Superlattice dislocations and magnetic transition in Fe-Al alloys with the B2-type ordered structure

Abstract

Magnetization was measured in plastically deformed 34.0, 36.2 and 40.0 at.% Al-Fe alloys with the B2 structure in the temperature range from 77 K to room temperature. At 34.0 at.% Al concentration, the spontaneous magnetization, Ms, increases considerably as a result of 4% strain and has a broad maximum at about 200 K, which would result in mictomagnetism. The Fe-Al alloys containing 36.2 and 40.0 at.% Al are paramagnetic before plastic deformation and as a result of plastic deformation the magnetic susceptibility, chi , increases remarkably and at the same time Ms appears. The Curie temperature, TC, becomes higher with increasing strain. Superlattice dislocations were observed by use of an electron microscope A (111) superlattice dislocation is separated into two (1/2) (111) superpartials coupled by a ribbon of antiphase boundary (APB). The APB width is 28 to 35 nm. The dislocation density, rho , is 109 to 1010 cm-2. The relation between Ms and rho which is calculated by a simple localized moment model is compared with the experimental results. The change of TC and the increase of chi suggest the existence of a long-range influence between ferromagnetic clusters as far as 102 nm.