Vladimir Kolesnichenko

Magnetic properties of ultrafine cobalt ferrite particles

We have studied magnetic properties of a diluted system of ultrafine cobalt ferrite nanoparticles (d∼3.3 nm). From the peak of the zero-field-cooled measurements, we obtained the blocking temperature TB of about 90.5 K and it is virtually independent of the applied magnetic field up to 5 kOe. At the superparamagnetic region T>TB, the system follows the modified Curie-law variation of the magnetic susceptibility χ=χo+C/T. We observed that the saturation magnetization follows a spin-wavelike temperature dependence at temperature above 10 K. In spite of the cubic structure for cobalt ferrite, at 2 K, the reduced remanence Mr/Ms is equal to 0.46 which is close to the theoretical value of 0.5 expected for noninteracting uniaxial single-domain particles with the easy axis randomly oriented. From the ac susceptibility measurements at different frequencies, we obtained a linear dependence of the logarithm of the experimental time window τex as function of inverse blocking temperature (1/TB). The fitting results i...

Superparamagnetic Iron Oxide Nanoparticles with Variable Size and an Iron Oxidation State as Prospective Imaging Agents

Magnetite nanoparticles in the size range of 3.2-7.5 nm were synthesized in high yields under variable reaction conditions using high-temperature hydrolysis of the precursor iron(II) and iron(III) alkoxides in diethylene glycol solution. The average sizes of the particles were adjusted by changing the reaction temperature and time and by using a sequential growth technique. To obtain γ-iron(III) oxide particles in the same range of sizes, magnetite particles were oxidized with dry oxygen in diethylene glycol at room temperature. The products were characterized by DLS, TEM, X-ray powder diffractometry, TGA, chemical analysis, and magnetic measurements. NMR r(1) and r(2) relaxivity measurements in water and diethylene glycol (for OH and CH(2) protons) have shown a decrease in the r(2)/r(1) ratio with the particle size reduction, which correlates with the results of magnetic measurements on magnetite nanoparticles. Saturation magnetization of the oxidized particles was found to be 20% lower than that for Fe(3)O(4) with the same particle size, but their r(1) relaxivities are similar. Because the oxidation of magnetite is spontaneous under ambient conditions, it was important to learn that the oxidation product has no disadvantages as compared to its precursor and therefore may be a better prospective imaging agent because of its chemical stability.

Fabrication and properties of magnetic particles with nanometer dimensions

Novel nanocrystalline inorganic materials ranging from metals to ternary metal oxides and fluorides have been synthesized in aqueous solutions with restricted environment of reverse micelles. This technique allowed also sequential synthesis leading to a core–shell type structure. Methods of synthesis of nanoparticles of magnetic metals Fe, Co and alloys FePtX and CoPtX coated with gold, metal ferrites MFe2O4 (M=Mn, Fe and Co) and antiferromagnetic fluoromanganites NaMnF3 and KMnF3 have been developed. The synthesized materials were characterized using X-ray diffractometry, TEM microscopy with EDAX analysis and SQUID magnetometry. Novel physical properties of these materials are discussed with emphasis given to the differences between course and fine-grained magnetic materials.

Synthesis and Manipulation of Nanophase Magnetic Materials

Synthesis of various types of inorganic materials, namely metals, ternary metal oxides (ferrites), cadmium sulfide (doped with Mn) and alkaline trifluoromanganates, in their nanocrystalline state is performed in aqueous solutions. Restricting conditions for crystal growth were provided using reverse micelle water-in-oil microemulsions technique. The obtained materials have been characterized using electron microscopy TEM imaging, X-ray diffractometry and SQUID magnetometry. nanoparticles reverse micelles superparamagnetics ferrites ferromagnetic metals metal sulfides metal fluoromanganates

RF dynamics in nanoparticle systems with tuned strength of interactions

Summary form only given. The dynamics of magnetic nanoparticle systems is a subject of considerable interest due to their fundamental and technological interest. The properties of such systems are strongly modified compared to the bulk, due to granular texture and the small size of the grains. In this paper we present a study on the magnetic properties of different samples of Co nanoparticles dispersed in different volume fractions in a wax matrix. Structural and morphological analysis of the Co nanoparticles systems was performed by TEM and light scattering experiments. RF transverse susceptibility (TS) experiments at various temperatures, ac susceptibility in the frequency range (10 Hz, 10/sup 4/ Hz) and various field and temperature dependent magnetization processes were used in order to investigate dynamics in nanoparticle systems. In the paper the experimental observed effect of inter-action on TS curves is very well explained by a new micromagnetic model of TS based on the Landau-Lifshitz-Gilbert equation.