Quantum Design Vibrating Sample Magnetometer Research Articles

Magnetic Nanoparticles Based on DABCO as Catalysts in the Knoevenagel Reaction and Synthesis of Isatin-β-thiosemicarbazones

This work describes the route to prepare a novel core-shell catalyst based on 1,4-diazabicyclo[2,2,2]octane (DABCO) supported magnetic nanoparticles (MNPs). The morphology and composition of the obtained catalysts were characterized by Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), quantum design vibrating sample magnetometer (VSM) and scanning electron microscopy (SEM). These nanomaterials presented high performance as a basic catalyst for Knoevenagel condensation between malononitrile and aldehydes, leading to products with excellent yields (84-99%) and short reaction times (5-60 min). Furthermore, it was also efficient in the condensation of isatins with 4-phenylthiosemicarbazide, resulting in isatin-β-thiosemicarbazones with high yields (81-94%) and short times (60-180 min). It is worth mentioning that the catalyst was recovered and reused in these two kinds of reactions after six cycles without significant yield loss.

Structure and magnetic properties Zn0.96Cu0.01Ni0.03O nanoparticles

Zn0.96Cu0.01Ni0.03O nanoparticles were prepared by sol-gel technique and annealed under wide temperature range (450, 500, 550, 600, 700, 800, and 900 0C). To figure out the possible structural phases X-ray diffraction technique (XRD) was used. The lattice parameters were calculated by Rietveld analysis and correlated by annealing temperatures. For the synthesized nanoparticles, the optimum annealing temperatures were achieved at 450, 500, and 550 °C and further annealing temperature increment gave rise to secondary NiO peaks. The Scanning Electron Microscope (SEM) images show random ball-shaped particle distribution. Energy dispersive X-ray spectroscopy (EDX) showed only the peaks belong to the composition. Magnetic measurements were performed using Quantum Design Vibrating Sample Magnetometer (QDVSM) tool for Zn0.96Cu0.01Ni0.03O nanosystems. From the DC magnetic field dependent magnetization curves, clear paramagnetic behavior was revealed for all Cu-Ni co-doped ZnO nanoparticles.

Effect of Annealing Temperature on Structure and Magnetic Properties of Zn0.94Mg0.01Mn0.05O Nanoparticles

Structural and magnetic characteristics of Zn0.94Mg0.01Mn0.05O (ZnMgMnO) nanoparticles synthesized by Sol-Gel preparation technique in a wide temperature range were reported. The influence of annealing temperature on the crystal structure of ZnMgMnO nanoparticles was figured out by X-ray diffraction technique (XRD). To optimize the annealing temperature and reveal the particle formation and size, Scanning Electron Microscope (SEM) imaging technique was performed. The required stoichiometry of the synthesized samples was obtained by an energy dispersive X-ray analysis technique (EDX). Quantum Design Vibrating Sample Magnetometer (QDVSM) tool was used for the magnetic characterizations of Zn0.94Mg0.01Mn0.05O composition. Magnetization measurements as a function of magnetic field (M-H) were performed in the magnetic field up to 10 kOe. Temperature dependence of magnetization measurements (M-T) was taken between 10 and 320 K temperature ranges.

The magnetic properties and microstructure of phosphated amorphous FeSiCr/silane soft magnetic composite

Abstract Herein, amorphous FeSiCr phosphating powders were prepared using two phosphating methods and were further formed into soft magnetic composites (SMCs). The effects of phosphating treatment on the morphology and composition of phosphate layers of amorphous FeSiCr particles and mechanisms of the phosphating process were investigated via scanning electron microscopy, X-ray diffraction (XRD), Fourier transform infrared spectra, and X-ray photoelectron spectroscopy. The magnetic properties of amorphous FeSiCr phosphating powders were determined via the Quantum Design vibrating sample magnetometer. The effects of heat and phosphating treatments on AC magnetic properties of SMCs were investigated using a B-H curve analyzer. Results showed that both phosphating treatments significantly increase the resistivity of amorphous FeSiCr and do not deteriorate its magnetic properties. However, owing to the thick phosphating layer of amorphous FeSiCr phosphate on the zinc phosphate solution, its compressibility deteriorated. The magnetic permeability of the SMC was very stable in the frequency range of 10–500 kHz. Following heat treatment at 500 °C in an argon atmosphere, the magnetic permeability of the SMC significantly increased, whereas the magnetic loss significantly reduced.

Effects of heat treatment on structure and magnetic properties of Fe/(NiZn)Fe2O4 soft magnetic composite powders prepared using a co-precipitation method

Fe powder was coated with precipitate via a co-precipitation method using chlorate as the raw material. Then, the coated powder was heat treated under different conditions. The effects of the heat treatment atmosphere and temperature on the morphology, phase formation, crystallinity, grain size and lattice constant of the coated layer of powders were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric–differential scanning calorimetry (TG–DSC). The magnetic properties of the composite powder were determined using a Quantum Design vibrating sample magnetometer (QD-VSM). The results show that a fine, uniform coating layer of particles formed on the surface of the Fe powder after co-precipitation. Through heat treatment, the coating generated spinel Ni–Zn ferrite. The coated layer of argon-treated powders had a more uniform and regular morphology, purer phase and better crystallinity than air-treated powders. The saturation magnetisation first increased and subsequently decreased as the heating temperature increased. Similarly, the coercivity first decreased and subsequently increased. The sample annealed in air at 300 °C had the highest saturation magnetisation (Ms = 186.3 emu/g) and the lowest coercivity (Hc = 23.6 Oe), whereas the sample annealed in argon at 450 °C had the greatest saturation magnetisation (Ms = 196.4 emu/g) and relatively lower coercivity (Hc = 17.5 Oe). The powders annealed in argon atmosphere had better Ms and lower Hc than those annealed in air, mainly because coated powders heated in air produce a large amount of non-magnetic Fe2O3.

PEG-Coated Superparamagnetic Dysprosium-Doped Fe3O4 Nanoparticles for Potential MRI Imaging

In recent years, superparamagnetic nanoparticles (NPs) have attracted considerable attention due to their high potential for biomedical applications. This study describes a facile preparation method of superparamagnetic polyethylene glycol (PEG)-coated dysprosium-doped Fe3O4 NPs for potential magnetic resonance imaging (MRI) applications. The structure, morphology, and magnetic properties of the dysprosium-doped Fe3O4 NPs were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and quantum design vibrating sample magnetometer (QD-VSM), respectively. The MRI imaging ability of the dysprosium-doped Fe3O4 NPs was assessed using a 1.5-T small animal MRI scanner. In addition, pilot studies were performed to examine the toxicity of the PEG-coated dysprosium-doped Fe3O4 NPs. The obtained results suggested that prepared NPs could be used for potential T2-weighted MRI imaging.

Fe-based soft magnetic composites coated with NiZn ferrite prepared by a co-precipitation method

Fe powder was coated with NiZn ferrite by a co-precipitation method using chlorate as the raw material. Soft magnetic composites were manufactured via compaction and heat treatment of the coated powder. The coated powder and heat treated powder were analysed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Raman spectroscopy. Their magnetic properties were determined using a Quantum Design-Vibrating Sample Magnetometer (QD-VSM). The composites were analysed with SEM and EDS. The permeability and magnetic loss of the composites were measured with a B-H curve analyzer. The results show that, using the co-precipitation method, the raw precipitate was successfully prepared and coated the pure Fe powder and turned into spinel NiZn ferrite treated at 600℃ for 1h. After heat treatment at 500℃ under air, the insulation coating layer of soft magnetic composite (SMC) was not destroyed and containing Fe, Ni, Zn and oxygen. The permeabilities of the SMC are stable at edge of the 2–200kHz frequency range and the total loss was lower.

Thickness Effect on Thermal Stability by Phase Transition of Single Crystal Hematite Nanorings

Single-crystal hematite (α- Fe 2 O 3) nanorings with three different thicknesses were synthesized by a hydrothermal method. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) show that the nanorings are single-crystal and have relatively uniform outer diameters of 160nm, and heights of about 100nm. Magnetic measurements up to 920K have been performed on hydrothermally synthesized α- Fe 2 O 3 nanorings and nanoparticles using a quantum design vibrating sample magnetometer. A high temperature phase transition of thermal stability (α- Fe 2 O 3 to Fe 3 O 4) occurs when magnetic measurement was performed under high vacuum (< 9.5 × 10-5 Torr). The phase transition temperature is 670K for nanorings with thickness of ∼30nm, 718K for nanorings with thickness of ∼50nm, 678K for nanorings with thickness of ∼65nm, and 640K for ∼35nm nanoparticles. This data show better thermal stability of nanorings with the thickness of ∼50nm than the other two kinds of nanoring samples The Néel temperature (T N ) of α- Fe 2 O 3 nanorings with the thickness of ∼50nm is determined to be 937.2K by magnetic measurement for the first time, about 22.8K below the bulk value. The small reduction of the T N of the α- Fe 2 O 3 nanorings is consistent with the finite-size scaling theory.

Effect of synthesis on structural and magnetic properties of cobalt doped Mn–Zn nano ferrites

A series of Co2+ doped Mn–Zn ferrite ceramics with the formula Mn0.5Zn0.5−xCoxFe2O4 (x=0, 0.25 and 0.50) have been successfully synthesized using polyethylene glycol-assisted co-precipitation and hydrothermal methods. The structural characterization of the samples has been done using room temperature X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD patterns revealed the formation of pure FCC spinel phase without any impurity peaks. SEM showed the uniform, homogenously spherical nanoparticles prepared from controlled reaction of hydrothermal method. Lattice constant found to be smaller for samples prepared from hydrothermal treatment. The average crystallite size of all nanoparticles were estimated using Scherrer’s formula and found to lie between 10–25±3nm with small size distribution of particles prepared by hydrothermal method. Bond length (A–O) and ionic radii (rA) at A-sites are smaller than the bond length (B–O) and ionic radii (rB) at B-sites for sample series prepared by two methods. Magnetic properties were studied using Physical Property Measurement System (PPMS), Quantum Design Vibrating Sample Magnetometer (VSM) option. Magnetic properties including saturation magnetization was higher (65emu/g for x=0.25) for hydrothermal treated samples. The method of preparation influenced the size of particle which in turn has strong affect on magnetic properties of prepared samples. The enhanced magnetic and structural properties of these nano ferrites made them a potential candidate to use in electromagnetic devices.

Effect of different doping on the structural, morphological and magnetic properties for Cu doped nanoscale spinel type ferrites

CuxM1−xFe2O4 (M=Co, Mn and Ni; x=0.0, 0.6 and 1.0) spinel type ferrite nanoparticles have been synthesized by cetyltrimethylammonium bromide (CTAB) assisted hydrothermal route using NaOH solution. The purity, structural characterization and magnetic properties have been investigated using the scanning electron microscopy, x-ray diffraction analysis and a quantum design vibrating sample magnetometer depending on the temperature. The scanning electron microscopy imaging exhibits very powerful aspect. The average size of composite nanoparticles for all samples was determined. Diameter of the samples is synthesized in nanoscale. The x-ray diffraction results have indicated that these samples are high phase purity, crystalline and inverse spinel ferrites. The temperature evolution of the magnetic properties and different doping effects for the samples have been observed. The pseudo spin-valve behavior has been showed for Cu0.6Co0.4Fe2O4 and CoFe2O4 samples. These samples can be considered as promising materials for magnetic recording media and electromagnetic absorbing technologies applications.

MAGNETIC PROPERTIES AND MÖSSBAUER SPECTRA OF Fe7S8 NANORODS

Fe7S8 nanorods have been successfully synthesized using a chemical evaporation method. X-ray diffraction pattern showed that the as-prepared products were Fe7S8 with no impurity phase. The results of scanning electron microscopy indicated that the samples synthesized at 750°C and 900°C were rod and sheet-like, respectively. The magnetic properties of the iron sulfide nanorods were measured over a wide temperature range (4 K–750 K) using a quantum design vibrating sample magnetometer. It was found that the nanorods were ferromagnetic with the Curie temperature of about 581 K. The Mössbauer spectra showed that the iron sulfide nanorods consisted of hexagonal pyrrhotites, whose spectra were asymmetrical according to correlation between the isomer shift and the hyperfine field.

Large-scale synthesis of Au–Ni alloy nanowires using electrochemical deposition

The template-assisted electrodeposition technique has been utilized to synthesize highly ordered, well-aligned, and dense Au–Ni alloy nanowires. The electrochemical impedance spectroscopy has been carried out to study the in situ growth process of alloy nanowires at different electrodeposition times. Their morphological studies have been carried out using the high-resolution transmission electron microscopy. Elemental composition of template-synthesized nanowires has been studied by energy dispersive X-ray analysis. The X-ray diffraction study revealed the face centered cubic structure of the nanowires. Magnetic properties of the nanowires have been studied using Quantum Design vibrating sample magnetometer.

Suppression of the Néel temperature in hydrothermally synthesized α-Fe2O3 nanoparticles

Magnetic measurements up to 1000 K have been performed on hydrothermally synthesized α-Fe2O3 nanoparticles (60 nm) using a Quantum Design vibrating sample magnetometer. A high vacuum environment (1×10−5 Torr) during the magnetic measurement up to 1000 K leads to a complete reduction of α-Fe2O3 to Fe3O4. This precludes the determination of the Néel temperature for the α-Fe2O3 nanoparticles. In contrast, coating α-Fe2O3 nanoparticles with SiO2 stabilizes the α-Fe2O3 phase up to 930 K, which allows us to determine the Néel temperature of the α-Fe2O3 nanoparticles for the first time. The Néel temperature of the 60-nm α-Fe2O3 nanoparticles is found to be 945 K, about 15 K below the bulk value. The small reduction of the Néel temperature of the α-Fe2O3 nanoparticles is consistent with a finite-size scaling theory.

High-temperature magnetic properties of noninteracting randomly oriented single-domain Fe 3 − δO 4 nanoparticles

Magnetic measurements have been performed on 40-nm sphere-like Fe 3 − δ O 4 ( δ = 0.043 ) nanoparticles using a Quantum Design vibrating sample magnetometer. Coating Fe 3 − δ O 4 nanoparticles with SiO 2 effectively eliminates magnetic interparticle interactions so that the coercive field H C in the high-temperature range between 300 K and the Curie temperature (855 K) can be well fitted by an expression for noninteracting randomly oriented single-domain particles. From the fitting parameters, the effective anisotropy constant K is found to be ( 1.38 ± 0.11 ) × 10 5 erg / cm 3 , which is very close to the bulk magnetocrystalline anisotropy constant of 1.35 × 10 5 erg / cm 3 . Moreover, the inferred mean particle diameter from the fitting parameters is in quantitative agreement with that determined from transmission electron microscope. Such a quantitative agreement between data and theory suggests that the ensemble of our SiO 2-coated sphere-like Fe 3 − δ O 4 nanoparticles represents a good system of noninteracting randomly-oriented single-domain particles.

NOVEL MAGNETIC PROPERTIES IN MULTI-WALLED CARBON NANOTUBE MATS: CONSISTENT WITH THE PARAMAGNETIC MEISSNER EFFECT DUE TO ULTRAHIGH-TEMPERATURE SUPERCONDUCTIVITY

We report magnetic measurements up to 1200 K on iron-contaminated multi-walled carbon nanotube mats with a Quantum Design vibrating sample magnetometer. Extensive magnetic data consistently show a ferrromagnetic transition at about 1000 K and a ferromagnetic-like transition at about 1275 K. The ferromagnetic transition at about 1000 K is associated with an Fe impurity phase and its saturation magnetization is in quantitative agreement with the Fe concentration measured by an inductively coupled plasma mass spectrometer. On the other hand, the saturation magnetization for the ferromagnetic-like phase (at 1275 K) is about four orders of magnitude larger than that expected from the measured concentration of Co or CoFe . We show that this ultrahigh-temperature ferromagnetic-like behavior cannot be explained by ferromagnetism of any Fe -carbon phases, carbon-based phases, or magnetic impurities, but is consistent with the paramagnetic Meissner effect (orbital ferromagnetism) due to the existence of π Josephson junctions in a granular superconductor.

Observation of an ultrahigh-temperature ferromagnetic-like transition in iron-contaminated multiwalled carbon nanotube mats

We report magnetic measurements up to 1200 K on multi-walled carbon nanotube mats using Quantum Design vibrating sample magnetometer. Extensive magnetic data consistently show two ferrromagnetic-like transitions at about 1000 K and 1275 K, respectively. The lower transition at about 1000 K is associated with an Fe impurity phase and its saturation magnetization is in quantitative agreement with the Fe concentration measured by an inductively coupled plasma mass spectrometer. On the other hand, the saturation magnetization for the higher transition phase ($\geq$1.0 emu/g) is about four orders of magnitude larger than that expected from the measured concentration of Co or CoFe, which has a high enough Curie temperature to explain this high transition. We show that this transition at about 1275 K is not consistent with a magnetic proximity effect of Fe-carbon systems and ferromagnetism of any carbon-based materials or magnetic impurities but with the paramagnetic Meissner effect due to the existence of $\pi$ Josephson junctions in a granular superconductor.