Onset of ferromagnetism in 3d-substituted FeAl alloys. I. Ti, V and Cr substitutions

The authors report structural and magnetic studies on series of FeAl alloys in which partial substitution of Al by a 3d transition metal has occurred. The solutes are Ti, V and Cr in the present paper. It is found that both Ti and V substitutions promote the establishment of double ordering, of the L2 1 type, whereas the Cr system remains B2 throughout. Metallographic observations confirm that only Ti alloys with x>or=0.35 contained significant quantities of any additional phases. The single-phase Ti and V alloys are paramagnetic, as anticipated on the basis of a simple electron concentration hypothesis and by analogy with equivalent CoGa alloys. However, the Ti alloys containing second-phase inclusions show a spontaneous magnetisation although the origin of this behaviour has yet to be ascertained. Ferromagnetism is observed in the Cr system beyond FeAl 0.65 Cr 0.35 and its onset is apparently presaged by a region of superparamagnetism and possibly a mictomagnetic region. The results are discussed in terms of current theories of magnetic moment formation.