Preparation of high crystalline nanoparticles of rare-earth based complex pervoskites and comparison of their structural and magnetic properties with bulk counterparts (original) (raw)
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Ultrasonics Sonochemistry, 2012
A novel technique was used for the synthesis of manganese oxide nanocrystal by applying an external magnetic field (EMF) on the precursor solution before sonication with ultrasonic bath. The results were compared in the presence and absence of EMF. Manganese acetate solution as precursor was circulated by a pump at constant speed (7 rpm, equal to flow rate of 51.5 mL/min) in an EMF with intensity of 0.38 T in two exposure times (t MF , 2 h and 24 h). Then, the magnetized solution was irradiated indirectly by ultrasonic bath in basic and neutral media. One experiment was designed for the effect of oxygen atmosphere in the case of magnetic treated solution in neutral medium. The as prepared samples were characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (HRTEM, TEM), energy-dispersive spectrum (EDS), and superconducting quantum interference device (SQUID) analysis. In neutral medium, the sonication of magnetized solution (t MF , 24 h) led mainly to a mixture of Mn 3 O 4 (hausmannite) and c-MnOOH (manganite) and sonication of unmagnetized solution led to a pure Mn 3 O 4. In point of particle size, the larger and smaller size of nanoparticles was obtained with and without magnetic treatment, respectively. In addition, the EMF was retarded the nucleation process, accelerated the growth of the crystal, and increased the amount of rod-like structure especially in oxygen atmosphere. In basic medium, a difference was observed on the composition of the products between magnetic treated and untreated solution. For these samples, the magnetic measurements as a function of temperature were exhibited a reduction in ferrimagnetic temperature to T c = 39 K, and 40 K with and without magnetic treatment, respectively. The ferrimagnetic temperature was reported for the bulk at T c = 43 K. A superparamagnetic behavior was observed at room temperature without any saturation magnetization and hysteresis in the measured field strength. The effect of EMF on the sample prepared in the basic medium was negligible but, in the case of neutral medium, the EMF affected the slope of the magnetization curves. The magnetization at room temperature was higher for the samples obtained in neutral medium without magnetic treatment. In addition, a horizontal shift loop was observed in neutral medium at low temperature.
A novel approach for the synthesis of superparamagnetic Mn3O4 nanocrystals by ultrasonic bath
Ultrasonics Sonochemistry, 2012
In this study, the synthesis of Mn 3 O 4 (husmannite) nanoparticles was carried out in two different alkali media under sonication by ultrasonic bath and conventional method. Manganese acetate was used as precursor, sodium hydroxide and hexamethylenetetramine (HMT) as basic reagents in this synthesis. An ultrasonic bath with low intensity was used for the preparation of nanomaterials. The as prepared samples were characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (HRTEM, TEM), energy-dispersive spectrum (EDS), and superconducting quantum interference device (SQUID) analysis. The XRD patterns exhibit the nanocrystals are in pure tetragonal phase. The chemical composition was obtained by EDS analysis and confirmed the presence of Mn and O in the sample. According to the TEM and HRTEM results, both nanorods and nanoparticles of Mn 3 O 4 were obtained in the presence of ultrasonic irradiation. The average size of nanoparticles was 10 nm, and the size of nanorods was 12 nm in diameter and 100-900 nm in length for the samples prepared in basic medium with sodium hydroxide. In the conventional method with the same basic medium, the nanorod was not observed and the nearly cubic nanoparticles was appeared with an average size of 2.5 nm. The selected area electron diffraction (SAED) patterns revealed that the nanocrystals are polycrystalline in nature. When HMT was used as a basic reagent in the presence of ultrasonic irradiation, it was led to a higher size of nanoparticles and nanorods than when sodium hydroxide was used as a basic reagent. The average size of nanoparticles was about 15 nm and its shape was nearly cubic. The diameter for nanorods was 50 nm and the length was about a few micrometers. The magnetic measurements were carried out on the sample prepared in sodium hydroxide under ultrasonic irradiation. These measurements as a function of temperature and field strength showed a reduction in ferrimagnetic temperature (T c = 40 K) as compared to those reported for the bulk (T c = 43 K). The superparamagnetic behavior was observed at room temperature with no saturation magnetization and hysteresis in the region of measured field strength.
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Physica B: Condensed Matter, 2006
Nanoparticles of the La 2=3 Sr 1=3 MnO 3 manganite were synthesized using the Pechini process and their structural properties were characterized by X-ray diffraction (XRD) and by transmission electron microscopy (TEM). The magnetization of compacted powders was measured for temperatures in the range 190pTp450 K. The estimated average diameter (D) of the particles continuously increased from 20 to 95 nm when the calcination temperature was varied from 873 to 1273 K. From the magnetic data we found that the room temperature saturation magnetization scaled with 1=D while the magnetic transition temperature follows a D 2 power-law suggesting that the correlation length x is mainly determined by the surface properties of the nanoparticles.
Synthesis of superparamagnetic Mn 3O 4 nanocrystallites by ultrasonic irradiation
Journal of Crystal Growth, 2005
Nanocrystalline Mn 3 O 4 has been synthesized by ultrasonic irradiation of Mn acetate solution in water. Analysis of its X-ray diffraction data shows formation of a phase-pure compound with an average particle size of about 15 nm. DC magnetization measurements as a function of temperature and field show a reduced ferrimagnetic transition temperature ðT c % 39 KÞ as compared to those reported for the bulk ðT c % 43 KÞ, and a subsequent observation of superparamagnetic behavior at 40 K. The observed magnetic properties are suggestive of formation of a single domain magnetically ordered Mn 3 O 4 nanoparticles below their ferrimagnetic transition temperature. r
Perovskite nanoparticles: Preparation by reactive milling and magnetic characteristics
Journal of Magnetism and Magnetic Materials, 2006
La 0.7 Sr 0.3 MnO 3 and La 0.7 Ca 0.3 MnO 3 nanoparticles were synthesized by reactive milling method. Grain size determined from XRD, TEM, and magnetization measurements show an average diameter p18 nm and decreasing with increasing milling time. DC and AC magnetic measurements evidenced an interacting superparamagnetism due to clustering of perovskite nanoferromagnets with spin dynamic time in range of 10 À9 -10 À10 s. r
Synthesis of magnetite nanoparticles by high energy ball milling
Applied Surface Science, 2013
We report on the preparation of magnetite nanoparticles, with size ranging from 12 nm to 20 nm, by high energy ball milling. The synthesis is made using stoichiometric amounts of distilled water and metallic iron powder. The milled powder samples were analyzed by Mossbauer spectroscopy (MS), Xray diffraction (XRD) and vibrating sample magnetometry (VSM). Our results indicate that the milling time is a key parameter of the synthesis. By increasing the milling time one achieves high purity magnetite samples. Also, the particle size decreases with the milling time. The sample milled during 10 h contained a fraction of 56 nm metallic Fe particles and 20 nm magnetite particles. By increasing the milling time to 96 h we have obtained a sample that is mainly composed of 12 nm magnetite particles. MS performed at room temperature showed a spectrum consisting of two sextets with hyperfine parameters related to iron ions occupying octahedral (A) and tetrahedral (B) sites. We have used a self-consistent method to investigate the impact of the dipolar interaction to drive the system to a magnetically blocked regime.
Journal of Solid State Chemistry, 2013
Syntheses of nanocrystalline perovskite phases of the general formula La 1−x Sr x MnO 3+δ were carried out employing sol-gel technique followed by thermal treatment at 700-900 1C under oxygen flow. The prepared samples exhibit a rhombohedral structure with space group R3c in the whole investigated range of composition 0.20≤x≤0.45. The studies were aimed at the chemical composition including oxygen stoichiometry and extrinsic properties, i.e. size of the particles, both influencing the resulting structural and magnetic properties. The oxygen stoichiometry was determined by chemical analysis revealing oxygen excess in most of the studied phases. The excess was particularly high for the samples with the smallest crystallites (12-28 nm) while comparative bulk materials showed moderate nonstoichiometry. These differences are tentatively attributed to the surface effects in view of the volume fraction occupied by the upper layer whose atomic composition does not comply with the ideal bulk stoichiometry.
Structural and magnetic properties of nanoparticles of La2/3Sr1/3MnO3
Nanoparticles of the La 2=3 Sr 1=3 MnO 3 manganite were synthesized using the Pechini process and their structural properties were characterized by X-ray diffraction (XRD) and by transmission electron microscopy (TEM). The magnetization of compacted powders was measured for temperatures in the range 190pTp450 K. The estimated average diameter (D) of the particles continuously increased from 20 to 95 nm when the calcination temperature was varied from 873 to 1273 K. From the magnetic data we found that the room temperature saturation magnetization scaled with 1=D while the magnetic transition temperature follows a D 2 power-law suggesting that the correlation length x is mainly determined by the surface properties of the nanoparticles. r
The Magnetic Properties of Mn0.3Mg0.2Zn0.5Fe2O4 and Mn0.3Mg0.2Co0.5Fe2O4: The Effect of Milling
Physics Procedia, 2015
Mn 0.3 Mg 0.2 Zn 0.5 Fe 2 O 4 and Mn 0.3 Mg 0.2 Co 0.5 Fe 2 O 4 nanoparticles with particle diameters of about 13 nm were synthesized by glycol-thermal method. The as-prepared specimens were then milled at different times up to 50 h and the single phase spinel structure confirmed by X-ray diffraction. The properties for the as-prepared and milled samples for the two systems were deduced and contrasted. Significant changes induced by milling in particle size, magnetization, coercive field and hyperfine parameters are reported. 57 Fe Mössbauer spectra at room temperature show ordered magnetic spin states in both Mn 0.3 Mg 0.2 Zn 0.5 Fe 2 O 4 and Mn 0.3 Mg 0.2 Co 0.5 Fe 2 O 4 by magnetization measurements.
Journal of Alloys and Compounds, 2009
In this work we report results on the influence of heavy rare earth ions substitution on microstructure and magnetism of nanocrystalline magnetite. A series of Fe 2.85 RE 0.15 O 4 (RE = Gd, Dy, Ho, Tm and Yb) samples have been prepared by high energy ball milling. Structure/microstructure investigations of two selected samples Fe 2.85 Gd 0.15 O 4 and Fe 2.85 Tm 0.15 O 4 , represent an extension of the previously published results on Fe 3 O 4 /␥-Fe 2 O 3 , Fe 2.85 Y 0.15 O 4 and Fe 2.55 In 0.45 O 4 [Z. Cvejic, S. Rakic, A. Kremenovic, B. Antic, C. Jovalekic, Ph. Colomban, Sol. State Sciences 8 908], while magnetic characterization has been done for all the samples.Crystallite/particle size and strain determined by X-ray diffractometry and Transmission electron microscopy (TEM) confirmed the nanostructured nature of the mechanosynthesized materials. X-ray powder diffraction was used to analyze anisotropic line broadening effects through the Rietveld method. The size anisotropy was found to be small while strain anisotropy was large, indicating nonuniform distribution of deffects in the presence of Gd and Tm in the crystal structure. Superparamagnetic (SPM) behavior at room temperature was observed for all samples studied. The Y-substituted Fe 3 O 4 had the largest H C and the lowest M S . We discuss the changes in magnetic properties in relation to their magnetic anisotropy and microstructure. High field irreversibility (H > 20 kOe) in ZFC/FC magnetization versus temperature indicates the existence of high magnetocrystalline and/or strain induced anisotropy.