Investigation of the Magnetic Aftereffect in Dilute FeNi Alloys after Low-Temperature Neutron Irradiation

Dilute Fe alloys containing up to 0.5 at% Ni, neutron-irradiated at 77 K, exhibit a very complicated relaxation spectrum during anneal in the temperature range 30 to 350 K. This behaviour, in which individual peaks transform from one into another, is investigated in detail. All maxima occurring in the temperature range 30 to 140 K are found to be of Debye-type with relaxation times obeying an Arrhenius equation τ = τ0 exp (Q/kT). The major processes of these spectra are computer-analysed in order to determine their activation parameters Q and τ0. The complicated peak genealogy, as observed on anneal, is attributed to the presence of two configurations of reorientating Fe interstitial atoms which form small clusters together with substitutionally and interstitially dissolved Ni atoms.