Metals and their alloys are highly susceptible to corrosion in wet environment. Dealloying is a p... more Metals and their alloys are highly susceptible to corrosion in wet environment. Dealloying is a particular type of corrosion, attacking practically all metals in industrial use: When an alloy is coming into contact with an electrolyte, the less noble metal may go into solution, typically causing crack formation and subsequent material failure upon stress. We used bulk sensitive Hard X-ray
Nanosized particles of Ni 0.25 Co 0.25 Zn 0.5 Fe 2 O 4 have been synthesized by chemical coprecip... more Nanosized particles of Ni 0.25 Co 0.25 Zn 0.5 Fe 2 O 4 have been synthesized by chemical coprecipitation method. Exchange-bias phenomenon arising from the core-shell interaction has been investigated using a combination of in-field, low-temperature Mössbauer spectroscopy and dc magnetization. To understand the clear mechanism of interaction and exchange bias, isothermal remanence magnetization-dc demagnetization and M-H loops at different cooling field have been taken. The observed variation in coercivity H C and exchange-bias field H E confirms that only core is affected by the cooling field. The slope of the Henkel plot is 1.82, indicating the noninteracting nature of the particles. In-field Mössbauer spectroscopy clearly establishes the core and shell contributions and also confirms that 70% of spins are in the shell. The barrier energy has been estimated to be 17ϫ 10 −14 ergs which accounts for the fact that the shell is not affected by application of as large a field as 5 T.
Nanocomposites with magnetic components possessing nanometric dimensions, lying in the range 1-10... more Nanocomposites with magnetic components possessing nanometric dimensions, lying in the range 1-10 nm, are found to be exhibiting superior physical properties with respect to their coarser sized counterparts. Magnetic nanocomposites based on gamma iron oxide embedded in a polymer matrix have been prepared and characterized. The behaviour of these samples at low temperatures have been studied using Mössbauer spectroscopy. Mössbauer studies indicate that the composites consist of very fine particles of γ γ-Fe 2 O 3 of which some amount exists in the superparamagnetic phase. The cycling of the preparative conditions were found to increase the amount of γ γ-Fe 2 O 3 in the matrix.
Reactive ion-beam sputtering has been used to prepare iron nitride over a wide composition range.... more Reactive ion-beam sputtering has been used to prepare iron nitride over a wide composition range. It is found that the samples deposited at room temperature exhibit amorphous phase in the composition range from 12 at. % nitrogen to 23 at. % nitrogen. For samples deposited at liquid nitrogen temperature the system is amorphous up to 35 at. % nitrogen. Amorphization can be understood in terms of a frustration in the system due to a competition between ␣ and phases. Kinetic constraints are also found to play a role in the amorphization process. Mössbauer measurements suggest that the local order in the amorphous phase consists of a mixture of ␣-Fe-like and-Fe 3 N-like short-range orders. On the iron rich side the amorphous phase exhibits two-step crystallization, with a primary ␣-Fe phase precipitating out in the first step. Around 22 at. % nitrogen the system exhibits a single step isomorphous transformation to phase. Thus, amorphous iron nitride phases exhibit behavior very similar to the conventional transition metal-metalloid amorphous alloys. In the remaining composition range nanocrystalline phases are formed. The amorphous magnetic iron nitride phases are expected to have distinct advantages over their crystalline counterparts in terms of soft magnetic applications.
The mechanism of stress relaxation in nanocrystalline Fe-N thin film has been studied. The as-dep... more The mechanism of stress relaxation in nanocrystalline Fe-N thin film has been studied. The as-deposited film possesses a strong in-plane compressive stress which relaxes with thermal annealing. Precise diffusion measurements using nuclear resonance reflectivity show that stress relaxation does not involve any long-range diffusion of Fe atoms. Rather, a redistribution of nitrogen atoms at various interstitial sites, as evidenced by conversion electron Mössbauer spectroscopy, is responsible for the relaxation of internal stresses. On the other hand, formation of the γ-Fe 4 N phase at temperatures above 523 K involves long-range rearrangement of Fe atoms. The activation energy for Fe self-diffusion is found to be 0.38 ± 0.04 eV.
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.
The occurrence of bulk superconductivity at ~22 K is reported in polycrystalline samples of BaFe ... more The occurrence of bulk superconductivity at ~22 K is reported in polycrystalline samples of BaFe 2-x Ru x As 2 for nominal Ru content in the range of x=0.75 to 1.125. A systematic suppression of the spin density wave transition temperature (T SDW) precedes the appearance of superconductivity in the system. A phase diagram is proposed based on the measured T SDW and superconducting transition temperature (T C) variations as a function of Ru composition. Band structure calculations, indicate introduction of electron carriers in the system upon Ru substitutiom. The calculated magnetic moment on Fe shows a minimum at x=1.0, suggesting that the suppression of the magnetic moment is associated with the emergence of superconductivity. Results of low temperature and high field Mossbauer measurements are presented. These indicate weakening of magnetic interaction with Ru substitution
The effect of Cr substitution into nanocrystalline Co-Zn ferrite prepared by the chemical copreci... more The effect of Cr substitution into nanocrystalline Co-Zn ferrite prepared by the chemical coprecipitation method has been studied. Mössbauer studies at a temperature ͑20 K͒ well below the blocking temperatures of the samples show that Cr goes preferentially into the octahedral B site and that the hyperfine fields at both A and B sites decrease with increase in Cr concentration. Based on the cation distribution obtained from fitting Mössbauer spectra, structural parameters such as lattice parameters, site bond and edge lengths, and the oxygen parameter u have been calculated. The trend of theoretically calculated lattice parameter with Cr content matches well with the experimentally obtained values.
Preliminary results on magnetic and transport properties of a thin film of disordered Fe 2 CrAl d... more Preliminary results on magnetic and transport properties of a thin film of disordered Fe 2 CrAl deposited on (111) Si by pulsed laser deposition is reported in this study. While the bulk arc melted ingot used as target for the deposition is purely ferromagnetic, the film shows the coexistence of different magnetic phases, which arises due to the granular nature of the film. This is because, although the average composition pertains to Fe 2 CrAl, local disorder results in the formation of grains with different magnetic states that may be ferromagnetic or may consist of magnetic clusters. The resulting magnetic inhomogeneity of the thin film leads to large values of negative temperature coefficient of resistance of $22%/K at 260 K.
We have studied the origin of a counter intuitive diffusion behavior of Fe and N atoms in a iron ... more We have studied the origin of a counter intuitive diffusion behavior of Fe and N atoms in a iron mononitride (FeN) thin film. It was observed that in-spite of a larger atomic size, Fe tend to diffuse more rapidly than smaller N atoms. This only happens in the N-rich region of Fe-N phase diagram, in the N-poor regions, N diffusion coefficient is orders of magnitude larger than Fe. Detailed selfdiffusion measurements performed in FeN thin films reveal that the diffusion mechanism of Fe and N is different-Fe atoms diffuse through a complex process, which in addition to a volume diffusion, predominantly controlled by a fast grain boundary diffusion. On the other hand N atoms diffuse through a classical volume-type diffusion process. Observed results have been explained in terms of stronger Fe-N (than Fe-Fe) bonds generally predicted theoretically for mononitride compositions of transition metals.
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.
Electronically mediated sputtering in thin gold films, bombarded with 200-MeV Ag ions, has been o... more Electronically mediated sputtering in thin gold films, bombarded with 200-MeV Ag ions, has been observed by ex-situ thickness measurements of the film using x-ray reflectivity technique. The observed sputter yield depends upon the film thickness and is about 410 atoms per incident ion for films of thickness 150 Å and 235 atoms per incident ion in 450-Å-thick film. This sputtering rate is a few orders of magnitude higher as compared to that normally encountered in the regime of elastic collisions. Reduced mobility of the electrons due to scattering from the surface and the grain boundaries plays an important role in enhancing the effects of electronic excitations. Sputtering is accompanied by a significant smoothening of the film surface and smearing of the boundaries between the grains.
In this work, we studied phase formation, structural and magnetic properties of iron-nitride (Fe-... more In this work, we studied phase formation, structural and magnetic properties of iron-nitride (Fe-N) thin films deposited using high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (dc-MS). The nitrogen partial pressure during deposition was systematically varied both in HiPIMS and dc-MS. Resulting Fe-N films were characterized for their microstructure, magnetic properties and nitrogen concentration. We found that HiPIMS deposited Fe-N films show a globular nanocrystalline microstructure and improved soft magnetic properties. In addition, it was found that the nitrogen reactivity impedes in HiPIMS as compared to dc-MS. Obtained results can be understood in terms of distinct plasma properties of HiPIMS.
In this work we studied Cu/Co multilayers prepared using dc-magnetron sputtering technique with A... more In this work we studied Cu/Co multilayers prepared using dc-magnetron sputtering technique with Ag surfactant. It was found that Ag balances the difference in the surface free energy of Cu and Co and this results in removing the asymmetry in the interface roughness of Cu-on-Co and Co-on-Cu interfaces. As the interfaces become symmetric, we observe a significant enhancement in antiferromagnetic coupling and magneto resistance. Further, a correlation of spin-dependent scattering with the interface roughness is brought by comparing Cu/Co multilayer prepared using different deposition methods. It was found that as interface roughness increases spin-dependent scattering decreases.
Resonance enhancement of x rays in a thin film and fluorescence emission from embedded marker lay... more Resonance enhancement of x rays in a thin film and fluorescence emission from embedded marker layers within the film have been studied. With embedded marker layers of Ti, Fe, and W at different depths in a thin Si film on a Au-coated Si substrate, it has been shown that the position of a marker layer throughout the depth of the film can be unambiguously determined with a precision better than 0.5 nm. In this example, fieldintensity enhancement upto 16 times have been observed. Field enhancement gives rise to enhanced sensitivity. The usefulness of this resonance-enhanced x-ray fluorescence spectrometry in the study of diffusion with marker layers in thin films including polymers and nanocomposites has been elucidated.
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 effects on diffusion coefficient were observed below crystallization temperature of the amorphous phase. In the well-relaxed state, the values of preexponential factor D 0 and activation energy q are given by ln D 0 ϭϪ16.6Ϯ2 m 2 /s and qϭ1.3Ϯ0.2 eV. On the basis of correlation between ln D 0 and q, it is suggested that the mechanism of self-diffusion of iron in amorphous iron nitride is very similar to that in metallic glasses.
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.
Metals and their alloys are highly susceptible to corrosion in wet environment. Dealloying is a p... more Metals and their alloys are highly susceptible to corrosion in wet environment. Dealloying is a particular type of corrosion, attacking practically all metals in industrial use: When an alloy is coming into contact with an electrolyte, the less noble metal may go into solution, typically causing crack formation and subsequent material failure upon stress. We used bulk sensitive Hard X-ray
Nanosized particles of Ni 0.25 Co 0.25 Zn 0.5 Fe 2 O 4 have been synthesized by chemical coprecip... more Nanosized particles of Ni 0.25 Co 0.25 Zn 0.5 Fe 2 O 4 have been synthesized by chemical coprecipitation method. Exchange-bias phenomenon arising from the core-shell interaction has been investigated using a combination of in-field, low-temperature Mössbauer spectroscopy and dc magnetization. To understand the clear mechanism of interaction and exchange bias, isothermal remanence magnetization-dc demagnetization and M-H loops at different cooling field have been taken. The observed variation in coercivity H C and exchange-bias field H E confirms that only core is affected by the cooling field. The slope of the Henkel plot is 1.82, indicating the noninteracting nature of the particles. In-field Mössbauer spectroscopy clearly establishes the core and shell contributions and also confirms that 70% of spins are in the shell. The barrier energy has been estimated to be 17ϫ 10 −14 ergs which accounts for the fact that the shell is not affected by application of as large a field as 5 T.
Nanocomposites with magnetic components possessing nanometric dimensions, lying in the range 1-10... more Nanocomposites with magnetic components possessing nanometric dimensions, lying in the range 1-10 nm, are found to be exhibiting superior physical properties with respect to their coarser sized counterparts. Magnetic nanocomposites based on gamma iron oxide embedded in a polymer matrix have been prepared and characterized. The behaviour of these samples at low temperatures have been studied using Mössbauer spectroscopy. Mössbauer studies indicate that the composites consist of very fine particles of γ γ-Fe 2 O 3 of which some amount exists in the superparamagnetic phase. The cycling of the preparative conditions were found to increase the amount of γ γ-Fe 2 O 3 in the matrix.
Reactive ion-beam sputtering has been used to prepare iron nitride over a wide composition range.... more Reactive ion-beam sputtering has been used to prepare iron nitride over a wide composition range. It is found that the samples deposited at room temperature exhibit amorphous phase in the composition range from 12 at. % nitrogen to 23 at. % nitrogen. For samples deposited at liquid nitrogen temperature the system is amorphous up to 35 at. % nitrogen. Amorphization can be understood in terms of a frustration in the system due to a competition between ␣ and phases. Kinetic constraints are also found to play a role in the amorphization process. Mössbauer measurements suggest that the local order in the amorphous phase consists of a mixture of ␣-Fe-like and-Fe 3 N-like short-range orders. On the iron rich side the amorphous phase exhibits two-step crystallization, with a primary ␣-Fe phase precipitating out in the first step. Around 22 at. % nitrogen the system exhibits a single step isomorphous transformation to phase. Thus, amorphous iron nitride phases exhibit behavior very similar to the conventional transition metal-metalloid amorphous alloys. In the remaining composition range nanocrystalline phases are formed. The amorphous magnetic iron nitride phases are expected to have distinct advantages over their crystalline counterparts in terms of soft magnetic applications.
The mechanism of stress relaxation in nanocrystalline Fe-N thin film has been studied. The as-dep... more The mechanism of stress relaxation in nanocrystalline Fe-N thin film has been studied. The as-deposited film possesses a strong in-plane compressive stress which relaxes with thermal annealing. Precise diffusion measurements using nuclear resonance reflectivity show that stress relaxation does not involve any long-range diffusion of Fe atoms. Rather, a redistribution of nitrogen atoms at various interstitial sites, as evidenced by conversion electron Mössbauer spectroscopy, is responsible for the relaxation of internal stresses. On the other hand, formation of the γ-Fe 4 N phase at temperatures above 523 K involves long-range rearrangement of Fe atoms. The activation energy for Fe self-diffusion is found to be 0.38 ± 0.04 eV.
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.
The occurrence of bulk superconductivity at ~22 K is reported in polycrystalline samples of BaFe ... more The occurrence of bulk superconductivity at ~22 K is reported in polycrystalline samples of BaFe 2-x Ru x As 2 for nominal Ru content in the range of x=0.75 to 1.125. A systematic suppression of the spin density wave transition temperature (T SDW) precedes the appearance of superconductivity in the system. A phase diagram is proposed based on the measured T SDW and superconducting transition temperature (T C) variations as a function of Ru composition. Band structure calculations, indicate introduction of electron carriers in the system upon Ru substitutiom. The calculated magnetic moment on Fe shows a minimum at x=1.0, suggesting that the suppression of the magnetic moment is associated with the emergence of superconductivity. Results of low temperature and high field Mossbauer measurements are presented. These indicate weakening of magnetic interaction with Ru substitution
The effect of Cr substitution into nanocrystalline Co-Zn ferrite prepared by the chemical copreci... more The effect of Cr substitution into nanocrystalline Co-Zn ferrite prepared by the chemical coprecipitation method has been studied. Mössbauer studies at a temperature ͑20 K͒ well below the blocking temperatures of the samples show that Cr goes preferentially into the octahedral B site and that the hyperfine fields at both A and B sites decrease with increase in Cr concentration. Based on the cation distribution obtained from fitting Mössbauer spectra, structural parameters such as lattice parameters, site bond and edge lengths, and the oxygen parameter u have been calculated. The trend of theoretically calculated lattice parameter with Cr content matches well with the experimentally obtained values.
Preliminary results on magnetic and transport properties of a thin film of disordered Fe 2 CrAl d... more Preliminary results on magnetic and transport properties of a thin film of disordered Fe 2 CrAl deposited on (111) Si by pulsed laser deposition is reported in this study. While the bulk arc melted ingot used as target for the deposition is purely ferromagnetic, the film shows the coexistence of different magnetic phases, which arises due to the granular nature of the film. This is because, although the average composition pertains to Fe 2 CrAl, local disorder results in the formation of grains with different magnetic states that may be ferromagnetic or may consist of magnetic clusters. The resulting magnetic inhomogeneity of the thin film leads to large values of negative temperature coefficient of resistance of $22%/K at 260 K.
We have studied the origin of a counter intuitive diffusion behavior of Fe and N atoms in a iron ... more We have studied the origin of a counter intuitive diffusion behavior of Fe and N atoms in a iron mononitride (FeN) thin film. It was observed that in-spite of a larger atomic size, Fe tend to diffuse more rapidly than smaller N atoms. This only happens in the N-rich region of Fe-N phase diagram, in the N-poor regions, N diffusion coefficient is orders of magnitude larger than Fe. Detailed selfdiffusion measurements performed in FeN thin films reveal that the diffusion mechanism of Fe and N is different-Fe atoms diffuse through a complex process, which in addition to a volume diffusion, predominantly controlled by a fast grain boundary diffusion. On the other hand N atoms diffuse through a classical volume-type diffusion process. Observed results have been explained in terms of stronger Fe-N (than Fe-Fe) bonds generally predicted theoretically for mononitride compositions of transition metals.
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.
Electronically mediated sputtering in thin gold films, bombarded with 200-MeV Ag ions, has been o... more Electronically mediated sputtering in thin gold films, bombarded with 200-MeV Ag ions, has been observed by ex-situ thickness measurements of the film using x-ray reflectivity technique. The observed sputter yield depends upon the film thickness and is about 410 atoms per incident ion for films of thickness 150 Å and 235 atoms per incident ion in 450-Å-thick film. This sputtering rate is a few orders of magnitude higher as compared to that normally encountered in the regime of elastic collisions. Reduced mobility of the electrons due to scattering from the surface and the grain boundaries plays an important role in enhancing the effects of electronic excitations. Sputtering is accompanied by a significant smoothening of the film surface and smearing of the boundaries between the grains.
In this work, we studied phase formation, structural and magnetic properties of iron-nitride (Fe-... more In this work, we studied phase formation, structural and magnetic properties of iron-nitride (Fe-N) thin films deposited using high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (dc-MS). The nitrogen partial pressure during deposition was systematically varied both in HiPIMS and dc-MS. Resulting Fe-N films were characterized for their microstructure, magnetic properties and nitrogen concentration. We found that HiPIMS deposited Fe-N films show a globular nanocrystalline microstructure and improved soft magnetic properties. In addition, it was found that the nitrogen reactivity impedes in HiPIMS as compared to dc-MS. Obtained results can be understood in terms of distinct plasma properties of HiPIMS.
In this work we studied Cu/Co multilayers prepared using dc-magnetron sputtering technique with A... more In this work we studied Cu/Co multilayers prepared using dc-magnetron sputtering technique with Ag surfactant. It was found that Ag balances the difference in the surface free energy of Cu and Co and this results in removing the asymmetry in the interface roughness of Cu-on-Co and Co-on-Cu interfaces. As the interfaces become symmetric, we observe a significant enhancement in antiferromagnetic coupling and magneto resistance. Further, a correlation of spin-dependent scattering with the interface roughness is brought by comparing Cu/Co multilayer prepared using different deposition methods. It was found that as interface roughness increases spin-dependent scattering decreases.
Resonance enhancement of x rays in a thin film and fluorescence emission from embedded marker lay... more Resonance enhancement of x rays in a thin film and fluorescence emission from embedded marker layers within the film have been studied. With embedded marker layers of Ti, Fe, and W at different depths in a thin Si film on a Au-coated Si substrate, it has been shown that the position of a marker layer throughout the depth of the film can be unambiguously determined with a precision better than 0.5 nm. In this example, fieldintensity enhancement upto 16 times have been observed. Field enhancement gives rise to enhanced sensitivity. The usefulness of this resonance-enhanced x-ray fluorescence spectrometry in the study of diffusion with marker layers in thin films including polymers and nanocomposites has been elucidated.
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 effects on diffusion coefficient were observed below crystallization temperature of the amorphous phase. In the well-relaxed state, the values of preexponential factor D 0 and activation energy q are given by ln D 0 ϭϪ16.6Ϯ2 m 2 /s and qϭ1.3Ϯ0.2 eV. On the basis of correlation between ln D 0 and q, it is suggested that the mechanism of self-diffusion of iron in amorphous iron nitride is very similar to that in metallic glasses.
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.
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Papers by Ajay Gupta