Neutron irradiation effect on permeability and magnetoimpedance of amorphous and nanocrystalline magnetic materials

In this paper we provide physical insights into the effect of neutron irradiation on permeability spectra and magnetoimpedance of amorphous and nanocrystalline alloys. Experimental results indicate that neutron irradiation increases the permeability of the amorphous alloy but decreases the permeability of the nanocrystalline alloy in a high frequency region $(f⩾1\mathrm{MHz})$, while the opposite is found in a low frequency region $(f<1\mathrm{MHz})$. A careful examination of sample temperature during neutron irradiation process excludes thermal annealing as a possible origin of the observed irradiation effect. The magnetic relaxations in the low and high frequency regions are ascribed to the irreversible domain wall motion and reversible rotational magnetization, respectively. The enhancement in the permeability of the amorphous alloy upon neutron irradiation leads to a parallel improvement of magnetoimpedance response of the material, which is of practical use for sensing applications.

Figure 1

(a) The real and (b) imaginary parts of the permeability spectra of as-quenched ${\mathrm{Fe}}_{73.5}{\mathrm{Cu}}_1{\mathrm{Nb}}_3{\mathrm{Si}}_{13.5}{\mathrm{B}}_9$ sample under different ac fields.

Figure 2

Changes in initial permeability attributed to the domain wall motion $\left({\mu }_{lo}\right)$ and rotational magnetization $\left({\mu }_{hi}\right)$ as a function of fast neutron fluence. Symbols: open and solid square for experimental data, and solid lines for fitting curve using $\mu ={\mu }_0\exp (-\mathrm{g}\sigma \epsilon \varphi \mathrm{t})$ in Ref. 3.

Figure 3

Hysteresis loops of (No. 1) as-quenched and (No. 3) neutron irradiated samples.

Figure 4

The measured magnetoimpedance ratio $(\Delta Z∕Z)$ as a function of frequency. (No. 1) the as-quenched alloy, (No. 2) the alloy annealed at 473 K, (No. 3) the neutron irradiated amorphous alloy, (No. 4) the alloy annealed at 823 K, and (No. 5) the 823 K-annealed and neutron irradiated alloy.