Magnetic and structural properties of nanocrystalline ultrathin Fe83Cu1Nb7B9 submitted to Joule heating

Ultrathin (similar to 10 mu m) ribbons of the amorphous alloy Fe38Cu1Nb7B9 obtained by single roll melt spinning have been submitted to de Joule heating in vacuo in order to develop a nanocrystalline phase characterised by a very reduced grain size. The initial permeability of the nanocrystallized alloy was measured on open samples by means of a conventional fluxmetric technique with air-flux compensation. The interval of magnetising frequency was 100 Hz - 10 kHz. All samples were submitted to X-ray diffraction to evaluate the mean grain size, composition and strain level of the nanocrystalline phase. A substantial improvement in the magnetic permeability of Joule-heated nanocrystalline samples with respect to the conventionally annealed ones has been always found. Variations as high as 1000 times the as-quenched value have been observed for a wide range of electrical-current densities (4 10(7) less than or equal to j less than or equal to 6 10(7) A/m(2)).