National project (2006-2010)

Project’s subject is research of the magnetic properties of nanosized materials that can be generally described as 3d and/or rare earths oxides. The following nanosystems will be considered:

a) spinel structure oxides:

(i) ferrites (pure and mixed) of the general formula MFe2O4 (M=Zn,Co,Mn,Ni);

(ii) manganates LiMn 2-xM xO4 (M=Zn,Cr,Ti);

b) manganites of the general formula R 1-xMxMnO3 (R=rare earth, M=Ca,Ba,Sr);

c) pure and mixed rare earth oxides (R’,R”)O3 (R=rare earth);

d) magnetic nanocomposites – magnetic nanoparticles embedded in the diamagnetic nonmetallic matrix (for inst. alpha -, gamma -, epsilon -Fe2O3 /SiO2 ), or in a polymer host (for inst. (Ni,Fe)-PVA).

Research will be aimed towards the influence of the different methods/routes of synthesis on the composition, nanostructural, microstructural and crystallochemical properties of the obtained materials, as well as towards the correlation among these properties and magnetic behavior. For the sake of comparative analysis the polycrystalline counterparts of the above materials will be also synthesized.

The research description can be divided into several interconnected parts:

1. Synthesis, structure, microstructure and crystallochemistry – To synthesize the above quoted materials several methods will be used: sol-gel, glycine-nitrate, micromicelles, and mechanochemistry. Some samples will be synthesized by several different methods in order to obtain different particle size, distribution and morphology, as well as different structural and microstructural parameters. Characterization of these parameters will be done by TEM/SEM microscopy, and by x-ray and neutron diffraction. Special attention will be devoted to the analysis of the diffraction lines broadening in order to determine microstructural parameters (crystallite dimension, microstrain and anisotropy) that are important for the analysis of magnetic properties.

Another important aspect is investigation of the influence of the synthesis methods and parameters on the crystallochemical properties of the samples: cationic distribution, stoichiometry, and change of chemical composition with partial cationic replacement. Precise determination of these parameters is of key importance for the analysis of their correlations with magnetic properties.

2. Magnetic properties of the nanoparticle magnetic materials – We shall perform systematic measurements of many magnetic properties and analyze their correlations with structural, microstructural and crystallochemical characteristics. By measuring magnetization, hysteresis, and AC susceptibility in the broad rage of temperatures, magnetic field strengths and frequencies (using SQUID magnetometer) we shall obtain data on many magnetic properties of nanoparticle systems: magnetic moments, exchange integrals, coercive fields and remanent magnetization, blocking temperatures, magnetic transition temperatures, and anisotropy constants. These data will be used in determination of the static and dynamic magnetic properties, and in combination with the neutron diffraction data and measurements of magnetoresistivity they will enable the construction of magnetic phase diagrams. This is especially important for the complex systems such as colossal magnetoresistance (CMR) manganites. The final goal is to design the application oriented system that possesses the highest magnetoresistivity ratio obtained in the lowest possible magnetic fields, together with the high Curie temperature.

Magnetic properties of nanosystems are also governed by the inter/intra particle interactions of the dipol-dipol and/or exchange type. These interactions will be investigated both on nanopowder samples and nanocomposites (by changing the magnetic particle dilution) in order to reveal their quantitative and qualitative features.

Above mentioned magnetic measurements will be supplemented with the following experiments that will be done through existing international cooperation: neutron diffraction ( Uppsala University , Sweden ); high magnetic fields (CNRS Grenoble, France); Mossbauer spectroscopy (USP, Brazil ); Raman spectroscopy (CNRS UMR, France).

Importance of the project:

(i) Scientific – To establish synthesis methods/routes that produce well defined nanosystems; to understand and systematize correlations among microstructural, crystallochemical and magnetic properties;

(ii) Applicative – To design magnetic nanosystems with optimal characteristics for prospective applications.