Magnetic-property enhancement of sized controlled cobalt-gold core-shell nanocrystals

Cobalt nanoparticles and cobalt-gold core-shell nanoparticles were synthesized via reverse-micelle microemulsion method with emphasis on size control. Cobalt nanoparticles become easily oxidized therefore coating a gold shell on cobalt nanoparticles was necessary and can effectively reduce the oxidation of Co while maintaining most of its magnetic properties. Controlling the size of nanoparticles was performed by adjusting the water to surfactant ratio of reverse micelle solution during synthesis. X-ray diffraction data was used to calculate the crystallinity percentage and percentage of phases presented in Co-Au core-shell nanoparticles. The results from transmission electron microscopy, and field emission electron microscopy combined to energy dispersive x-ray spectroscopy provide direct evidence for shell growth. The average coating layer (shell thickness) in all cases observed to be 4-5 nm. Magnetic properties of samples were investigated using a vibrating sample magnetometer before and after annealing. Magnetic properties enhanced after annealing in all cases. An increase in saturation magnetization after annealing was due to increase in cystallinity percentage. A simple method was applied to measure a totally intrinsic blocking temperature in zero field cooled-warmed (ZFC-W) curves without employing an external magnetic field. The B-field dependence temperature data of Co-Au nanoparticles before and after annealing showed an intrinsic blocking temperature of 45 and 40 K respectively

Phase transformation, structure and magnetic properties of Nd9.4Pr0.6FebalTixCxCo6Ga0.5B6 ribbons prepared by melt-spinning method

The effect of Carbon and Titanium additions on the phase constitution, microstructures and the magnetic properties of Nd-Fe-B isotropic nanocomposite processed from Nd9.4Pr0.6FebalCo6B6Ga0.5TixCx (x=0, 3, 6) ribbons has been investigated. As-spun ribbons were examined by using X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). Optimally quenched and annealed Nd9.4Pr0.6FebalCo6B6Ga0.5TixCx (x=0, 3, 6) ribbons at 750 °C for 10 minutes, which was composed of Nd2Fe14B grains separated by α-Fe grain boundary phase, shows addition of Ti suppresses formation of primary Fe and promotes formation of ferromagnetic iron-borides. Carbon addition is effective for grain refinement and suppression of unfavourable formation of TiB2; resulting in improvement of magnetic properties. The results show that Titanuim and Carbon additions enhance the glass forming ability and increase the crystallization temperature. XRD results of annealed ribbons indicate that Ti and C react to form TiC. The grain size was substantially refined by the addition of Ti due to the formation of Ti-enriched amorphous grain boundaries. The XRD and Atomic force microscope (AFM) technique results confirm that grains are in the size of less than 70 nm. Furthermore, addition of C enhanced the enrichment of Ti in the grain boundary phase, which led to the increase of the coercivity and the maximum energy product

High coercivity sized controlled cobalt–gold core–shell nano-crystals prepared by reverse microemulsion

Size-controlled cobalt–gold core–shell nanoparticles were synthesized via the reverse-micelle microemulsion method. In order to control the size of the nanoparticles, the nucleation and growth process were performed within a confined space by adjusting the water to surfactant ratio of reverse micelles solution during synthesis. The crystallinity percentage and percentage of phases presented in Co–Au core–shell nanoparticles were calculated using X-ray diffraction data. The results from transmission electron microscopy provide direct evidence for core–shell structure nanomaterials. Magnetic properties of the samples were investigated using a vibrating sample magnetometer. The as-prepared samples showed significant coercivity at room temperature. The intrinsic blocking temperature was experimentally deduced from zero-field-cooled warmed (ZFC-W) curves by a simple method without employing an external magnetic field. The B-field dependence temperature data of Co–Au nanoparticles exhibited an intrinsic blocking temperature at 45 K. Annealing these samples at 400 °C caused an increase in particle size, crystallinity percentage and further enhanced their magnetic properties

Recording-media-related morphology and magnetic properties of crystalline CoPt3 and CoPt3-Au core-shell nanoparticles synthesized via reverse microemulsion

A comparative experimental study of the magnetic properties of CoPt3 and CoPt3/Au nanoparticles as well as a detailed study of the structural properties of the samples by X-ray diffraction, Transmission electron microscopy, and vibrating sample magnetometer is presented in this work. In addition, the effect of particle size on the structure and magnetic properties of nanoparticles prepared by microemulsion is studied. The correlation between particle size, crystallinity, and magnetization was studied as well. CoPt nanoparticles have been studied intensively over the last decade because of their increased magnetic anisotropy in the ordered phase that can be interesting for high density magnetic recording. A significant high coercivity for as-prepared CoPt3 and CoPt3-Au nanoparticles was obtained at room temperature and enhanced after annealing. The focused aim of our study is to obtain high coercivity at room temperature that follows the Curie-Weiss law. This indicates an interacting system in which the nanoparticles behave like single domain ferromagnetic materials in the particle size range of 8 to 35 nm. In addition, the interaction increases by cooling the samples to low temperature around 15 K. Temperature dependence 1/M graph was obtained to investigate the behavior of nanoparticles at low temperature and shows the best fit with Curie-Weis mode

Growth and characterization of La5/8 Sr3/8 MnO3 thin films prepared by pulsed laser deposition on different substrates

Colossal magnetoresistance La5/8Sr3/8MnO3 (LSMO) thin films were directly grown on MgO(100), Si(100) wafer and glass substrates by pulsed laser deposition technique. The films were characterized using X-ray diffraction (XRD), field emission-scanning electron microscope and atomic force microscopy (AFM). The electrical and magnetic properties of the films are studied. From the XRD patterns, the films are found to be polycrystalline single-phases. The surface appears porous and cauliflower-like morphology for all LSMO films. From AFM images, the LSMO films deposited on glass substrate were presented smooth morphologies of the top surfaces as comparing with the films were deposited on Si(100) and MgO(100). The highest magnetoresistance (MR) value obtained was −17.21 % for LSMO/MgO film followed by −15.65 % for LSMO/Si and −14.60 % for LSMO/Cg films at 80 K in a 1T magnetic field. Phase transition temperature (TP) is 224 K for LSMO/MgO, 200 K for LSMO/Si and above room temperature for films deposited on glass substrates. The films exhibit ferromagnetic transition at a temperature (TC) around 363 K for LSMO/MgO, 307 K for LSMO/Si and 352 K for LSMO/Cg thin film. TC such as 363 and 352 K are the high TC that has ever been reported for LSMO films deposited on MgO substrate with high lattice mismatch parameter and glass substrates with amorphous nature

Enhancement of visible light photocatalytic activity of ZnS and CdS nanoparticles based on organic and inorganic coating

Coating of ZnS and CdS nanoparticles with organic and inorganic materials can extend their light absorption in the visible region and their stability against photo-corrosion. Such materials could emerge as excellent photocatalysts for the elimination of pollutants from aqueous media using solar energy. In this study, PVP (polyvinyl pyrrolidone)-capped ZnS and CdS nanoparticles, ZnS/CdS and CdS/ZnS core shell nanoparticles were synthesized by microwave irradiation method and characterized using different techniques. The XRD patterns exhibited cubic and hexagonal structures for coated ZnS and CdS nanoparticles, respectively. Morphological evaluation of TEM images showed that the nanoparticles are generally spherical in shape. The UV–visible spectra confirmed a shift in the band gap of coated nanoparticles to longer or shorter wavelengths due to size and potential-well effects. The photocatalytic activity of nanoparticles toward dye degradation under visible light was found to be improved after coating. PVP-capped ZnS and CdS exhibited an enhancement in the initial methylene blue degradation efficiency by a factor of about 1.3. ZnS nanoparticles coated by CdS displayed the initial efficiency 3.2 times higher than bare ZnS. The maximum dye removal was obtained in presence of CdS/ZnS core shells which is 1.4 times more efficient than bare CdS

Photocatalytic degradation of methylene blue under visible light using PVP-capped ZnS and CdS nanoparticles

Photocatalysis based on semiconductor quantum dots which utilize the solar energy can be used for the elimination of pollutants from aqueous media and applied for water purification. Degradation of dyes is a standard method to check the photocatalytic activity of any type of photocatalyst. In this paper polyvinyl pyrrolidone (PVP)-capped ZnS and CdS nanoparticles were prepared by a simple microwave irradiation method and studied in detail for their photocatalytic activity in visible range. The obtained nanoparticles were characterized by XRD, TEM, UV–Vis and EDX. The prepared PVP-capped ZnS and CdS nanoparticles have average sizes of ∼5.1 and 18.3 nm with cubic and hexagonal crystalline structures, respectively. PVP capped CdS nanoparticles exhibited a unique property of optical absorption in visible region with a wave length below than 460 nm followed by a clear long tail up to 700 nm and showed excellent activity toward degradation of dye under visible light illumination. The photocatalytic activity of PVP-capped CdS nanoparticles was found to be improved by mixing with appropriate amount of PVP-capped ZnS nanoprticles. From the study of variation in weight percentages of PVP-capped ZnS nanoparticles, the physical mixture with 20% of PVP-capped ZnS nanoparticles was found to be very efficient for degradation of methylene blue. In this case the degradation efficiency after 6 h illumination was about 81%

High curie temperature for La5/8Sr3/8MnO3 thin films prepared by pulsed laser deposition on glass substrates

The manganite LSMO films were successfully grown on glass substrates without any additional buffer layer by pulsed laser deposition. The films have been investigated by X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), electrical and magnetic measurements. From the XRD pattern the film is found to be polycrystalline single-phase’s character. The LSMO thin films growth on glass substrate, follows the island growth model with average grain size of 44.46nm. The metal-insulator transition (TMI) temperature was above room temperature and electrical conduction mechanism of LSMO films below phase transition temperature (TP) is due to the electron-electron (major) and electron-magnon scattering processes. The Curie temperature of LSMO films is around 352 K, which is one of the high TC in all LSMO films and as our knowledge, is the highest value that is reported in literature for low cost amorphous substrates such as glass. The low resistivity, high TMI and high TC makes these LSMO films very useful for room temperature magnetic devices

Growth and characterization of La0.7Na0.3MnO3 thin films prepared by pulsed laser deposition on different substrates

Perovskite manganite La0.7Na0.3MnO3 thin films were directly grown on MgO (1 0 0), Si (1 0 0) and glass substrates by pulsed laser deposition. From the XRD patterns, the films are found polycrystalline single-phases rhombohedral. The surface appears porous and cauliflower-like morphology for all LNMO films. LNMO films deposited on the glass substrate were presented smooth morphologies of the top surfaces as compared with other films. The highest magnetoresistance value obtained was −18.86% for LNMO/MgO films at 80 K in a 1 T magnetic field. Phase transition temperature is 221 K for LNMO/Cg, 214 K for LNMO/Si and 144 K for films deposited on MgO substrates. The films exhibit ferromagnetic transition at a temperature around 286 K for LNMO/MgO, 304 K for LNMO/Si and 292 K for LNMO/Cg thin film. The Curie temperature of LNMO films deposited on the glass substrate, 292 K is the highest value that is reported in literature for LNMO films deposited on low-cost amorphous substrates

Preparation and Characterization of PLGA Encapsulated Tamoxifen Citrate-Magnetite Nanoparticle Via Oil in Water Emulsion Evaporation Technique

Current research had successfully encapsulated magnetic nanoparticles (MNP) with selective estrogen receptor drug tamoxifen citrate (TAM) using Poly (d,l-lactice-co-glycolide acid) (PLGA 75:25) via oil in water emulsion technique. TAM is a good example of a drug that is difficult to dissolve. TAM is currently approved for the treatment of hormone-sensitive and early-stage breast cancer as an adjuvant endocrine therapy. The majority of the prescription medicine in today market is made up of poorly soluble, bioavailable, and quickly metabolized and eliminated drug which is a continuously challenges up to these days. Therefore, it is imperative to overcome this disadvantages by encapsulating TAM inside PLGA together with MNP for improved drug delivery. The MNP coated with oleic acid (OA) was synthesized using co-precipitation method and it is known as OAMNP. The fabricated nanohybrid is known as TAM-PLGA-OAMNP where the TAM was encapsulated together with OAMNP within PLGA. XRD results showed that OAMNP is Fe3O4. FTIR spectra revealed that the TAM was successfully encased into the PLGA structure. TAM-PLGA-OAMNP average size is about 131 ± 28 nm as shown in TEM results. The nanohybrid nanoparticles showed the absence of hysteresis loop indicative of superparamagnetic properties