http://localhost:8081/jspui/handle/123456789/37 Mon, 30 Jun 2025 16:36:14 GMT 2025-06-30T16:36:14Z http://localhost:8081/jspui/handle/123456789/15602 Title: STATISTICAL THERMODYNAMICS OF SYNTHETIC SPIN-ORBITCOUPLED QUANTUM GASES Authors: Gupta, Reena Abstract: Spin-orbit coupling (SOC) gives rise to a large number of interesting condensed matter phenomena such as spin Hall effect, topological insulators, magnetoelectric effects, along with many interesting phenomena in nuclear physics and atomic physics. Ultracold gases of neutral atoms provide an ideal platform to study various such phenomena because of their remarkably controllable environment that can be achieved using laser light. Although a gas of neutral atoms does not possess gauge coupling to the electromagnetic field, there has been a number of theoretical proposals for producing synthetic magnetic field and hence synthetic SOC in neutral atoms. Only one of these, the one-dimensional (11)) equal Rashba-Dresselhaus SOC, has been realized experimentally. In this thesis we present a detailed study of the various thermodynamic properties of synthetic spin-orbit coupled quantum gases. The main purpose of this thesis is to find out how SOC modifies the many-body effects in both uniform as well as trapped gases. This thesis comprises of six chapters. Chapter 1 is an introductory chapter containing a discussion on the thermodynamics of uniform and trapped gases. We also discuss natural SOC in atoms and solids and show how synthetic SOC can be produced in a gas of neutral atoms using atom-laser interaction. In Chapter 2, we have niiade a thorough study of the Weyl-coupled three-dimensional (3D) gas of free bosons and ferinions. It is found that the presence of coupling induces interaction which counters "effective" attraction (repulsion) of the exchange symmetry present in zero-coupling ideal Bose (Fermi) gas. This result is further corroborated by SOC 11 dependence of the isothermal compressibility. Incipient Bose-Einstein condensation (BEC) at very weak coupling has also been reported although the system does not really go in the Bose-condensed phase. Further, our studies show that there exists a dimensional crossover from three dimensions to one dimension at large coupling strength. Study of this Weyl-coupled system after addition of harmonic trapping comprises Chapter 3 of the thesis. We have shown that the phenomenon of BEG, destroyed by the SOC in 3D Bose gas (as discussed in Ch. 2), gets restored by trapping, even in the noninteracting case. Also, we have concluded that the increase in the coupling strength makes the statistical interaction weaker and weaker in trapped gases too and that now the system undergoes dimensional crossover from three to two dimensions. Chapter 4 focuses on the study of two-dimensional (2D) gas of ashbacoupled free bosons under harmonic trapping. We have derived expressions for the various thermodynamic quantities using Kummer's function in conjunction with the polylogarithmic function. We find in this system, dimensional reduction takes place from two dimensions to 1.5. Chapter 5 presents our study on d-dimensional spinorbit coupled system under power-law trapping, where we have obtained expression for density of states (DOS) for both the isotropic and anisotropic couplings in uniform as well as trapped gases. The emergence of even-odd dimensional nonequivalence evinced by SOC induced energy segmentations in the DOS has been analyzed from the point of view of the rotational symmetry. The general conditions involving the dimensionality and the power-law exponent in such systems have then been obtained for the onset of BEG. The summary of our work along with the conclusions and future directions is presented in Chapter 6. Fri, 01 May 2015 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/15602 2015-05-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/15601 Title: STUDY OF 732.0 mu AND 844.6 nm DAYGLOW EMISSIONS UNDER VARYING SOLAR ACTIVITY CONDITIONS Authors: Dharwan, Maneesha Abstract: The Earth WOl1l(l be lifeless without the atmosphere which not only protects the Earth from harmful ra(hation from the Sun but also supports life system by maintaining suitable temperature and warming the surface through heat retention. The Sun-Earth system provides insight to the structure and dynamics of the Earth's atmosphere. The basis of all physical and chemical processes occurring in the Earth's atmosphere is the Sun-Earth interaction. The study of Sun-Earth interaction reqiures acci.irate knowledge of variations in solar radiation and solar wind which is a very challenging task clue to active interaction of solar energy with the atmosphere of the Earth. Different layers of Earth's atmosphere interact with the energy of the Sun in a (hiferent nianner. The atmosphere of the Earth comprises of four layers (lependmg on the vertical structure of the temperature profile [1-3]. These layers are troposphere (0-12 km). stratosphere (12-50 kin), rnesosphere (50-90 kni) and thermosphere (above 90 km). The ionosphere (above 60 krn) is a region of Earth's atmosphere containing large amount of charged atoms and molecules [4-14]. It is not a separate layer but is embeckled in the layers of atmosphere. The Earth's atmosphere can also be broadly classified into three regions. These are lower atmosphere (0-20 km), middle atmosphere (20-100 kin), and upper atmosphere (above I' 100 km). The upper atmosphere is one of the most important part of the Earth's atmosphere since it is the region where solar radiation makes its first contact with the planet Earth. Most of the ionosphere and atmosphere interactions occur in this region. The photoclissociation of N2 and 02 produces 0 and N atoms in abundance. The atomic species are dominated at higher altitudes and the molectilar species are mostly accumulated in the lower (lomnain of the upper atmosphere. The temperature in this region first rises dramatically with the altitude dine to the absorption of solar EUV radiation by oxygen and nitrogen molecules and then becomes constant above 50() km [15]. The solar radiation interacts with different species of the Earth's atmosphere at different wavelengths at all altitudes, energizing these species in terms of ionization. (liSSOCiatiOn and excitation. Almost all of the ultraviolet radiation is absorl)ed in the Earth's atmosphere and is therefore a good proxy to predict the dynamics, temperature distribution and the chemical processes occurring in the upper atmnosphere. There are various measurements and modeling studies reported in the literature on solar UV radiation [16-19]. The interaction of solar UV radiation with the atmospheric species causes specific transitions of some species from lower to higher excitation states. In the upper atmosphere, which has a low density and is optically thin for the radiations above 350 urn, these species may dc-excite to lower energy states by elmtting radiations. These emitted radiations constitute a very wide range of emission spectrum known as 'airgiow' . Airglow emissions are (lassifiedl into three types based on the time of observation. These are dayglow. nightglow and twilight glow. When the observations are taken during the day time it is dayglow. The dayglow emissions are difficult to observe due to high solar background. The nightglow is observed during the night time. The twilight glow is observed during early morning or early evening when the Sun is below the horizon but is seen from altitudes above 50 km. The airgiow emission line structure and intensity provide wealth of information 111 about the composition and temperature of the atmosphere and the doppler shifts give information about the wind motions. The structure and (lynaimcs of gravity, planetary and tidal waves can be studied using airglow emissions [20-22]. The airglow features are used to retrieve ozone concentration in the upper mesosphere and lower thermosphere [23]. The rotational temperatures could be easily traced out from airglow emission features [24,25]. The effects of geomagnetic storms on airglow emissions have been studied by various researchers [26-28]. Thus for a complete overview and understanding of the Earth's atmosphere airglow emission studies play a vital role. The airglow emission arising due to molecular species occurs in the altitude range of 80-270 km since dissociation is (lormnant above 100 kin while the density of the species decreases with altitude. The airglow emissions arising due to atomic species occur in the altitude range 80-1000 kin. Thus airglow is generated by different species at different altitudes [29-32]. The most important ones are those generated by atomic and molecular oxygen and nitrogen, OH molecule, and Na atoms [33-36]. The atomic oxygen generated 557.7 urn, 630.0 run, 732.0 mn and 844.6 nm airglow emissions are of much interest to the researchers due to the valuable information provided by these emissions [30,37-45]. The 557.7 mu (green line) airglow emission occurs in rarefied gaseous media al)ove 90 kin altitude involving transition between metastable states O('S-'D). The green line airglow emission involves a lot of complex chemistry and tracing out accurate atomic oxygen number density from this emission is difficult. However, this emission is a good indicator of wind dynamics and horizontal diffusion [46-48]. The 630.0 nm airglow emission arises at the F2 ionospheric layer altitudes and is a good tracer of neutral wind fields and vertical temperatures in the upper atmosphere [49, 501. This emission results from a metastable state 0(1 D) which involves various photocliernical production processes and loss mechanisms. Hence, tracing of the atomic oxygen number density is a complicated procedure .Above 200 kin altitude the reliable knowledge of atomic oxygen number density becomes iv essential to track the satellite drag and to predict the space weather conditions. The satellite passing through the Earth's upper atmosphere experiences drag force which depends upon density at the satellite altitude. The 732.0 urn airgiow emission dominates above 200 km which arises from the transition from metastable state 0(2 P-2D). The 0(2P) is produced through photoionisation excitation of ground-state atomic oxygen and photoelectron impact ionisation of ground-state atomic oxygen [44,51,52]. Consequently, the production rate of 732.0 nm emission would strongly depend upon the atomic oxygen number density. A number of researchers have found that the O+(2P) 732.0 nm airglow emission proves to be a potent tool to predict thermnospheric density above 200 km altitude [52,53]. A limited number of studies have been reported in the literature to infer solar UV fluxes and the exospheric temperatures from 732.0 urn airgiow emission [54-561. Another important emission effective in investigating the atomic oxygen number density in the altitude range 130-260 km is the 844.6 nm airgiow emission since it arises from allowed transition and hence no loss mechanism processes involve in the modeling tecimiques. Therefore, 844.6 nm airglow emission serves as a direct measure of atomic oxygen concentration [57. 58]. A very limited number of measurement studies have been reported on 732.0 nm and 844.6 urn airgiow emissions in the literature [39,44,52-55,57,59-61]. Although few modeling studies have been clone on 732.0 nrn and 844.6 urn airgiow emissions, but these could not be validated due to lack of experimental data on parameters such as reaction rate coefficients, transition probabilities, collisional cross sections etc. However, the data on these parameters is still limited. Therefore, the existing models of 732.0 urn and 844.6 urn day-glow emissions need to be modified in the light of recently revised reaction rate coefficients, transition probabilities and collision cross sections. In the present thesis an attempt is made to study 732.0 urn and 844.6 urn (layglow emissions by means of mnocleling by incorporating latest transition probabilities, reaction rate coefficients and cross sections. The solar extreme ultraviolet (EUV) fluxes calculated using the Solar Irradiance Platform (SIP) are incorporated into the model [62.63]. The neutral atmospheric parameters are adopted from the Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Exosphere (NRLMSISE-00) model. The ionospheric parameters are adopted from the International Reference Ionosphere (IRI-07) model. The photochemical models of 732.0 nm and 844.6 nm dayglow emissions are further used to study these emissions under various solar and geomagnetic activity conditions. The research work presented in this thesis is summarized in the form of five chapters. The first chapter gives the general introduction to the Sun-Earth interaction, solar radiation, airglow emissions, and topics related. It outlines the need and importance of studying airglow emissions. A brief literature survey of the earlier studies in this field in context to the present study is presented. The importance of the present problem and the reason for choosing the same are also presented in this chapter. In the second chapter, the development of a photochemical model of 732.0 nm dayglow emission is discussed using latest updated transition probabilities, reaction rate coefficients and cross sectionis. The measurements as provided by instruments oriboard Atmosphere Explorer-C satellite, Dynamics Explorer-2 spacecraft and Upper Atmosphere Research Satellite are used to validate the model results. It has been found that the emission rates conhl)l.itedl using the present model are in good agreement with the measurements. It is also found that the present model results are in better agreement with the measurements in comparison with the earlier models. The model results show that the updated rate coefficients and transition probabilities are quite consistent with each other and may be used in the aeronomical studies. In the third chapter, the effect of atomic oxygen abundance on the voli.uiie emission rate of 732.0 urn dayglow emission at the equator for edluinox and solstice cases vi is discussed. To study the effect of atomic oxygen abundance on 732.0 rim (layglow emission, the atomic oxygen number densities obtained from the NRLMSISE-00 model are increased (or decreased) in an increment (or decrement) of 20% and are incorporated into the photochemical model to compute volume emission rate profiles. The present study shows that the peak emission rate (PER) varies linearly below the reference level of atomic oxygen number density and does not vary linearly above the reference level of atomic oxygen number density. The atomic oxygen number density at reference level corresponds to that value which is obtained from the NRLMSISE-0() model. It is found that the altitude of peak emission rate moves upward as the F10.7 solar index increases. On an average the upward movement of altitude of PER is about 9 kni for both the equinox and solstice cases. The upward movement of the altitude of peak emission rate is clue to the enihamicemnienit in atomic oxygen number density with increase in F10.7 solar index. In the fourth chapter, the effect of geomagnetic storms on 0+(2p.2D) 732.0 nrn dayglow emission is studied. Three geomagnetic storms which occurred on 23-27 August 2005, 13-17 April 2006 and 1-5 February 2008 are chosen in the present study. A negative correlation is found between the volume emission rate (VER) and the Dst index for all the three geomagnetic storms. The present study shows that the relative variation of VER with respect to the initial value of VER (before the onset of a geomagnetic storm) during the main phase increases above 260 km. It is also found that the altitude of the peak emission rate does not show any appreciable variation with the activity of geomagnetic storm. A positive correlation is found between the zenith intensity and the atomic oxygen number density. The atomic oxygen number density obtained from NRL1SISE-0() model is compared with the measurements of Earle et al. [26] during a geomagnetic storm. This cornparison shows that the atomic oxygen number density is provided by NRLMSISE- 00 model is significantly lower than the measured value. Consequently, the atomic vii oxygen number density is treated as a variable parameter in the photochemical model and its effect on the VER of 732.0 run dayglow emission is further studied. The zenith intensity is found to increase about 70% even in the case of weakest storm when the atomic oxygen number density is doubled. In the fifth chapter, a photochemical model is developed to study 844.6 nm dayglow emission. The Solar2000 EUV (Extreme UltraViolet) flux model, neutral atmosphere model (NRLMSISE-00) and latest available cross-sections are incorporated in this model. The present model is used to study the effects of geomagnetic storm on the 844.6 urn dayglow emission at a low latitude station Tirunelveli (8.7°N, 77.8°E). Three geomagnetic storms which occurred during 23-27 August 2005, 13-17 April 2006 and 1-5 February 2008 are chosen in the present study. It is found that the volume emission rate (VER) shows a negative correlation with the Dst index for all the three geomagnetic storms. The present study also shows that the altitude of the peak emission rate does not vary with the activity of geomagnetic storm. The model predicts a positive correlation between the zenith intensity of 844.6 nm dayglow emission and atomic oxygen number density. It is reported by Dharwan et al. [60] that the atomic oxygen number density given by NRLMSISE- 00 model is significantly lower than the measured values. Consequently, the effect of atomic oxygen number density abundance on 844.6 nrn dayglow emission is further studied by treating the atomic oxygen number density as a varial)le parameter in the present model. An increase of more than 50% in the zenith intensity above the normal level (before the onset of the storm) is found when the atomic oxygen number density which is obtained from NRLMSISE-00 model is doubled (under the limits of measurements). A comparative study of 732.0 nm and 844.6 urn dayglow emission under geomagnetic storm conditions is also carried out for the above mentioned geomagnetic storms. The study shows that there is an increase of 10% - in the ratio of VERs of the two emissions (VER514(i/VER7320) for the intense storm and around 7% for the weakest storm during the main phase at 260 km. The ratio of zenith intensity of the two emissions (I846/I7:320) is more or less constant during all the phases of the storm in all the three cases. Tue, 01 Dec 2015 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/15601 2015-12-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/15600 Title: DESIGN OF LONG PERIOD WAVEGUIDE GRATING DEVICES USING NATURAL OPTIMIZATION ALGORITHMS Authors: Semwal, Girish Abstract: The invention of LASER revolutionized new research in the area of optics and telecommunication. The LASER is a coherent light source which produces the monochromatic, high intensity and directional optical beam. Initially the optical phenomena were studied with the bulk optical material using LASER. The techniques of the prism and grating coupling have been evolved for the coupling of light into thin films. Subsequent research improved the coupling efficiency of light into thin Mills. The optical phenomena of bulk materials were investigated with the thin film of dielectric materials. The wavelength of light is small: hence the micron order film can guide the light from one place to other place. The specific devices can be designed by controlling the parameters of a waveguide. The devices based on the thin film may be placed close to one another on the single substrate and thin films can also work as interconnect for the thin film photonics devices. A large number of optical devices can be fabricated on the single chip for optical signal processing. The concept for integrated optical devices evolved similar to the integrated circuits and hence the analogous name, integrated optics (10) was suggested. Planar vaveguide is a simpler and effective thin film photonics structure. The advanced photonics devices are designed using the complex multilayer planar structure. The material like glass was primarily used for the fabrication of thin film devices. Only passive devices can be fabricated using glass material. Dielectric material like lithium niobate (LiNb03) is superior for the fabrication of active devices. Semiconductor materials like silicon and gallium arsenide (GaAs) are also preferred in the integrated optics. The advantage of using semiconductors in 10 is that the source and detectors can be libricated on the same substrate along with the optical devices. The source and detectors requires some electronics circuit such as laser diode driver for source and amplifiers circuits of detector. These electronics circuits can be easily fabricated on the same integrated chip. The semiconductor technology is sufficiently mature. Hence the advantages of fabrication technologies in the semiconductor devices are much useful in the 10 technology. Another class of material is the polymer used in integrated optics. The polymer is a low cost material. The polymers are suitable material for the Abstract development of 10 sensors. The poor shelf life and large temperature coefficient are the biggest disadvantages of polymers which restrict their use in the optical communication. The accuracy of planar waveguide devices depends on the accuracy of the design parameters of waveguide structure. The analysis of simple three layers symmetric and asymmetric guided structure can be analyzed by solving the transccndcntal equation numerically. The complex multilayer structure requires the accurate and efficient numerical techniques to solve the structure in conjunction with superior computational power. Various numerical techniques have been proposed to compute the modes of a multilayer planar waveguide with the advancement of the computer. Numerical methods such as the semi-analytical-graphical method, iterative method, reflection pole and vector density method, variational method. APM based methods have been used to solve the planar waveguide. Every numerical method used for the design of planar waveguide device has its advantages and disadvantages; hence the suitable choice of numerical technique is important for the design and analysis process. (:vlindrical waveguide has been developed for long distance optical communication called the optical fiber. It is an equivalent to the coaxial cable used as communication medium in microwave communication. Initially, the extensive study of light propagation. signal losses and pulse dispersion in the fiber has been carried out to improve the signal quality. Later. a phenomenon of photosensitivity in the germanium doped fiber was observed by Hill in 1978. In the subsequent years. the photosensitivity has been utilized to develop the fiber Bragg grating (FBG). The fiber grating devices have been extensively used for the telecommunication and sensing technologies. The later version of grating was incarnated as long period grating (LPG). The LPG has the advantages of easy fabrication technology, simple alignment and low cost. Fiber gratings have limitations due to selection of material and geometry. Optical fiber is made of silica and has cylindrical geometry. Tailoring of application specific complicated rejection band spectrum in fiber grating is limited due to material and geometrical constrains. LPG in a four layer planar waveguide was proposed to overcome the limitations of fiber gratings and to increase the degrees of freedom in the design process. The grating is popularly known as the long period waveguide grating (I.PWG). In recent years, large number of designs based on the LPWG have been proposed and their fabrication as well as characterization has been demonstrated. LPWG generates the symmetric resonance rejection band; however the application Abstract specific spectra are asymmetric. Such rejection band spectra can be obtained using the complex waveguide and grating structures. The complex design of LPWG requires an optimization process to optimize the grating and waveguide parameters for achieving application specific complicated rejection band spectra. The optimization techniques such as Lagrange multiplier optimization, genetic algorithm (GA) and particles swarm optimization (PSO) have been implemented for FBG and LPFG devices. Only limited number of grating parameters have been optimized in fiber gratings. The LPWGs possess large degree of freedom due to multilayer structure and freedom of selecting material. The studied of propagation constants and modal fields of the mode of a complex planar waveguide are also required for generating rejection band spectra besides the optimized grating parameters. The application specific target spectrum can be obtained by suitable combination of the grating and waveguidc parameters including the waveguide material. In this thesis we have proposed an efficient mode computation method for multilayer planar waveguide followed by two optimization techniques GA and adaptive PSO; as the efficient tools for optimizing LPWG parameters. Different types of LPWG in planar waveguide structure have been optimized to obtain the application specific pre-defined target spectra. Ihe thesis presents a robust and reliable method for the computation of propagation constants and modal field distributions in a variety of multilayer planar waveguide structures. A technique to solve generalized dispersion equation of multilayer planar waveguide has been demonstrated to obtain all the expected guided modes. The dispersion equation for the guided structure has been solved using bisection method in conjunction of mode identification technique and domain decomposition for isolating the modes. The complex multilayer structures cannot be solved with the bisection method hence a new method has been proposed. The solution of dispersion equation for the complex structure is based on the derivative free method for computing the roots of an analytical function in complex plane. The derivative free method extracts the roots which are very close to actual zeros of the dispersion function. Roots are further refined using the robust iteration method to achieve the desired accuracy. Application of the proposed method has been verified by solving the modes of a variety of structures including lossless structure, leaky structure, quantum well waveguide, active waveguide, non-linear waveguide. ARROW waveguide. Metal clad waveguide, large-core leaky structure and coupled-core waveguide. The method is efficient and computes all modes of planar waveguide with sufficient accuracy. Abstract A tour-layer planar waveguidc has been used to design LPWG. LPWG has numerous applications in the optical communication and sensing technologies. LPWG has been design by embedding corrugated grating in the film of waveguide. The modes of the waveguide have been computed by the method developed in the present thesis. Global optimization properties of genetic algorithm (GA) have been utilized to design LPWG devices for the application specific spectra. Pre-defined target spectra corresponding to single-band. wide-band and dual-band rejection have been considered. The optimized grating parameters of corrugated grating have been obtained using GA optimization to achieve these target spectra. Three parameters namely the grating length, grating period and corrugation height of LPWG have been optimized using GA optimization. The simulation results show that the method is easy to implement and useful to design the grating for a pre-defined application specific spectra. LPWG has large degree of freedom due to selection of materials and geometry. lIence. the complex structure can he tailored to generate the complex rejection band spectra. Complexity of' design introduces the large number of design parameters. GA is an efficient method for optimization and performs well for the small number of' optimization parameters. The GA optimization becomes slow as the number of parameters increase in the optimization process. Sometimes the process of optimization is stuck and the optimization process is trapped in the local minima with increased number of parameters. In such a case, an efficient optimization method has been explored. To address this. we have presented the design optimization of LPWG based wavelength filters using adaptive particle swarm optimization (APSO) technique. Convergence analysis of APSO algorithm with single-band, wide-band and dual-band rejection filters has been demonstrated first. These filters have been designed in four layer planar waveguide structure with corrugated grating embedded in the guiding film. Afler convergence tests of algorithm, the optimization technique has been implemented to design LPWG for more complicated application specific filters. The modified complex waveguide structure has been used to generate such complex rejection band filters. Four-layer waveguide structure has been modified by segmenting the cladding into two parts. Each part has same cladding thickness but differs in refractive index. Optimization of grating length of two sections, grating period, corrugation height, cladding thickness and refractive index difference of two cladding section has been carried out to design wavelength filters for achieving a desired target spectrum. iv A bstrac Rectangular rejection band filter, filters for flattening the ASE of FDFA and gain of EDWA has been designed successfully using segmented cladding LPWG. Another design we have optimized in this thesis has two concatenated gratings on the same substrate. Two sections of grating have different lengths, periods, corrugation heights but have the same cladding profile. 'l'otal seven numbers of LPWG parameters have been optimized to achieve various application specific and asymmetric rejection band spectra. Design procedure of the LPWG to generate the rectangular target spectrum has been demonstrated first with APSO. The technique has been extended to optimize the complicated grating structure to generate the asymmetric target spectra. Finally, the design optimization has been illustrated by various examples including filter for flattening the ASE spectrum of' lE)FA and gain flattening filter for LI)WA. The optimization process f'or simple LPWG, segmented cladding LPWG structure and LPWG with a pair of' two concatenated grating has been successfully demonstrated. Apart from these, we have also carried out the optimization in more complex structure namely five-layer plasmon waveguide. The plasmon waveguide is widely used in biomedical applications and in the biological and chemical warfare agent detection. Grating assisted surface plasmon resonance (SPR) waveguides are used as efficient refractive index sensors. APSO has been used to optimize the waveguide and grating parameters of grating assisted SPR sensors. We have considered two waveguide structures in the design optimization process, and the grating and the waveguide parameters have been optimized to achieve the desired results. l'otal five parameters of waveguide and gratings have been optimized. The designed sensors show extremely good sensitivity of grating assisted SPR refractive index sensors. Finally, we conclude the work carried out in the thesis and propose the outlook of' future work. Sun, 01 Nov 2015 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/15600 2015-11-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/15599 Title: SYNTHESIS AND CHARACTERIZATION OF Ni-Mn-X (X: In, Sb) FSMA THIN FILMS Authors: Akkera, Harish Sharma Abstract: In recent years, Ni-Mn-X (X: In, Sb) based ferromagnetic shape memory alloys (FSMAs) showing a reversible first-order martensitic phase transformation between high symmetry austenitic phase to low symmetry martensitic phase accompanied with a macroscopic shape change, have attracted increasing scientific attention as multifunctional materials due to their large magnetic-field-induced strains (MFIS) by the rearrangement of twin variants in the martensite and as potential candidates for high sensitivity magnetic actuators and sensors. These alloys exhibit various magnetic field-driven properties such as magnetic shape memory effect, martensitic phase transformation, exchange bias effect and magnetocaloric effect etc. So far, numerous groups have studied these magnetic field-driven properties in bulk FSMAs. For emerging micro devices such as magnetically driven microelectromechanical systems (MEMS) and even microscopic machines, high quality FSMA thin films grown on semiconductor substrates are required. It is desirable to establish the process for producing high quality thin films of these materials for their integration into emerging technologies. The main objective of the present work was to synthesize nanostructured ferromagnetic shape memory alloy thin films of Ni-Mn-X (X: In, Sb) on Si (100) substrate using DC magnetron sputtering technique to investigate the structural, phase transformation, magneticand mechanical properties of these films. In addition Ni-Mn-Sb/CrN heterostructures were fabricated and the effect of varying thickness of CrN layer on various properties of heterstructure was studied. A chapter - wise summary of the thesis is given below: Chapter 1 gives an overview of ferromagnetic shape memory alloys and material background. This chapter includes literature survey on physical properties of Ni-Mn-X (X: In, Sb) ferromagnetic shape memory alloys and their thin films. The fourth element addition, exchange bias and magnetocaloric effect properties of FSMAs have been discussed. Chapter 2 presents the details of experimental techniques, which we have used for the synthesis and characterization of these films. The synthesis of thin films in present thesis has been carried out by DC magnetron sputtering technique. Various sputtering parameters were optimized in order to obtained good quality FSMA films. X-ray diffraction technique has been used for phase identification and crystallite size analysis. The surface morphology and microstructure of thin films were studied using Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM). The film thickness was measured using cross-sectional FESEM. The temperature and field dependent magnetization (M-T and M-l-1) measurements of thin films were studied using Cryofree Vibrating Sample Magnetometer (VSM) and SQUID. The electrical properties of these films were measured using four probe resistivity set up in the temperature range from 30 K to 400 K. The nanoindentation was used to study the mechanical properties such as hardness (H), elastic modulus (E), plasticity index (I-lIE) and resistance to plastic deformation (II 3IE2) of thin films. Chapter 3 describes the growth and characterization of nanostructured Ni-Mn-In ferromagnetic shape memory alloy thin films. In this chapter the influence of film thickness on structural, magnetic, electrical and mechanical properties of nanostructured Ni-Mn-In thin films was studied. The film thickness was varied from - 90 nm to 655 nm.XRD analyses revealed that the films exhibit austenitic phase with 1-21 structure at room temperature. The grain size and crystallization extent increased with corresponding increase in film thickness. The temperature dependent magnetization and electrical measurements demonstrated the absence of phase transformation in the film with lower thickness - 90nm which could be due to small grain size of film. For thickness greater than 153 nm, the films show first order martensitic phase transition with thermal hysteresis width, which increases with further increase in film thickness. The field dependent magnetization curves also show the increase in saturation magnetization (SM). The value of refrigeration capacity (RC) which is an important figure of merit has been found to be 155.04 mJ/cm3. Maximum exchange bias of 0.0096 T and large magnetic entropy change AS 1 =l5.2 mJ/cm3 K (field 2 T) at martensitic transition was obtained for film thickness of 655 ni-n which makes them useful for microelectromechanical systems (MEMS) applications. Further, nanoindentation studies revealed the higher values of hardness of 7.2 GPa and elastic modulus of 190 GPa for the film thickness of 153 nm. These findings indicate that the Ni-Mn-In thin film is potential candidate for various multifunctional properties. Chapter 4 describes the growth and characterization of Ni-Mn-Sb-Al and Ni-Mn-In-Cr FSMA thin films. This chapter has been divided into two sections. The first section (section 4.1) describes the effect of aluminium (Al) content on the martensitic transformations and magnetocaloric effect (MCE) in Ni-Mn-Sb ferromagnetic shape memory alloy (FSMA) thin films. An increase in mnartensitic transformation temperature (TM) with increasing Al content was observed from magnetic (M-T) and electrical (R-T) measurements. From the study of isothermal magnetization (M-H) curves, a large magnetic entropy change (ASi4 of 23 1-fiJ/cm3 K was found in N49 gMn32 97A1443Sbl2 8. A remarkable enhancement of MCE has been attributed to the significant change in the magnetization of Ni-Mn-Sb films with increasing Al content. Furthermore, a high refrigerant capacity (RC) was observed in Ni-Mn-Sb-Al thin films as compared to pure Ni-Mn-Sb. The substitution of Al for Mn in Ni-Mn-Sb thin films with field iv induced MCE are potential candidates for micro length scale magnetic refrigeration applications where low magnetic fields are desirable. Section 4.2 describes the influence of Cr addition on the structural, magnetic, and mechanical properties as well as magnetocaloric effect for magnetron sputtered Ni-Mn-In ferromagnetic shape memory alloy thin films. X-ray diffraction studies revealed that Ni-Mn-In-Cr thin films possessed purely austenitic cubic L21 structure at lower content of Cr, whereas higher Cr content, the films exhibited martensitic structure at room temperature. The temperature-dependent magnetization (M-T) and resistance (R-T) results confirmed the monotonous increase in martensitic transformation temperatures (TM) with the addition of Cr content (0 - 4.5 at %). Further the addition of Cr content significantly enhanced the hardness (28.2+2.4 GPa) and resistance to plastic deformation H3/E2 (0.261) in Ni504Mn34.961n13.56CrI.08 film as compared with pure Ni-Mn-In film, which could be due to reduction in grain size, and has been explained in terms of the grain boundary strengthening mechanism. Further, from the study of isothermal magnetization (M-l-l) curves, the magnetocaloric effect (MCE) around the martensitic transformation has been investigated. The magnetic entropy change ASt.i of 7.0 mi/cm3 K was observed in Ni5 I . I Mn3491n9.5Cr4.5 film at 302 K in an applied field of 2 T. Finally, the refrigerant capacity (RC) was also calculated for all the films in an applied field of 2 T. Chapter 5 describes the deposition ofNisoMn368Sbl32/CrN heterostructure thin films on Si (100) substrate to improve the exchange bias and mechanical properties of Ni-Mn-Sb ferromagnetic shape memory alloy thin films. The anti ferrom agneti c CrN thickness was varied from 15 nm-80 nm. The shift in hysteresis loop up to 51 Oe from the origin was observed at 10 K when pure Ni-Mn-Sb film was cooled under a magnetic field of 0.1 T. The observed exchange bias has been attributed to the coexistence of anti ferromagnetic (AFM) and ferromagnetic (FM) exchange interactions in the martensitic phase of the film. On the other hand, a significant shifting of hysteresis loop was observed with AFM CrN layer in Ni5oMn36.8Sb132/CrN heterostructure. The exchange coupled 140 nrn Ni5oMn368Sb13.2/35nm CrN heterostructure exhibited relatively large exchange coupling field of 138 Oe at 10 K compared to other films, which could be due to uncompensated and pinned AFM spins at FM-AFM interface and different AFM domain structure for different thicknesses of CrN layer. Further nanoindentation measurements revealed the higher values of hardness and elastic modulus of about 12.7±1.25 - GPa and 179±0.12 GPa in Ni50Mn36.gSbI3.2/CrN heterostructures making them promising candidate for various multifunctional MEMS devices. Chapter 6 presents the summary and conclusion of the entire work presented in the thesis and also proposes the future directions in which these studies can be extended. Sat, 01 Aug 2015 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/15599 2015-08-01T00:00:00Z