Laser-driven synthesis and magnetic properties of iron nanoparticles (original) (raw)
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Oxidation states and magnetism of Fe nanoparticles prepared by a laser evaporation technique
Journal of Applied Physics, 1996
Nanoparticles of iron and iron oxide have been prepared in a thermal diffusion cloud chamber using pulsed laser evaporation. SEM/TEM studies of these particles reveal a size distribution with a mean diameter of about 60 Å. This is consistent with the mean particle size estimated from the magnetic data. The oxidation levels of these nanoparticles prepared at different partial oxygen pressures were investigated using FTIR. All the samples are found to exhibit superparamagnetism with blocking temperatures ranging from 50 K to above room temperature. Magnetic anisotropy constants are calculated from the frequency dependence of the blocking temperatures are found to be one quarter of magnitude higher than is known for the bulk.
MAGNETIC PROPERTIES OF IRON OXIDE NANOPARTICLES OBTAINED BY LASER EVAPORATION
The paper concentrates on a synthesis of spherical magnetic particles obtained by laser evaporation under various process conditions. Depending on the process conditions, which include the pressure in a process chamber, laser pulse duration, mean laser power, and the type of power gas, the stoichiometry of the material ranges from Fe 2.70 O 4 to Fe 2.84 O 4 , while the average diameter of nanoparticles ranges between 10–23 nm. The nanoparticles have an inverse spinel structure. In terms of the magnetic properties, the samples are a superparamagnetic ensemble. The spherical shape of the majority of nanoparticles as well as the existence of merely one magnetic phase are verified by the characteristics of microwave absorption. A relatively high saturation magnetization and a narrow size distribution of small nanoparticles obtained at 700 mmHg working pressure, 100 ms pulse duration, and 200 W laser power allow the authors to consider these conditions to be the most optimum for the nanopowder synthesis and recommend them for biological applications.
Magnetic properties of nanometric Fe-based particles obtained by laser-driven pyrolysis
Journal of Physics and Chemistry of Solids, 2007
Fe-based nanoparticles were prepared by laser pyrolysis method using a cross-flow reactor in which the CO 2 laser radiation orthogonally crosses with the stream of Fe(CO) 5 , C 2 H 2 , and C 2 H 4 gases. The as-synthesised powder was characterised by HRTEM, XRD, Mo¨ssbauer spectroscopy, and low-and high-temperature magnetic measurements. The as-synthesised powder consisted of a-Fe and Fe 3 O 4 /g-Fe 2 O 3 nanoparticles embedded in a pyrolytic carbon matrix. The XRD pattern of the sample exhibited broad peaks. The crystallite size d XRD was estimated using the Scherrer formula and it was 1.8 nm for a-Fe and 1.6 nm for pyrolytic carbon. The assynthesised nanopowder was superparamagnetic. The blocking temperature was determined from the maximum of the ZFC curve and it was 32 K. After the sample had been cooled down to 4 K, the Mo¨ssbauer-Lamb factor f strongly increased. r
Iron ultrafine nanoparticles prepared by aerosol laser pyrolysis
Materials Letters, 2003
a-Fe nanoparticles have been prepared by a continuous process based on the CO 2 laser-induced pyrolysis of an iron pentacarbonyl aerosol. Uniform spherical nanoparticles of diameters between 13 and 24 nm consisting of an iron core and an oxide layer were obtained by this technique. It has been found that the mean particle size and the proportion of iron oxide vary with the laser power. Structural characteristics of the samples were determined by TEM and X-ray diffraction (XRD). Size distributions, determined both from TEM measurements and from X-ray diffraction by fitting the Fe(110) diffraction peak profile, are compared and discussed. Finally, the magnetic characterisation of the iron powders was carried out by attending to the hysteresis loop characteristics at room temperature.
The Influence of Magnetic Field on Synthesis of Iron Nanoparticles
Journal of nanoscience and nanotechnology applications, 2017
One of today's tasks is the development of new strategies for the synthesis of ferromagnetic, superparamagnetic nanoparticles immobilized in a polymer or carbon nanostructured matrix, and studying of the possibility of influencing their structure and magnetic properties. When the critical parameter that determines certain phenomena (the size of magnetic domains, the characteristic length of exchange interactions, the length of magnetostatic interactions, etc.) becomes comparable to the particle size, nanoscale magnetic materials exhibit sharp (dramatic) variability of magnetic properties. Therefore, there is a need to develop new methods of synthesis, protection and certification of such nanosystems to synthesize promising magnetic materials using technologically controlled processes. The encapsulation of metal nanoparticles into carbon chemically inert graphite like shells allows the synthesis of new generation materials to begin. Magnetic nanoparticles occupy an important place among these materials and such nanoparticles, which can be technologically important magnetic materials, will be investigated in this paper. The formation of nanocomposites, the production of nanoparticles of the same size and, accordingly, with reproducible properties, is one of the main technological tasks of this research. Methods of obtaining, which allow us to precisely control the size of particles are continuously improved. Magnetic nanostructured materials with unique electrical, mechanical, catalytic, optical and, moreover, specific magnetic properties, make it possible to constantly expand their fields of application in computer science, catalysis, for sensors production, in medicine and in biology. The correlation between nanostructure and magnetic properties allows us to offer different types of magnetic nanostructures: (1) systems with isolated particles, whose unique magnetic properties derive from decreasing sizes of components; (2) ultrafine particles with a cortical structure; (3) materials in which magnetic interaction is the dominant property; (4) nanocomposites, which consist of magnetic particles encapsulated in a chemically inert matrix. The magnetic properties in this case are determined by the ratio of volume fractions of magnetic particles and the matrix. In this work, we studied the effect of an external magnetic field on the formation and phase composition of iron particles synthesized in an arc discharge in a liquid phase. These products can be technologically important magnetic materials.
Reproducibility of the Synthesis of Iron Oxide Nanoparticles Produced by Laser Pyrolysis
2010
During the development of the BONSAI Project, the need for high quantities of iron oxide nanoparticles with some specific characteristics intensified the problem of the reproducibility in the nanoparticle production. Given the fact that the reaction yield for the production of the smallest and more homogeneous nanoparticles (BONFEX4) was very low (in the range of 1g/day), the process had to be repeated several times. These repetitions involved the use of three different CO 2 lasers (two of monomodal gaussian beams TEMoo mode with spot sizes of 4 and 3.5 mm and one multimodal of 4 mm spot size). Keeping constant the rest of the experiment parameters (including the laser density) we obtained similar powders in nature as revealed by X-ray diffraction, and similar particle size distributions, but with different magnetic properties. When the same laser was used the reproducibility of the magnetic properties increased significantly.
Impact of thermal oxidation on chemical composition and magnetic properties of iron nanoparticles
Journal of Magnetism and Magnetic Materials, 2018
The main objective of this work is to study the influence of thermal oxidation on the chemical composition and magnetic properties of iron nanoparticles which were manufactured in a simple chemical reduction of Fe 3+ ions coming from iron salt with sodium borohydride. The annealing processing was performed in an argon atmosphere containing the traces of oxygen to avoid spontaneous oxidation of iron at temperatures ranging from 200 °C to 800 °C. The chemical composition and magnetic properties of as-prepared and thermally-treated nanoparticles were determined by means of X-ray diffractometry, Raman spectroscopy, Mössbauer spectroscopy and vibrating sample magnetometry. Due to the magnetic interactions, the investigated iron nanoparticles tended to create the dense aggregates which were difficult to split even at low temperatures. This causes that there was no empty space between them, which led to their partial sintering at elevated temperatures. These features hindered their precise morphological observations using the electron microscopy techniques. The obtained results show that the annealing process up to 800 °C resulted in a progressive change in the chemical composition of as-prepared iron nanoparticles which was associated with their oxidation. As a consequence, their magnetic properties also depended on the annealing temperature. For instance, considering the values of saturation magnetization, its highest value was recorded for the as-prepared nanoparticles at 1 T and it equals 149 emu/g, while the saturation point for nanoparticles treated at 600 °C and higher temperatures was not reached even at the magnetic field of about 5 T. Moreover, a significant enhancement of coercivity was observed for the iron nanoparticles annealed over 600 °C.
Synthesis of Highly Magnetized Iron Nanoparticles by a Solventless Thermal Decomposition Method
The Journal of Physical Chemistry C, 2007
The R-Fe nanoparticle was successfully synthesized by a solventless thermal decomposition method. The metal 2+-oleate 2 complex prepared with metal salts and surfactant in aqueous solution was transformed to metal oxide. The metal oxide nanoparticle synthesized from the metal 2+-oleate 2 complex was mixed with salt powder as a separating media. The metal oxide mixture was reduced to R-Fe nanoparticles by Ar + 4% H 2 mixture gas, and then it was annealed under a high-vacuum system of 1.8 × 10-5 Torr at 700°C. The NaCl powder that was used instead of a surfactant plays an important role to keep the size and shape of the nanoparticles. The magnetization value of the prepared R-Fe nanoparticles is 213 emu/g, and the mean particle size of the R-Fe nanoparticles is 35 nm.
J. Magn. Magn. Mater. 316(2) pp. e1-e4 (2007)
Iron oxide nanoparticles were synthesized by the thermal decomposition of Fe(acac) 3 and Fe(CO) 5 . Three different homogeneous procedures were used for the controlled synthesis of Fe 3 O 4 , γ-Fe 2 O 3 and Fe 3 O 4 /γ-Fe 2 O 3 mixture nanocrystals. A combination of characterization techniques was used in order to distinguish these oxides. The controllable size, the narrow distribution and the rhombic self assembly of the nanoparticles were revealed by the HRTEM images and the XRD results. For the quantitative analysis of the samples manganometry was used. Preliminary magnetic measurements indicated the size and composition dependence of saturation magnetization, a superparamagnetic behavior of the samples and some ferromagnetic features.
Nanotechnology, 2013
A novel way has been proposed to follow the formation of nanocrystalline magnetite. Iron oxide nanoparticles were synthesized by the thermal decomposition of Fe(acac) 3 in the presence of oleic acid and oleylamine surfactants at high temperature. The species produced during the synthetic process are characterized through their effects on the proton nuclear magnetic relaxation of the reaction medium and their sizes. As shown by transmission electron microscopy, photon correlation spectroscopy and x-ray diffraction, the diameter of nano-objects increases when the time synthesis is longer. Magnetic properties evaluated by nuclear magnetic resonance (NMRD profiles, T 1 and T 2 measurements) were correlated with the size parameters.