the observed magnetization behavior in Fe/Ni multilayers having different thickness ratio of Fe and Ni. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Physical Review B, 2005

Thin films of iron and permalloy Ni80Fe20 were prepared using an Ar+N2 mixture with magnetron spu... more Thin films of iron and permalloy Ni80Fe20 were prepared using an Ar+N2 mixture with magnetron sputtering technique at ambient temperature. The nitrogen partial pressure, during sputtering process was varied in the range of 0 to 100%, keeping the total gas flow at constant. At lower nitrogen pressures RN2<33% both Fe and NiFe, first form a nanocrystalline structure and an increase in nitrogen partail pressure results in formation of an amorphous structure. At intermediate nitrogen partial pressures, nitrides of Fe and NiFe were obtained while at even higher nitrogen partial pressures, nitrides themselves became nanocrystalline or amorphous. The surface, structural and magnetic properties of the deposited films were studied using x-ray reflection and diffraction, transmission electron microscopy, polarized neutron reflectivity and using a DC extraction magnetometer. The growth behavior for amorphous film was found different as compared with poly or nanocrystalline films. The soft-magnetic properties of FeN were improved on nanocrystallization while those of NiFeN were degraded. A mechanism inducing nanocrystallization and amorphization in Fe and NiFe due to reactive nitrogen sputtering is discussed in the present article.

Physical Review B, 2004

Self-diffusion of iron in natural Fe 67 Zr 33 / 57 Fe 67 Zr 33 multilayers has been investigated ... more Self-diffusion of iron in natural Fe 67 Zr 33 / 57 Fe 67 Zr 33 multilayers has been investigated by neutron reflectometry. The as-deposited multilayer is amorphous in nature. It remains amorphous up to a temperature of 573 K and thereafter nanocrystallizes with an average grain size of 6 nm. The self-diffusion in the multilayers has been measured after isothermal vacuum annealing below the nanocrystallization temperature by monitoring the decay of the intensity of the first order Bragg peak, arising due to the isotopic periodicity. It has been found that the diffusivity at different temperatures follows an Arrhenius-type behavior with the preexponential factor D 0 =5ϫ 10 −18±1 m 2 s −1 and the activation energy E = 0.38± 0.05 eV, respectively. These values of E and D 0 follow the well-known E -D 0 correlation and on the basis of this correlation it is suggested that diffusion mechanism in the present case is not highly collective but involves a rather small group of atoms.

Journal of The Physical Society of Japan, 2004

Amorphous alloy of Fe-N with ˜40 at.% N has been prepared by reactive ion-beam sputtering. A syst... more Amorphous alloy of Fe-N with ˜40 at.% N has been prepared by reactive ion-beam sputtering. A systematic study of the growth behaviour, thermal stability, atomic diffusion and the magnetic properties of the alloy has been done. Deposition characteristics of the film have been studied using the x-ray reflectivity and the atomic force microscopy techniques. The results suggest that it is a suitable system for preparing isotopic multilayers for application as the nuclear Bragg monochromator. Pure nuclear Bragg reflections have been observed from an isotopic multilayer of composition: float glass (substrate)/[natFeN0.7(30 Å)/57FeN0.7(20 Å)]× 10/natFeN0.7(30 Å). A nuclear Bragg peak because of isotopic periodicity is observed at an angle of 0.55°. where the electronic scattering is of the order of 10-3. A nuclear reflectivity of 2.5% has been obtained at the first Bragg peak.

Acta Materialia, 2009

Simultaneous self-diffusion measurements of Fe and N in amorphous Fe 86 N 14 alloy using secondar... more Simultaneous self-diffusion measurements of Fe and N in amorphous Fe 86 N 14 alloy using secondary ion mass spectroscopy (SIMS) are reported. In addition, neutron reflectivity (NR) was used to study the Fe self-diffusion in the same compound. The broadening of a tracer layer of 57 Fe 15 86 N 14 sandwiched between Fe 86 N 14 layers was observed by SIMS measurements after the annealing of films at different temperatures. A decay of the Bragg peak intensity after isothermal annealing was also observed in ½Fe 86 N 14 = 57 Fe 86 N 14 10 multilayers in NR. It was observed by SIMS measurements that Fe diffusion was about 2 orders of magnitude smaller than N, even though the structural relaxation times for Fe and N were almost identical. This is an important result, indicating that the relaxation time of diffusion is basically driven by the relaxation of the structure itself.

Applied Surface Science, 2003

An ion-beam sputtering (IBS) system has been designed and developed for preparing thin ®lms and m... more An ion-beam sputtering (IBS) system has been designed and developed for preparing thin ®lms and multilayers of various elements, alloys and compounds. The ion source used is a 3 cm diameter, hot-cathode Kaufman type 1.5 kV ion source. The system has been successfully tested with the deposition of various materials, and the deposition parameters were optimised for achieving good quality of thin ®lms and multilayers. A systematic illustration of the versatility of the system to produce a variety of structures is done by depositing thin ®lm of pure iron, an alloy ®lm of Fe±Zr, a compound thin ®lm of FeN, a multilayer of Fe± Ag and an isotopic multilayer of 57 FeZr/FeZr. Microstructural measurements on these ®lms using X-ray and neutron re¯ectivity, atomic force microscopy (AFM), and X-ray diffraction are presented and discussed to reveal the quality of the microstructures obtained with the system. It is found that in general, the surface roughnesses of the ®lm deposited by IBS are signi®cantly smaller as compared to those for ®lms deposited by e-beam evaporation. Further, the grain size of the IBS crystalline ®lms is signi®cantly re®ned as compared to the ®lms deposited by e-beam evaporation. Grain re®nement may be one of the reasons for reduced surface roughness. In the case of amorphous ®lms, the roughness of the ®lms does not increase appreciably beyond that of the substrate even after depositing thicknesses of several hundred angstroms. #

Applied Surface Science, 2004

This paper deals with the investigation of interfacial properties and their influence on magnetiz... more This paper deals with the investigation of interfacial properties and their influence on magnetization behaviour of Fe/Ni multilayer (ML) structures. Two types of multilayer structures with nominal composition of [Fe(29 Å)/Ni(86 Å)] 10 and [Fe(50 Å)/Ni(50 Å)] 10 were prepared with ...

Journal of Alloys and Compounds, 2001

Thin films of iron nitrides were deposited by pulsed laser deposition at different nitrogen press... more Thin films of iron nitrides were deposited by pulsed laser deposition at different nitrogen pressures. Depositions were done both in the presence as well as absence of glow-discharge around the substrate. Films deposited without glow-discharge were essentially ferromagnetic in nature and exhibited a structural evolution from b.c.c.→b.c.t.→f.c.c.→h.c.p.→orthorhombic phases as the nitrogen pressure during the deposition increased. As a result of glow-discharge during the deposition process, increased nitridation is obtained and formation of new-cubic-type Fe-N phases occur.

Acta Materialia, 2008

Self-diffusion of the atomic constituents in the solid state is a fundamental transport process t... more Self-diffusion of the atomic constituents in the solid state is a fundamental transport process that controls various materials properties. With established methods of diffusivity determination it is only possible to measure diffusion processes on a length scale down to 10 nm at corresponding diffusivities of 10 À23 m 2 s À1 . However, for complex materials like amorphous or nano-structured solids the given values are often not sufficient for a proper characterization. Consequently, it is necessary to detect diffusion length well below 1 nm. Here, we present the method of neutron reflectometry on isotope multilayers. For two model systems, an amorphous semiconductor and an amorphous metallic alloy, the efficiency of this method is demonstrated to detect minimum diffusion lengths of only 0.6-0.7 nm. It is further shown that diffusivities can be derived which are more than two orders of magnitude lower than those obtainable with conventional methods. Prospects of this method in order to solve actual kinetic problems in materials science are given.

Defect and Diffusion Forum, 2005

a mukul.gupta@psi.ch, b agupta@udc.ernet.in, c thomas.gutberlet@psi.ch

Physical Review B, 2002

The measurement of self-diffusion of iron in amorphous FeN 0.7 using secondary-ion mass spectrosc... more The measurement of self-diffusion of iron in amorphous FeN 0.7 using secondary-ion mass spectroscopy is reported. Diffusion broadening of tracer layers of 57 FeN 0.7 was observed after isothermal vacuum annealing of the films at different temperatures. Strong structural relaxation ...

Electrochemical and Solid State Letters, 2006

The structural and magnetic properties of Ni-Cu thin film on a Si͑111͒ substrate, grown by the el... more The structural and magnetic properties of Ni-Cu thin film on a Si͑111͒ substrate, grown by the electrodeposition method, have been studied using room-temperature neutron reflectometry, X-ray diffraction ͑XRD͒, and atomic force microscopy ͑AFM͒ techniques. The structural parameters of the thin film have been extracted from unpolarized neutron reflectometry measurements. The polarized neutron reflectivity measurement showed that there is a reduction in the magnetic moment of a Ni atom compared to its bulk value in the layer as well as at the interfaces. XRD shows crystalline growth of the film. The correlation factors quantifying the morphology of the Ni-air interface have been obtained from AFM measurements.

Vacuum, 2001

An amorphous iron nitride thin film was deposited using reactive ion beam sputtering of iron by a... more An amorphous iron nitride thin film was deposited using reactive ion beam sputtering of iron by a beam of argon and nitrogen ions. Nitrogen content in the film as determined from conversion electron Mössbauer spectroscopy (CEMS) and X-ray photoelectron spectroscopy (XPS) ...

Hyperfine Interactions, 2008

It is shown that x-ray reflectivity and x-ray fluorescence under standing wave conditions can be ... more It is shown that x-ray reflectivity and x-ray fluorescence under standing wave conditions can be used to study atomic diffusion with an accuracy of a fraction of a nanometer. Both the techniques can be made isotope selective by making use of nuclear resonance scattering from a Mössbauer active isotope. The techniques have been used to study self-diffusion of Fe in amorphous and nano-crystalline alloys of FeZr and FeN. The observed correlation of the activation energy E with pre-exponent factor D0 confirms that in amorphous FeZr alloy diffusion takes place via collective motion of a group of atoms. Even in nanocrystalline alloys it is found that atomic diffusion occurs mainly through grain boundaries which are amorphous or highly disordered in nature.

Materials Science Forum, 2005

Materials Science Forum Vols. 480-481 (2005) pp 557-564 Online available since 2005/Mar/15 at www... more Materials Science Forum Vols. 480-481 (2005) pp 557-564 Online available since 2005/Mar/15 at www.scientific.net © (2005) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/MSF.480-481.557 ... All rights reserved. No part of ...

Journal of Molecular Biology, 2005

The electrical and magnetic transport properties of the La 0.67Kx Eu x Ca 0.33 MnO 3 system exhib... more The electrical and magnetic transport properties of the La 0.67Kx Eu x Ca 0.33 MnO 3 system exhibit lowering of insulator to metal and paramagnetic to ferromagnetic transition temperature (T C ) with the increase of Eu concentration in addition to possessing CMR property. The temperature variation of electrical resistivity and magnetic susceptibility for xZ0.21 is found to have two distinct regions in the paramagnetic state for TOT P ; one with the localization of lattice polaron in the high-temperature region (TO1.5T P ) satisfying the dynamics of variable range hopping (VRH) model and the other being the combination of the spin and lattice polarons in the region T P !T!1.5T P . The resistivity variation with temperature and magnetic field, the cusp in the resistivity peak and CMR phenomenon are interpreted in terms of coexistence of spin and lattice small polarons in the intermediate region (T P !T!1.5T P ). The spin polaron energy in the La 0.46 Eu 0.21 Ca 0.33 MnO 3 system is estimated to be 106.73G0.90 meV and this energy decreases with the increase of external magnetic field. The MR ratio is maximal with a value of 99.99% around the transition temperature and this maximum persists till T/0 K, at the field of 8 T. q

Defect and Diffusion Forum, 2005

Defect and Diffusion Forum Vols. 242-244 (2005) pp 255-276 © (2005) Trans Tech Publications, Swit... more Defect and Diffusion Forum Vols. 242-244 (2005) pp 255-276 © (2005) Trans Tech Publications, Switzerland doi: 10.4028/www. scientific. net/DDF. 242-244.255 © 2005 Trans Tech Publications, nviitzeriana [16] Probing the Effects of SHI and Doping-lnduced ...

Journal of Non-crystalline Solids, 2004

Thin films of amorphous Fe 85 Zr 15 alloy were deposited by ion-beam sputtering of a composite ta... more Thin films of amorphous Fe 85 Zr 15 alloy were deposited by ion-beam sputtering of a composite target. Analogous to the melt-spun amorphous alloys of similar composition, the crystallization of the amorphous film occurs in two steps, however, with a substantially reduced thermal ...

Physical Review B, 2005

It is demonstrated that x-ray waveguide structures can be used for depth profiling of a marker la... more It is demonstrated that x-ray waveguide structures can be used for depth profiling of a marker layer inside the guiding layer with an accuracy of better than 0.2 nm. A combination of x-ray fluorescence and x-ray reflectivity measurements can provide detailed information about the structure of the guiding layer. The position and thickness of the marker layer affect different aspects of the angle-dependent x-ray fluorescence pattern, thus making it possible to determine the structure of the marker layer in an unambiguous manner. As an example, effects of swift heavy ion irradiation on a Si/ M / Si trilayer ͑M = Fe, W͒, forming the cavity of the waveguide structure, have been studied. It is found that in accordance with the prediction of thermal spike model, Fe is much more sensitive to swift heavy ion induced modifications as compared to W, even in thin film form. However, a clear evidence of movement of the Fe marker layer towards the surface is observed after irradiation, which cannot be understood in terms of the thermal spike model alone.

Physical Review B, 2005

It is demonstrated that nuclear resonance reflectivity from isotopic multilayers can be used as a... more It is demonstrated that nuclear resonance reflectivity from isotopic multilayers can be used as a sensitive technique to study self-diffusion of a Mössbauer isotope ͑ 57 Fe in the present case͒. In the case of isotopic multilayers, in which alternate layers have the same chemical composition and differ only in the abundance of 57 Fe, nuclear resonance scattering causes x-ray scattering contrast between adjacent layers, resulting in the appearance of Bragg peaks corresponding to the bilayer periodicity. Diffusion of 57 Fe across the isotopic interface results in a decrease in the scattering contrast and thus a decrease in the intensity of the Bragg peak, making it possible to measure diffusion lengths of the order of 0.1 nm in chemically homogeneous films. The technique has been used to study self-diffusion of Fe in amorphous FeZr and nanocrystalline FeN alloys. In a-FeZr, measurements yield activation energy for Fe diffusion E = 0.42± 0.05 eV and the pre-exponent factor D 0 = exp͑−39± 1͒ m 2 / s. In nanocrystalline Fe 60 N 40 , variation in diffusivity due to structural relaxation at temperatures as low as 393 K could be observed. Measurements in the structurally relaxed state yield E = 0.8± 0.2 eV and D 0 = exp͑−28± 4͒ m 2 /s.

Physica Status Solidi (c), 2004

In the present work interfacial and microstructural properties of Fe/Ni multilayers having differ... more In the present work interfacial and microstructural properties of Fe/Ni multilayers having different thickness of constituent layers, were studied using grazing incidence X-ray diffraction and reflectivity techniques. The chemical nature of the interfaces involved was investigated using X-ray photoelectron spectroscopy depth profiling. It has been found that microstructural properties show a variation with a changed bilayers structure. The correlation between the microstructural and magnetic properties reveals that a different nature of magnetostriction and crystal structure is mainly responsible for the observed magnetization behavior in Fe/Ni multilayers having different thickness ratio of Fe and Ni. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Physical Review B, 2005

Thin films of iron and permalloy Ni80Fe20 were prepared using an Ar+N2 mixture with magnetron spu... more Thin films of iron and permalloy Ni80Fe20 were prepared using an Ar+N2 mixture with magnetron sputtering technique at ambient temperature. The nitrogen partial pressure, during sputtering process was varied in the range of 0 to 100%, keeping the total gas flow at constant. At lower nitrogen pressures RN2<33% both Fe and NiFe, first form a nanocrystalline structure and an increase in nitrogen partail pressure results in formation of an amorphous structure. At intermediate nitrogen partial pressures, nitrides of Fe and NiFe were obtained while at even higher nitrogen partial pressures, nitrides themselves became nanocrystalline or amorphous. The surface, structural and magnetic properties of the deposited films were studied using x-ray reflection and diffraction, transmission electron microscopy, polarized neutron reflectivity and using a DC extraction magnetometer. The growth behavior for amorphous film was found different as compared with poly or nanocrystalline films. The soft-magnetic properties of FeN were improved on nanocrystallization while those of NiFeN were degraded. A mechanism inducing nanocrystallization and amorphization in Fe and NiFe due to reactive nitrogen sputtering is discussed in the present article.

Physical Review B, 2004

Self-diffusion of iron in natural Fe 67 Zr 33 / 57 Fe 67 Zr 33 multilayers has been investigated ... more Self-diffusion of iron in natural Fe 67 Zr 33 / 57 Fe 67 Zr 33 multilayers has been investigated by neutron reflectometry. The as-deposited multilayer is amorphous in nature. It remains amorphous up to a temperature of 573 K and thereafter nanocrystallizes with an average grain size of 6 nm. The self-diffusion in the multilayers has been measured after isothermal vacuum annealing below the nanocrystallization temperature by monitoring the decay of the intensity of the first order Bragg peak, arising due to the isotopic periodicity. It has been found that the diffusivity at different temperatures follows an Arrhenius-type behavior with the preexponential factor D 0 =5ϫ 10 −18±1 m 2 s −1 and the activation energy E = 0.38± 0.05 eV, respectively. These values of E and D 0 follow the well-known E -D 0 correlation and on the basis of this correlation it is suggested that diffusion mechanism in the present case is not highly collective but involves a rather small group of atoms.

Journal of The Physical Society of Japan, 2004

Amorphous alloy of Fe-N with ˜40 at.% N has been prepared by reactive ion-beam sputtering. A syst... more Amorphous alloy of Fe-N with ˜40 at.% N has been prepared by reactive ion-beam sputtering. A systematic study of the growth behaviour, thermal stability, atomic diffusion and the magnetic properties of the alloy has been done. Deposition characteristics of the film have been studied using the x-ray reflectivity and the atomic force microscopy techniques. The results suggest that it is a suitable system for preparing isotopic multilayers for application as the nuclear Bragg monochromator. Pure nuclear Bragg reflections have been observed from an isotopic multilayer of composition: float glass (substrate)/[natFeN0.7(30 Å)/57FeN0.7(20 Å)]× 10/natFeN0.7(30 Å). A nuclear Bragg peak because of isotopic periodicity is observed at an angle of 0.55°. where the electronic scattering is of the order of 10-3. A nuclear reflectivity of 2.5% has been obtained at the first Bragg peak.

Acta Materialia, 2009

Simultaneous self-diffusion measurements of Fe and N in amorphous Fe 86 N 14 alloy using secondar... more Simultaneous self-diffusion measurements of Fe and N in amorphous Fe 86 N 14 alloy using secondary ion mass spectroscopy (SIMS) are reported. In addition, neutron reflectivity (NR) was used to study the Fe self-diffusion in the same compound. The broadening of a tracer layer of 57 Fe 15 86 N 14 sandwiched between Fe 86 N 14 layers was observed by SIMS measurements after the annealing of films at different temperatures. A decay of the Bragg peak intensity after isothermal annealing was also observed in ½Fe 86 N 14 = 57 Fe 86 N 14 10 multilayers in NR. It was observed by SIMS measurements that Fe diffusion was about 2 orders of magnitude smaller than N, even though the structural relaxation times for Fe and N were almost identical. This is an important result, indicating that the relaxation time of diffusion is basically driven by the relaxation of the structure itself.

Applied Surface Science, 2003

An ion-beam sputtering (IBS) system has been designed and developed for preparing thin ®lms and m... more An ion-beam sputtering (IBS) system has been designed and developed for preparing thin ®lms and multilayers of various elements, alloys and compounds. The ion source used is a 3 cm diameter, hot-cathode Kaufman type 1.5 kV ion source. The system has been successfully tested with the deposition of various materials, and the deposition parameters were optimised for achieving good quality of thin ®lms and multilayers. A systematic illustration of the versatility of the system to produce a variety of structures is done by depositing thin ®lm of pure iron, an alloy ®lm of Fe±Zr, a compound thin ®lm of FeN, a multilayer of Fe± Ag and an isotopic multilayer of 57 FeZr/FeZr. Microstructural measurements on these ®lms using X-ray and neutron re¯ectivity, atomic force microscopy (AFM), and X-ray diffraction are presented and discussed to reveal the quality of the microstructures obtained with the system. It is found that in general, the surface roughnesses of the ®lm deposited by IBS are signi®cantly smaller as compared to those for ®lms deposited by e-beam evaporation. Further, the grain size of the IBS crystalline ®lms is signi®cantly re®ned as compared to the ®lms deposited by e-beam evaporation. Grain re®nement may be one of the reasons for reduced surface roughness. In the case of amorphous ®lms, the roughness of the ®lms does not increase appreciably beyond that of the substrate even after depositing thicknesses of several hundred angstroms. #

Applied Surface Science, 2004

This paper deals with the investigation of interfacial properties and their influence on magnetiz... more This paper deals with the investigation of interfacial properties and their influence on magnetization behaviour of Fe/Ni multilayer (ML) structures. Two types of multilayer structures with nominal composition of [Fe(29 Å)/Ni(86 Å)] 10 and [Fe(50 Å)/Ni(50 Å)] 10 were prepared with ...

Journal of Alloys and Compounds, 2001

Thin films of iron nitrides were deposited by pulsed laser deposition at different nitrogen press... more Thin films of iron nitrides were deposited by pulsed laser deposition at different nitrogen pressures. Depositions were done both in the presence as well as absence of glow-discharge around the substrate. Films deposited without glow-discharge were essentially ferromagnetic in nature and exhibited a structural evolution from b.c.c.→b.c.t.→f.c.c.→h.c.p.→orthorhombic phases as the nitrogen pressure during the deposition increased. As a result of glow-discharge during the deposition process, increased nitridation is obtained and formation of new-cubic-type Fe-N phases occur.

Acta Materialia, 2008

Self-diffusion of the atomic constituents in the solid state is a fundamental transport process t... more Self-diffusion of the atomic constituents in the solid state is a fundamental transport process that controls various materials properties. With established methods of diffusivity determination it is only possible to measure diffusion processes on a length scale down to 10 nm at corresponding diffusivities of 10 À23 m 2 s À1 . However, for complex materials like amorphous or nano-structured solids the given values are often not sufficient for a proper characterization. Consequently, it is necessary to detect diffusion length well below 1 nm. Here, we present the method of neutron reflectometry on isotope multilayers. For two model systems, an amorphous semiconductor and an amorphous metallic alloy, the efficiency of this method is demonstrated to detect minimum diffusion lengths of only 0.6-0.7 nm. It is further shown that diffusivities can be derived which are more than two orders of magnitude lower than those obtainable with conventional methods. Prospects of this method in order to solve actual kinetic problems in materials science are given.

Defect and Diffusion Forum, 2005

a mukul.gupta@psi.ch, b agupta@udc.ernet.in, c thomas.gutberlet@psi.ch

Physical Review B, 2002

The measurement of self-diffusion of iron in amorphous FeN 0.7 using secondary-ion mass spectrosc... more The measurement of self-diffusion of iron in amorphous FeN 0.7 using secondary-ion mass spectroscopy is reported. Diffusion broadening of tracer layers of 57 FeN 0.7 was observed after isothermal vacuum annealing of the films at different temperatures. Strong structural relaxation ...

Electrochemical and Solid State Letters, 2006

The structural and magnetic properties of Ni-Cu thin film on a Si͑111͒ substrate, grown by the el... more The structural and magnetic properties of Ni-Cu thin film on a Si͑111͒ substrate, grown by the electrodeposition method, have been studied using room-temperature neutron reflectometry, X-ray diffraction ͑XRD͒, and atomic force microscopy ͑AFM͒ techniques. The structural parameters of the thin film have been extracted from unpolarized neutron reflectometry measurements. The polarized neutron reflectivity measurement showed that there is a reduction in the magnetic moment of a Ni atom compared to its bulk value in the layer as well as at the interfaces. XRD shows crystalline growth of the film. The correlation factors quantifying the morphology of the Ni-air interface have been obtained from AFM measurements.

Vacuum, 2001

An amorphous iron nitride thin film was deposited using reactive ion beam sputtering of iron by a... more An amorphous iron nitride thin film was deposited using reactive ion beam sputtering of iron by a beam of argon and nitrogen ions. Nitrogen content in the film as determined from conversion electron Mössbauer spectroscopy (CEMS) and X-ray photoelectron spectroscopy (XPS) ...

Hyperfine Interactions, 2008

It is shown that x-ray reflectivity and x-ray fluorescence under standing wave conditions can be ... more It is shown that x-ray reflectivity and x-ray fluorescence under standing wave conditions can be used to study atomic diffusion with an accuracy of a fraction of a nanometer. Both the techniques can be made isotope selective by making use of nuclear resonance scattering from a Mössbauer active isotope. The techniques have been used to study self-diffusion of Fe in amorphous and nano-crystalline alloys of FeZr and FeN. The observed correlation of the activation energy E with pre-exponent factor D0 confirms that in amorphous FeZr alloy diffusion takes place via collective motion of a group of atoms. Even in nanocrystalline alloys it is found that atomic diffusion occurs mainly through grain boundaries which are amorphous or highly disordered in nature.

Materials Science Forum, 2005

Materials Science Forum Vols. 480-481 (2005) pp 557-564 Online available since 2005/Mar/15 at www... more Materials Science Forum Vols. 480-481 (2005) pp 557-564 Online available since 2005/Mar/15 at www.scientific.net © (2005) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/MSF.480-481.557 ... All rights reserved. No part of ...

Journal of Molecular Biology, 2005

The electrical and magnetic transport properties of the La 0.67Kx Eu x Ca 0.33 MnO 3 system exhib... more The electrical and magnetic transport properties of the La 0.67Kx Eu x Ca 0.33 MnO 3 system exhibit lowering of insulator to metal and paramagnetic to ferromagnetic transition temperature (T C ) with the increase of Eu concentration in addition to possessing CMR property. The temperature variation of electrical resistivity and magnetic susceptibility for xZ0.21 is found to have two distinct regions in the paramagnetic state for TOT P ; one with the localization of lattice polaron in the high-temperature region (TO1.5T P ) satisfying the dynamics of variable range hopping (VRH) model and the other being the combination of the spin and lattice polarons in the region T P !T!1.5T P . The resistivity variation with temperature and magnetic field, the cusp in the resistivity peak and CMR phenomenon are interpreted in terms of coexistence of spin and lattice small polarons in the intermediate region (T P !T!1.5T P ). The spin polaron energy in the La 0.46 Eu 0.21 Ca 0.33 MnO 3 system is estimated to be 106.73G0.90 meV and this energy decreases with the increase of external magnetic field. The MR ratio is maximal with a value of 99.99% around the transition temperature and this maximum persists till T/0 K, at the field of 8 T. q