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

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Abstract
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 L21 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 FeAl0.65Cr0.35 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.