Irradiation-induced amorphized state of rapidly quenched R 12Fe82B6 alloys (R = Nd, Er)

Rapidly quenched (RQ) alloys R ₁₂Fe₈₂B₆ (R = Nd, Er) have been prepared by melt spinning. Their magnetic properties, structure, and phase composition have been studied before and after fast-neutron irradiation to a fluence of 1.2 × 10²⁰ n/cm². Before irradiation, it is the Nd₂Fe₁₄B-type phase (space group P4₂/mnm) that is mainly present in the RQ alloys at 295 K. In the Nd₁₂Fe₈₂B₆ alloy, this phase has a ferro-magnetic structure with magnetic moments at the Nd and Fe atoms oriented parallel to the c axis; the Er₂Fe₁₄B phase found in the Er₁₂Fe₈₂B₆ alloy is characterized by a ferrimagnetic order of Er and Fe magnetic moments parallel to the basal plane. After irradiation, the crystalline state of both RQ alloys transforms into an amorphous state. The ferro- and ferrimagnetic orders are retained in them, but the Curie temperature of the alloys with Nd and Er decreases by 100 and 200 K, respectively. The spontaneous magnetization of the irradiated alloys at 5 K is approximately equal to their magnetization in the crystalline state, whereas their coercive force is lower than that for the alloys before irradiation by two orders of magnitude. The effects observed are explained by the dispersion of Fe-Fe exchange interactions resulting from the dispersion of interatomic spacings in the amorphous alloys.