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

Abstract
Ultrathin (- 10 µm) ribbons of the amorphous alloy Fe₈₃CU₁Nb₇B₉ obtained by single roll melt spinning have been submitted to do 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 (4.10⁷ ≤ j ≤ 6.10⁷ A/m²).