Seminars Archive

Nanostructured magnetic materials: particle size and interparticle interactions effect

Abstract
The size effect on the properties of magnetic materials is discussed. The magnetic properties change dramatically at nanometer length scale (less than 100 nm ), giving rise to new phenomena, very interesting from both fundamental and technological point of view. The grain size of nanostructured materials is far below the usual size of magnetic domains and is in the same range or even below the thickness of Bloch-walls. Therefore, one can expect that the intrinsic magnetic properties, such as the saturation magnetization Ms(T) and the magnetocrystalline anisotropy constant Ka, become particle size dependent when the size is decreased to the nanometer range. Giant magnetoresistance effects have been found in nano-granular immiscible metallic alloys ( e.g. Co-Cu, Fe-Ag ), opening new perspectives in the area of recording heads and magnetic field sensors. The soft and hard magnetic properties are found to be strongly enhanced in nanocrystalline materials. Nanocrystalline Fe-based alloys produced by controlled crystallization of the amorphous ribbons show excellent soft magnetic properties. Nanocrystalline hard rare earth-based alloys (e.g. Nd12Fe14B) and nanocomposite magnetic materials, consisting of a mixture of exchange coupled magnetically hard and soft a-Fe or Co phases, exhibit enhanced remanence and represent a new generation of permanent magnets. Both the enhanced soft and hard magnetic properties are determined by the exchange interactions at the interface between nanograins.