Yüksel Köseoğlu

Microwave-induced combustion synthesis and characterization of NixCo1−xFe2O4 nanocrystals (x = 0.0, 0.4, 0.6, 0.8, 1.0)

A series of Ni-doped cobalt ferrites NixCo1−xFe2O4 (x = 0.0, 0.4, 0.6, 0.8, and 1.0) were prepared using microwave-induced combustion. Nickel, cobalt, and ferric nitrates were used as starting materials and glycine as fuel. The influence of Ni content on the lattice parameter, stretching vibrations, and magnetization was studied. XRD, FTIR, and SEM were used for structure, composition, and morphology investigation. A porous network structure was observed with average particle size 60–67 nm. All samples had a cubic spinel structure. The unit cell parameter “a” decreases linearly with nickel concentration due to the smaller ionic radius of nickel. Magnetization measurements showed that coercivity decreased as Ni content increased; it increased with decreasing temperature.

Synthesis and magnetic properties of octahedral ferrite NiχCo1−χFe2O4 nanocrystals

A series of Ni doped cobalt ferrite compounds with the formula NiχCo1−χFe2O4 where x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were prepared using a hydrothermal method and subsequently sintered/annealed at 600 °C for 3 h. The influence of the Ni content on the lattice parameter, a, stretching vibration and the magnetization of specimens were subsequently studied. XRD and FTIR were used to investigate structure and composition variations. All samples were found to have a cubic spinel structure. SEM was used to study morphological variations. The results indicate that the average particle sizes are between 30–35 nm with a narrow size distribution along with nanocrystals forming of regular octahedrons. A decrease in the peak to peak line width and increase in resonance field with increasing Ni content were observed from ESR measurements. Based on ESR results, a core-shell type of formation was proposed where the core is made up of undoped CoFe2O4 and the shell is Ni2+ doped CoFe2O4.

Energy absorption of superparamagnetic iron oxide nanoparticles by microwave irradiation

The main complexity in hyperthermia is generating and controlling the temperature distribution within tumor cells without damaging the normal tissue. Superparamagnetic iron oxide nanoparticles (SPIONs) with a diameter of 11nm were prepared by controlled coprecipitation and coated with oleic acid to prevent agglomeration and flocculation in the solvent. In situ monitoring of the temperature increment was performed to interpret the microwave absorption rate of the SPION dispersed in appropriate host media (polar or nonpolar solvents) during microwave irradiation. This approach allowed for the prediction of heating mechanisms as a result of the excitation of unpaired electrons of iron, effects of coating agents, particle size, and volume fraction (ϕ). The conversion efficiency from microwave irradiation to thermal energy was predicted by applying the conservation of energy to a differential volume. The rates of heat loss and energy absorption were obtained by nonlinear fitting of the experimental data.

Characterization of NiFe2O4 nanoparticles synthesized by various methods

Microwave-induced combustion with glycine, CTAB-assisted hydrothermal process with NaOH and NH3, EDTA assisted-hydrothermal methods have been applied to prepare NiFe2O4 nanoparticles for the first time. Structural and magnetic properties of the products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmison electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and electron spin resonance spectrometry (EPR). TEM measurements showed that morphology of the product depends on the synthesis method employed. The average cystallite size of NiFe2O4 nanoparticles was in the range of 14–59 nm as measured by XRD. The uncoated sample (Method A) had an EPR linewidth of 1973 Oe, the coated samples reached lower values. The magnetic dipolar interactions existing among the Ni ferrite nanoparticles are reduced by the coatings, which could cause the decrease in the linewidth of the EPR signals. Additionally, the linewidth increases with an increase in the size and the size distribution of nanoparticles.

Low temperature synthesis and characterization of Mn3O4 nanoparticles

Heating hydrous manganese (II) hydroxide gel at 85 °C for 12 hours produces Mn3O4 nanoparticles. They were characterized by X-ray powder diffraction (XRD) and infrared spectroscopy (FTIR). The particle size estimated from the SEM and X-ray peak broadening is approximately 32 nm, showing them to be nanocrystalline. EPR measurements confirm a typical Mn2+signal with a highly resolved hyperfine structure.

Oxovanadium(IV) complexes of bromo-and methoxy substituted N1,N4-diarylidene-S-methylthiosemicarbazones

Four new oxovanadium(IV) compounds were prepared by template reaction of salicyl-, 5-bromosalicyl-and 3-methoxysalicyl-aldehyde S-methylthiosemicarbazones with 2-hydroxy-, 5-bromo-2-hydroxy-and 3-methoxy-2-hydroxy-benzaldehyde in various combinations. The compounds were isolated as stable solid compounds with general formula [VO(L)] and characterized by elemental analysis, conductivity and magnetic measurements, electronic, IR and EPR spectroscopy. The X-band EPR signals recorded from powder forms of all samples have a single asymmetric line shape and theoretical fit studies proved the presence of axial symmetry around the paramagnetic vanadium ions. The anisotropic Lande splitting factors take values of g‖ < g⊥ < ge = 2.0023. Orbital energy levels for magnetic electrons were determined from theoretically well fitted Spin Hamiltonian parameters. The EPR spectra recorded from solution forms almost have isotropic character.

Synthesis of Co3O4 nanoparticles by oxidation-reduction method and its magnetic characterization

Without any surfactant, antiferromagnetic Co3O4 nanoparticles were synthesized successfully for the first time by means of an oxidation-reduction method with cobalt sulfate as starting material, which was oxidized to cobalt salt by NaNO3 after alkalinizing with NaOH. Morphological, structural, spectroscopic and magnetic characterization of the product were done by SEM, TEM, XRD, and VSM, respectively. The average crystallite size (on the base of line profile fitting method), D and σ, is estimated as 30 ± 6 nm. Some anomalous magnetic properties and their enhanced effect have been observed in Co3O4 antiferromagnetic nanocrystallites, including a bias field, coercivity, permanent magnetic moments and an open loop. These phenomena are attributed to the unidirectional anisotropy which is caused by the exchange coupling between AFM and FM layers, the existence of the spin glass like surface spins of Co3O4 nanoparticles due to size effects and surface-area effect.

Effect of MPEG Coating on Magnetic Properties of Iron Oxide Nanoparticles: An ESR Study

Metoxy polyethylene glycol (MPEG) coated and uncoated Fe3O4 (SPION) nanoparticles have been investigated by Electron Spin Resonance (ESR) technique at the temperature range between 10–300K. ESR measurements on powdered samples have been carried out by using X-band ESR Bruker EMX spectrometer. A strong and broad single ESR signal has been observed at all temperatures. Temperature dependence of ESR linewidth and resonance field is studied. The linewidth increases and the resonance field decreases by decreasing temperature while the ESR signal intensity remeains almost independent on the temperature. The shift in the resonance field value is a clear indication of the induced field (exchange anisotropy field), causing the frustration (disorder) of any magnetic system. A strong effect of coating on magnetic properties of SPION nanoparticles has been observed as well.

Magnetic Properties of an Intercalate Mn0.86PS3(ET)0.46: An ESR Study

MnPS3 intercalated with BEDT-TTF (ET) has been studied by Electron Spin Resonance (ESR) technique in the temperature range of 10–300K. A single and symmetric ESR peak was observed. The peak is much narrower than the expected from the paramagnetic Mn2+ ion. The ESR signal intensity, line width and effective g-value were observed to change dramatically at about 45 K, indicating a magnetic phase transition. That is, while the intensity is monotonically increased until a critical temperature Tc=45 K, both the line width and g-value remain almost constant above Tc. However, a very sharp decrease in ESR signal intensity, accompanied by line broadening below Tc, indicates a very strong spin frustration at lower temperatures. Some small and relatively smooth changes also occurred at about 30 K, 100 K and 170 K. However, below 30 K, the magnetization however starts to increase again and the line-width decreases with decreasing temperature. This points to the onset of a second transition toward ferromagnetic phase.