A comprehensive analysis of magnetoimpedance (MI) phenomena in Fe-based nanocrystalline ribbons is presented in this paper. Giant MI responses have been observed in nanocrystalline samples annealed over the temperature range 490 and 600 • C. More than 400% increases of the MI ratio were obtained both in Fe 73.5 CuNb 3 Si 13.5 B 9 and in Fe 88 Zr 7 B 4 Cu ribbons. The sensitivity can reach a value larger than 60% Oe −1 in the field range 3-7.2 Oe at 800 kHz for Fe 73.5 CuNb 3 Si 13.5 B 9 ribbons. No MI effect was observed in an as-quenched amorphous Fe 88 Zr 7 B 4 Cu sample, because of its very low permeability. A mostly resistive feature was found in an as-quenched amorphous Fe 73.5 CuNb 3 Si 13.5 B 9 sample. The field dependences of the effective permeability show a typical transverse anisotropy property, and the development of the transverse anisotropy in naturally annealed Fe-based ribbons was analysed.
The Sm substituting effects for La in La0.67Ca0.33MnO3
have been studied systematically. With increasing Sm doping amount, the metal-isolator
phase transition temperature for the samples decreases monotonically, the corresponding
peak resistivity increases dramatically and the Curie temperature decreases
monotonically. The substitution of La-Ca-Mn-O with 0.13% Sm for La improved the
magnetoresistance ratio by an order of magnitude. The effects of doping with Sm can be
explained in terms of the lattice effects. An irreversible MR behaviour was observed in
the Sm-doped compound. This effect was enhanced with increasing Sm doping amount.
Magneto-impedance (MI) effects have been observed in amorphous and nanocrystaUine F43.5 Cu Nb3Si13.5B9 ribbons. Large MI values have been obtained in nanocrystalline samples (NCS), but not in as-quenched samples (AQS). The magnetic responses of impedance of nanocrystalline samples share some common features with that of Co-based amorphous wire and ribbon samples. The field dependencies of effective permeability for nanocrystalline samples have shown, a sharp change a t the anisotropy field. The effective permeability and the hysteresis loops for AQS and NCS have been shown to be responsible for their MI effects. The sensitivity of the magnetic responses in the nanocrystalline sample can reach 50%/Oe.
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