Studies on Giant and Colossal Magnetoresistance of Alloy and Ceramic Prepared by RF Magnetron Sputtering and Pulsed Laser Ablation Techniques

Magnetic thin films based on the giant magnetoresistance (GMR) and colossal magnetoresistance (CMR) effects are currently being used as head sensor in the magnetic data storage technology. With the technological revolution in the magnetic recording world of last decades, a need of better and more sensitive magnetoresistance material arises for head sensing. In the first part of this work, a series of Ag-Fe-Co granular films with different composition and thickness had been fabricated onto microscope glass slides using RF magnetron sputtering system. The crystalline analysis show that the as-deposited films consist of and silver texture. Negative GMR values have been obtained and no tendency to saturate at any temperature has been observed. The experimental results show that the GMR value is governed by the composition, microstructure, thickness and temperature. Under an optimum condition, formation of the right shape and size of magnetic cluster in the matrix will cause rapid increase of the GMR value

Giant Magnetoresistance of Silver Nickel Iron Grandular Magnetic Thin Films Prepared by RF Magnetron Sputtering System

The discovery of giant magnetoresistance (GMR) in multilayer system and subsequently in granular films has stimulated world wide research activities, due to both its fundamental significance and its potential application to magnetic sensors and data storage. Hence, this work is carried out to investigate this phenomenon. The first part of the work is to find out the suitable parameter and condition for producing good quality films. Granular magnetic thin films of Ag- Ni-Fe have been prepared at different deposition rates and compositions using RF Magnetron Sputtering system. Subsequently, the surfaces of the thin films were examined using the scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis, also in the SEM, was used to determine the composition of the films. The crystalline state of the films was determined by X-ray diffraction using CuKa radiation in a 29 powder diffractometer and the resistances of the films were measured using a four-point probe method to calculate the GMR effect. Lastly, the data obtained were analysed to investigate and understand the electrical transport mechanism in thin films. The result shows that the GMR effect is thickness, structure and composition dependent. The highest GMR value was obtained for the samples deposited for 60 minutes with 25% of magnetic entities embedded in the non-magnetic matrix. The microstructure analysis shows that the highest GMR value was obtained if the formation of fcc Ag texture is dominant and small grain size was formed in the film. In conclusion, a good granular thin film with high GMR value of 3.73% at room temperature has been developed and this result meets the requirement in the magnetic sensors and data storage industry

Electrical, magnetoresistance and magnetotransport properties of Nd1−xSrxMnO3

The effects of Sr substitution on the electrical, magnetoresistance and magnetotransport properties of Nd1−xSrxMnO3 were studied. Nd1−xSrxMnO3 samples were prepared using the solid-state reaction method with x=0.12, 0.152, 0.22, 0.252 and 0.32. All samples showed an orthorhombic structure, and no impurities were detected when the samples were examined using the X-ray diffraction method. The grain size was between 10 μm and 16 μm for all samples. The sample with x=0.32 showed the smallest grain size and the lowest To value, where To reflects the MnOMn bond angle. As the Sr concentration increased, the grains grew into more pentagonal and hexagonal shapes, and the insulator–metal transition temperature, Tim, also increased from 131 K to 180 K. The exceptions were the samples with x=0.152 and 0.252, where charge ordering was found at 120 K. The samples with the most pentagonal and hexagonal shaped grains (x=0.32) had the highest Tim. The magnetoresistance (MR) values were found to increase with increasing magnetic field. The sample with x=0.32 showed the highest MR value (31.5%), the highest Tim, the smallest grain size (∼10 μm) and the least bending of the MnOMn bonding angle

Influence of Pt on structural and morphologycal properties of La2O3/SnO2 thick film

In this study, the effect of Lanthanum oxide doped tin oxide (La2O3/SnO2) surface modification by Pt synthesized in the structural properties of SnO2 was presented. Samples (2wt.% La2O3, SnO2, 2 wt.% La2O3, SnO2, 1 wt.% Pt)were prepared using the ball milling method with m-xylene medium and they were calcined under700 °C. The thick film resistive paste based on SnO2 was fabricated on alumina substrate using screen printing technique. In order to prepare the printable thick film paste, the calcined resistive powders were mixed with organic vehicle and glass frit on alumina substrate with good rheology. Afterward, thermal treatment (drying and firing) was applied to dry the solvant from the printed paste and bonding the resistive paste on alumina substrate. The particle size and crystallinity of samples were characterized using X-Ray Powder Diffraction (XRD) spectroscopy and Transmission Electron Microscopy (TEM). TEM results illustrate that the obtained material are nanoparticles in spherical shape and the size of particles decreases with addition of Pt. The XRD pattern results show that the prepared samples are the nanopowders with almost spherical crystalline structure. The thick film surface morphology was investigated by Field Emission Scanning Electron microscopy (FE-SEM) before and after Pt doping and Energy Dispersive X-Ray spectroscopy (EDX) was used to determine the elemental composition.The results proved the nanometric size of all particles and it illustrated that the particle size of materials decreased with the addition of Pt on La2O3/SnO2

Effect of Co substitution on magnetic and magnetoresistance effect in La0.67(Ba1-xCox)0.33mno3 system

A series of polycrystalline perovskite manganite of La0.67(Ba1-xCox)0.33MnO3 (x=0.00, 0.30 and 0.50) were prepared by conventional solid-state route. XRD spectrum indicates that single phase rhombohedral perovskite structure had been obtained for x=0.00 sample. When Co is introduced in the Ba site, its structure is distorted from rhombohedral to pseudo-cubic. The SEM images show that the average grain sizes were found to be in 3-8µm (x=0.30) and 2-10µm (x=0.50) with less pore between the grain. For x=0.00, the sample is found in melted condition where no significant clear grain boundary can be found. Pure sample had TC of 343K. However, substitution of Co at Ba site brings down the Curie temperature, TC below 293K. Pure (x=0.0) sample shows Low Field Magnetoresistance (LFMR) effect and the effect weakens when Co is introduced. The highest low-field MR value is -13.0% for sample with x=0.00 in 0.1Tesla applied external magnetic field at 90K and the highest MR value of -22.5% is given by x=0.30 sample at 1Tesla applied magnetic field at 90K. Hence, these indicated that Co will not enhance the extrinsic MR which is due to the grain boundary effect and tend to destroy the LFMR effect

Sintering temperature study on structure, magnetic properties and magnetoresistance of Pr0.67Ba0.33MnO3

Polycrystalline perovskite manganite of Pr0.67Ba0.33MnO3 (PBMO) bulk ceramic samples were prepared by conventional solid‐state reaction method. The structures, typical magnetic properties and magnetoresistance were studied. At lower sintering temperature (900 °C to 1100 °C), formation of PBMO phase accompany by secondary phases of BaMnO3 and Pr6O11 were observed. However, at 1200 °C, pure single phase of PBMO was obtained. PBMO compounds become denser upon the increase in sintering temperature. A reduction of secondary phases as sintering temperature increased lead to the enhancement of magnetization value. The highest room temperature %MR of 17.1% was found in sample sintered at 1200 °C in 10 kG external magnetic field. In summary, higher sintering temperature reduced multiphase formation and enhanced the magnetic and magnetoresistance properties

Magnetoresistive and magnetic properties of La0.67A0.33MnO3 (A= Ba, Ca, and Sr) prepared by co-precipitation method.

We have prepared perovskite structured La0.67A0.33MnO3 manganite (A = Ba, Ca and Sr) using co-precipitation method. The samples were characterized using x-ray diffraction (XRD) and scanning electron microscope (SEM) to identify the structure and microstructure. The magnetic and magnetoresistance properties were measured by vibrations sample magnetometer (VSM) and four point probe methods. From the XRD spectrum, samples are in single phase pervoskite structure where LBMO and LCMO showed orthorhombic whereas LSMO has rhombohedral phase. LSMO has average grain size range of 0.5μm -2.5μm. However, for LBMO and LCMO, the grain boundaries are not well define and connected. The difference in the microstructure image might be due to the different activation energy and variance A-site cation that differs in grain growth. The Curie temperature of LBMO and LSMO are 343K and 371K, respectively. LCMO system gives the highest CMR value (-10.1% at 1 tesla) at room temperature. A significantly low field magnetoresistance effect (LFMR) which is -13.9% (at 0.1T, 90K) has been observed in LBMO and this LFMR effect is believed to be due to the disorder layers at the grain boundaries in the samples

Effect of calcination temperature on electrical properties of Nd0.7Ba0.3MnO3

In this work, Nd0.7Ba0.3MnO3 was synthesized via cryo-milling method to investigate the effect of calcination temperature on the structure, microstructure, magnetic and electrical properties. XRD analysis revealed all samples can be indexed to orthorhombic structure systems with Imma space group accompany with some minor phases of Mn2O4 and BaMnO3. FESEM analysis confirmed that a slight increase in the grain size from 117.4 nm (600°C), 119.5 nm (700°C), 121.0 nm (800°C), 123.1 nm (900°C) to 138.4 nm (1000°C) was observed when different calcination temperature was applied. Four Point Probe measurements showed that all samples are in paramagnetic insulating region and TMIT is lower than 20K. Resistivity increase when grain size reduces due to increase of effective grain boundary that weakens the electron hopping process via double exchange mechanism. Beside, a drastic increase of resistivity also observed due to present of minor secondary phase (BaMnO3) in sample C9

Effects of rare earth nanoparticles (M = Sm2O3, Ho2O3, Nd2O3) addition on the microstructure and superconducting transition of Bi1.6Pb0.4Sr2Ca2Cu3O10+δ ceramics

The effect of rare earth nanoparticles, M=Sm2O3, Nd2O3 and Ho2O3 added to (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(M)x, where x = 0.00 - 0.05, superconductor were studied by X-ray diffraction technique (XRD), resistivity (R), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX). The volume fraction of high-Tc phase, Bi-2223, decreased from 84% for pure sample to 48, 30 and 23% at x = 0.05 for Sm2O3, Ho2O3 and Nd2O3 additions, respectively. The critical temperature Tc(R=0) that is 102 K for the pure sample decreased to 78, 73 and 69 K at x = 0.05 for samples with Sm2O3, Nd2O3 and Ho2O3 nanoparticles additions, respectively. The additions of rare earth nanoparticles decreased the grain size and increased the random orientation of the grains. The results showed that the phases’ formations, variations of lattice parameters and electrical properties are sensitive to the size of nanoparticles and magnetic properties of its ions

Effect of sintering temperature on the superconducting properties of MgB2 superconductor co-added with a high concentration of Si and C

In this study, as much as 10 and 15 wt.% nanosized silicon and carbon (Si+C) were reacted with (Mg+2B) at 650°C and 850°C, respectively, for 1 hour. The phase formation, surface morphology and superconducting properties of these samples were evaluated. The relative peak intensity as calculated from the XRD patterns indicates the formation of large Mg2Si volume fraction at low sintering temperature. MgB4 phase was detected in the samples sintered at high temperature as a result of Mg deficiency. The C substitution level as estimated from the lattice parameters, was shown to increase in the samples reacted with a higher amount of (Si+C) at high temperature. Scanning electron micrograph showed that (Si+C) co-addition had refined the grain size and improved the grain coupling of MgB2. The superconducting transition temperature was found to decrease with increasing addition level. The superconducting transition width was also broadened because of a large volume fraction of secondary phases. The improved field dependent critical current density at both 5 K and 20 K is accounted to enhanced scattering by C substitution and grain boundary pinning