SOME STRUCTURAL ASPECTS OF MAGNETIC PROPERTY EVOLUTION IN FINEMET-TYPE SENSOR MATERIAL DURING AMORPHOUS-NANOCRYSTALLINE TRANSFORMATIONS

Devitrification of glassy Fe73.5Si13.5B9Nb3Cu1alloy used as potential sensor material was followed by magneticmeasurements and X-ray diffraction, and transmission electron microscopy. Itwas found, that the permeability, and the coercive field of the alloychanged well below the crystallisation onset, showing a remarkable increase,which was attributed to the structural relaxation and a heterogen nucleationof iron rich phase on Cu clusters. On the basis of lattice parametermeasurements the iron rich clusters were depleted from Si atoms during thenucleation process and the Si atoms built in them only during annealing athigher temperatures as 500 \circC and 540 \circC forming aDO3 structure.From the structural study of samples annealed near to the optimaltransformation stage it was concluded, that size distribution of thebcc-Fe(Si) nanocrystallites (not exclusive factor) was only one of the mostimportant factors to achieve the optimal soft magnetic properties, but at thesame time, their volume fraction, as well as the degree of ordering inDO3 structure did also contribute to the property optimization.The average grain size produced by laser pulse heat treatment was nearly thesame, as that obtained during the traditional heat treatments.