Different mechanisms of anelastic and ferromagnetic relaxation due to defects in neutron irradiated iron

Anelastic and magnetic relaxations of point defects in iron were studied with different techniques in an inverted torsion pendulum: internal friction (1 Hz), elastic aftereffect and magnetoelastic aftereffect. They are compared with magnetic aftereffect measurements. For the nitrogen Snoek relaxation the results of all techniques agree with respect to the relaxation time, which follows an Arrhenius equation, the parameters of which can be determined with high precision. This agreement exists also for most of the relaxation peaks in neutron irradiated iron. However, there is a prominent peak (II2* at 155 K (1.4 Hz)), for which different results are obtained with anelastic and magnetic relaxation experiments. This II2*-relaxation is suggested to originate from a complicated configuration of a multiple self-interstitial atom, relaxing with two relaxation times and interacting differently with elastic stresses and the magnetostrictive forces. It is furthermore discussed why for nitrogen as well as for the II2*-defect magnetic after effect and magnetoelastic damping follow the same relaxation time, though the microscopic mechanisms controlling them are quite different (reversible and irreversible displacements of domain walls). (author)