A study of electromagnetic shielding properties of Ni79Fe16Mo5/copper films

The plane wave electromagnetic interference (EMI) shielding properties of DC sputtered Ni79Fe16Mo5 and copper layers were studied according to ASTM D 4935-89 on frequency range of 50 MHz – 2.5 GHz and RF magnetic shielding effectiveness by shielded magnetic loop probes. Results show that Ni79Fe16Mo5 provides better RF magnetic shielding above the layer thickness of approximately 120 nm. Copper provides better plane wave shielding effectiveness. The effect of shield internal interfaces was studied by depositing thin multilayer structures with and without a dielectric spacer layer.

Syntheses of niobium oxide in the presence of magnetic field and determination of physical properties

Now when the technology fast developing it is very important to control the formation of materials with better properties. In the scientific literature there is a number of works describing the influence of magnetic field on the properties and process of formation of materials. The goal of this master's thesis is to analyze the process of electrochemical synthesis of niobium oxide in the present of magnetic field, to compare properties of formed oxide films and to estimate the influence of magnetic field on the process and on the result of synthesis.

Microcracks and Vortices in Superconducting Thin Films

In this work, superconducting YBa₂ Cu₃O_6+x (YBCO) thin films have been studied with the experimental focus on the anisotropy of BaZrO₃ (BZO) doped YBCOthin films and the theoretical focus on modelling flux pinning by numerically solving Ginzburg- Landau equations. Also, the structural properties of undoped YBCO thin films grown on NdGaO₃ (NGO) and MgO substrates were investigated. The thin film samples were made by pulsed laser ablation on single crystal substrates. The structural properties of the thin films were characterized by X-ray diffraction and atomic force microscope measurements. The superconducting properties were investigated with a magnetometer and also with transport measurements in pulsed magnetic field up to 30 T. Flux pinning was modelled by restricting the value of the order parameter inside the columnar pinning sites and then solving the Ginzburg-Landau equations numerically with the restrictions in place. The computations were done with a parallel code on a supercomputer. The YBCO thin films were seen to develop microcracks when grown on NGO or MgO substrates. The microcrack formation was connected to the structure of the YBCO thin films in both cases. Additionally, the microcracks can be avoided by careful optimization of the deposition parameters and the film thickness. The BZO doping of the YBCO thin films was seen to decrease the effective electron mass anisotropy, which was seen by fitting the Blatter scaling to the angle dependence of the upper critical field. The Ginzburg-Landau simulations were able to reproduce the measured magnetic field dependence of the critical current density for BZO doped and undoped YBCO. The simulations showed that in addition to the large density also the large size of the BZO nanorods is a key factor behind the change in the power law behaviour between BZO doped and undoped YBCO. Additionally, the Ginzburg-Landau equations were solved for type I thin films where giant vortices were seen to appear depending on the film thickness. The simulations predicted that singly quantized vortices are stable in type I films up to quite large thicknesses and that the size of the vortices increases with decreasing film thickness, in a way that is similar to the behaviour of the interaction length of Pearl vortices.

Magnetization studies of polystyrene/multiwall carbon nanotube composite films

Lappeenranta University of Technology School of Technology Technical Physics Evgenii Zhukov MAGNETIZATION STUDIES OF POLYSTYRENE/MULTIWALL CARBON NANOTUBE COMPOSITE FILMS Master’s thesis 2015 55 pages, 41 pictures, 9 Tables. Examiners: Professor Erkki Lähderanta D.Sc. Ivan Zakharchuk Keywords: polystyrene, multi-walled carbon nanotubes, MWCNT, composite, magnetization, SQUID. In this thesis magnetic properties of polystyrene/multiwall carbon nanotube (MWCNT) composites are investigated with Quantum Design SQUID magnetometer (MPMS XL). The surface of the composite films is studied via BRUKER Multimode 8 Atomic Force Microscope, as well. The polystyrene/MWCNT composites have been prepared by the group of professor Okotrub (Physics Chemistry of Nanomaterials laboratory, Nikolaev Institute of Inorganic Chemistry, Russia). The composite films have been prepared by solution processing and stretching method. The approximate length and inner diameter of the MWCNTs used in fabrication are 260 μm and 10 nm, respectively. The content of MWCNTs is 1 and 2.5 contents percent (wt%) for studied samples. The stretching of the samples is 30% for samples with 1 and 2.5 wt% content, and one sample with 1 wt% loading of MWCNTs is 100% stretched. MWCNTs aligned perpendicular to a silicon substrate are used as a reference sample. The magnetization field dependencies of the samples exhibit hysteresis behavior. The values of saturation magnetization of composite films are much less compared to that of the reference sample. The saturation magnetization coercitivity field value drops with decrease of MWCNT content. At high magnetic fields strong presence of diamagnetism is observed. Measurements in magnetic field parallel and perpendicular to the composite plate display anisotropy with respect to the direction of stretching. Temperature dependences of magnetization for all samples display difference between zero-field cooled and field-cooled curves of magnetization. This divergence confirms the presence of magnetic interactions in the material. The atomic force microscopy study of the composites’ surfaces revealed that they are relatively smooth and the nanotubes are aligned with the axis of stretching to some extent. 

The Role of Structural Imperfections in Sr2FeMoO6 Thin Films

In this work, Sr2FeMoO6 (SFMO) thin films were studied with the main focus on their magnetic and magneto-transport properties. The fabrication process of pulsed laser deposited SFMO films was first optimized. Then the effects of strain, film thickness and substrate were thoroughly investigated. In addition to these external factors, the effect of intrinsic defects on the magnetic properties of SFMO were also clarified. Secondly, the magnetoresistivity mechanims of SFMO films were studied and a semiempirical model of the temperature dependence of resistivity was introduced. The films were grown on single crystal substrates using a ceramic target made with sol-gel method. The structural characterization of the films were carried out with X-ray diffraction, atomic force microscopy, transmission electron microscopy and high kinetic energy photoelectron spectroscopy. The magnetic properties were measured with SQUID magnetometer and the magneto-transport properties by magnetometer with a resistivity option. SFMO films with the best combination of structural and magnetic properties were grown in Ar atmosphere at 1050 °C . Their magnetic properties could not be improved by the ex situ post-annealing treatments aside from the treatments in ultra-high vacuum conditions. The optimal film thickness was found to be around 150 nm and only small improvement in the magnetic properties with decreasing strain was observed. Instead, the magnetic properties were observed to be highly dependent on the choice of the substrate due to the lattice mismatch induced defects, which are best avoided by using the SrTiO3 substrate. The large difference in the Curie temperature and the saturation magnetization between the SFMO thin film and polycrystalline bulk samples was connected to the antisite disorder and oxygen vacancies. Thus, the Curie temperature of SFMO thin films could be improved by increasing the amount of oxygen vacancies for example with ultra-high vacuum treatments or improving the B-site ordering by further optimization of the deposition parameters. The magneto-transport properties of SFMO thin films do not follow any conventional models, but the temperature dependence of resistivity was succesfully described with a model of two spin channel system. Also, evidences that the resistivity-temperature behaviour of SFMO thin films is dominated by the structural defects, which reduce the band gap in the majority spin band were found. Moreover, the magnetic field response of the resistivity in SFMO thin films were found to be superposition of different mechanisms that seems to be related to the structural changes in the film.

Study of colossal magnetoresistance and pressure effects in La2/3Ca1/3MnO2 thin films /

The main purpose of this thesis is to study properties of La2/3Cai/3Mn03, both polycrystalline ceramics and thin films. This material has striking related electrical and magnetic properties. Thin films show colossal negative magnetoresistance (CMR) near transition from an insulating to a metallic state accompanied closely by transition from a paramagnetic to a ferromagnetic state. The double exchange mechanism (DE) and the Jahn-Teller deformations play an important role in CMR effect. Applied pressure has a very similar effect as does an applied magnetic field, except, at low temperatures (T

Plasma Polymerised Organic Thin Films-A Study on the Structural, Electrical and Nonlinear Optical Properties for Possible Applications

This proposed thesis is entitled “Plasma Polymerised Organic Thin Films: A study on the Structural, Electrical, and Nonlinear Optical Properties for Possible Applications. Polymers and polymer based materials find enormous applications in the realm of electronics and optoelectronics. They are employed as both active and passive components in making various devices. Enormous research activities are going on in this area for the last three decades or so, and many useful contributions are made quite accidentally. Conducting polymers is such a discovery, and eversince the discovery of conducting polyacetylene, a new branch of science itself has emerged in the form of synthetic metals. Conducting polymers are useful materials for many applications like polymer displays, high density data storage, polymer FETs, polymer LEDs, photo voltaic devices and electrochemical cells. With the emergence of molecular electronics and its potential in finding useful applications, organic thin films are receiving an unusual attention by scientists and engineers alike. This is evident from the vast literature pertaining to this field appearing in various journals. Recently, computer aided design of organic molecules have added further impetus to the ongoing research activities in this area. Polymers, especially, conducting polymers can be prepared both in the bulk and in the thinfilm form. However, many applications necessitate that they are grown in the thin film form either as free standing or on appropriate substrates. As far as their bulk counterparts are concerned, they can be prepared by various polymerisation techniques such as chemical routes and electrochemical means. A survey of the literature reveals that polymers like polyaniline, polypyrrole, polythiophene, have been investigated with a view to studying their structural electrical and optical properties. Among the various alternate techniques employed for the preparation of polymer thin films, the method of plasma polymerisation needs special attention in this context. The technique of plasma polymerisation is an inexpensive method and often requires very less infra structure. This method includes the employment of ac, rf, dc, microwave and pulsed sources. They produce pinhole free homogeneous films on appropriate substrates under controlled conditions. In conventional plasma polymerisation set up, the monomer is fed into an evacuated chamber and an ac/rf/dc/ w/pulsed discharge is created which enables the monomer species to dissociate, leading to the formation of polymer thin films. However, it has been found that the structure and hence the properties exhibited by plasma polymerized thin films are quite different from that of their counterparts produced by other thin film preparation techniques such as electrochemical deposition or spin coating. The properties of these thin films can be tuned only if the interrelationship between the structure and other properties are understood from a fundamental point of view. So very often, a through evaluation of the various properties is a pre-requisite for tailoring the properties of the thin films for applications. It has been found that conjugation is a necessary condition for enhancing the conductivity of polymer thin films. RF technique of plasma polymerisation is an excellent tool to induce conjugation and this modifies the electrical properties too. Both oxidative and reductive doping can be employed to modify the electrical properties of the polymer thin films for various applications. This is where organic thin films based on polymers scored over inorganic thin films, where in large area devices can be fabricated with organic semiconductors which is difficult to achieve by inorganic materials. For such applications, a variety of polymers have been synthesized such as polyaniline, polythiophene, polypyrrole etc. There are newer polymers added to this family every now and then. There are many virgin areas where plasma polymers are yet to make a foray namely low-k dielectrics or as potential nonlinear optical materials such as optical limiters. There are also many materials which are not been prepared by the method of plasma polymerisation. Some of the materials which are not been dealt with are phenyl hydrazine and tea tree oil. The advantage of employing organic extracts like tea tree oil monomers as precursors for making plasma polymers is that there can be value addition to the already existing uses and possibility exists in converting them to electronic grade materials, especially semiconductors and optically active materials for photonic applications. One of the major motivations of this study is to synthesize plasma polymer thin films based on aniline, phenyl hydrazine, pyrrole, tea tree oil and eucalyptus oil by employing both rf and ac plasma polymerisation techniques. This will be carried out with the objective of growing thin films on various substrates such as glass, quartz and indium tin oxide (ITO) coated glass. There are various properties namely structural, electrical, dielectric permittivity, nonlinear optical properties which are to be evaluated to establish the relationship with the structure and the other properties. Special emphasis will be laid in evaluating the optical parameters like refractive index (n), extinction coefficient (k), the real and imaginary components of dielectric constant and the optical transition energies of the polymer thin films from the spectroscopic ellipsometric studies. Apart from evaluating these physical constants, it is also possible to predict whether a material exhibit nonlinear optical properties by ellipsometric investigations. So further studies using open aperture z-scan technique in order to evaluate the nonlinear optical properties of a few selected samples which are potential nonlinear optical materials is another objective of the present study. It will be another endeavour to offer an appropriate explanation for the nonlinear optical properties displayed by these films. Doping of plasma polymers is found to modify both the electrical conductivity and optical properties. Iodine is found to modify the properties of the polymer thin films. However insitu iodine doping is tricky and the film often looses its stability because of the escape of iodine. An appropriate insitu technique of doping will be developed to dope iodine in to the plasma polymerized thin films. Doping of polymer thin films with iodine results in improved and modified optical and electrical properties. However it requires tools like FTIR and UV-Vis-NIR spectroscopy to elucidate the structural and optical modifications imparted to the polymer films. This will be attempted here to establish the role of iodine in the modification of the properties exhibited by the films

Magnetic field-induced cluster formation and variation of magneto-optical signals in zinc-substituted ferrofluids

Fine magnetic particles (size≅100 Å) belonging to the series ZnxFe1−xFe2O4 were synthesized by cold co-precipitation methods and their structural properties were evaluated using X-ray diffraction. Magnetization studies have been carried out using vibrating sample magnetometry (VSM) showing near-zero loss loop characteristics. Ferrofluids were then prepared employing these fine magnetic powders using oleic acid as surfactant and kerosene as carrier liquid by modifying the usually reported synthesis technique in order to induce anisotropy and enhance the magneto-optical signals. Liquid thin films of these fluids were prepared and field-induced laser transmission through these films was studied. The transmitted light intensity decreases at the centre with applied magnetic field in a linear fashion when subjected to low magnetic fields and saturate at higher fields. This is in accordance with the saturation in cluster formation. The pattern exhibited by these films in the presence of different magnetic fields was observed with the help of a CCD camera and was recorded photographically.

Electron energy loss spectroscopy assessment of cationic migration in La2/3Ca1/3MnO3 thin films

Màster en Nanociència i Nanotecnologia curs 2006-2007. Directors: Francesca Peiró i Martínez and Jordi Arbiol i Cobos

Investigations on the structural, optical and Magnetic properties of nanostructured cerium oxide in pure and doped forms and its polymer nanocomposiets

This thesis Entitled INVESTIGATIONS ON THE STRUCTURAL, OPTICAL AND MAGNETIC PROPERTIES OF NANOSTRUCTURED CERIUM OXIDE IN PURE AND DOPED FORMS AND ITS POLYMER NANOCOMPOSITES.Synthesis and processing of nanomatelials and nanostmctures are the essential aspects of nanotechnology. Studies on new physical properties and applications of nanomaterials and nanostructures are possible only when nanostructured materials are made available with desired size, morphology,crystal structure and chemical composition.Recently, several methods have been developed to prepare pure and doped CeO2 powder, including wet chemical synthesis, thermal hydrolysis, flux method, hydrothermal synthesis, gas condensation method, microwave technique etc. In all these, some special reaction conditions, such as high temperature, high pressure, capping agents, expensive or toxic solvents etc. have been involved.Another hi gh-li ght of the present work is room temperature ferromagnetism in cerium oxdie thin films deposited by spray pyrolysis technique.The observation of self trapped exciton mediated PL in ceria nanocrystals is another important outcome of the present study. STE mediated mechanism has been proposed for CeO2 nanocrystals based on the dependence of PL intensity on the annealing temperature. It would be interesting to extent these investigations to the doped forms of cerium oxide and cerium oxide thin films to get deeper Insight into STE mechanism.Due to time constraints detailed investigations could not be canied out on the preparation and properties of free standing films of polymer/ceria nanocomposites. It has been observed that good quality free standing films of PVDF/ceria, PS/C61‘l8, PMMA/ceria can be obtained using solution casting technique. These polymer nanocomposite films show high dielectric constant around 20 and offer prospects of applications as gate electrodes in metal-oxide semiconductor devices.

Coverage effects on the magnetism of Fe/MgO(001) ultrathin films

Different aspects of the structure-magnetism and morphology-magnetism correlation in the ultrathin limit are studied in epitaxial Fe films grown on MgO(001). In the initial stages of growth the presence of substrate steps, intrinsically higher than an Fe atomic layer, prevent the connection between Fe islands and hence the formation of large volume magnetic regions. This is proposed as an explanation to the superparamagnetic nature of ultrathin Fe films grown on MgO in addition to the usually considered islanded, or Vollmer-Weber, growth. Using this model, we explain the observed transition from superparamagnetism to ferromagnetism for Fe coverages above 3 monolayers (ML). However, even though ferromagnetism and magnetocrystalline anisotropy are observed for 4 ML, complete coverage of the MgO substrate by the Fe ultrathin films only occurs around 6 ML as determined by polar Kerr spectra and simulations that consider different coverage situations. In annealed 3.5 ML Fe films, shape or configurational anisotropy dominates the intrinsic magnetocrystalline anisotropy, due to an annealing induced continuous to islanded morphological transition. A small interface anisotropy in thicker films is observed, probably due to dislocations observed at the Fe¿MgO(001) interface.

Evidence of extended orientational order in amorphous Fe/Sm thin films

Amorphous thin films of Fe/Sm, prepared by evaporation methods, have been magnetically characterized and the results were interpreted in terms of the random magnets theory. The samples behave as 2D and 3D random magnets depending on the total thickness of the film. From our data the existence of orientational order, which greatly influences the magnetic behavior of the films, is also clear.

Magnetic field effect on quantum corrections to the low-temperature conductivity in mettalic perovskite oxides

The transport and magnetotransport properties of the metallic and ferromagnetic SrRuO3 (SRO) and the metallic and paramagnetic LaNiO3 (LNO) epitaxial thin films have been investigated in fields up to 55 T at temperatures down to 1.8 K . At low temperatures both samples display a well-defined resistivity minimum. We argue that this behavior is due to the increasing relevance of quantum corrections to the conductivity (QCC) as temperature is lowered; this effect being particularly relevant in these oxides due to their short mean free path. However, it is not straightforward to discriminate between contributions of weak localization and renormalization of electron-electron interactions to the QCC through temperature dependence alone. We have taken advantage of the distinct effect of a magnetic field on both mechanisms to demonstrate that in ferromagnetic SRO the weak-localization contribution is suppressed by the large internal field leaving only renormalized electron-electron interactions, whereas in the nonmagnetic LNO thin films the weak-localization term is relevant.

Ni filled flexible multi-walled carbon nanotube–polystyrene composite films as efficient microwave absorbers

In this letter, we report flexible, non corrosive, and light weight nickel nanoparticle@multi-walled carbon nanotube–polystyrene (Ni@MWCNT/PS) composite films as microwave absorbing material in the frequency range of S band (2-4 GHz). Dielectric permittivity and magnetic permeability of composites having 0.5 and 1.5 wt. % filler amount were measured using the cavity perturbation technique. Reflection loss maxima of 33 dB (at 2.7 GHz) and 24 dB (at 2.7 GHz) were achieved for 0.5 and 1.5 wt. % Ni@MWCNT/PS composite films of 6 and 4 mm thickness, respectively, suggesting that low concentrations of filler provide significant electromagnetic interference shielding