Structural and magnetic properties of Co(AlV) alloys

Abstract

Magnetization and magnetic susceptibility measurements have been made over a wide range of temperature for the alloy series CoAl1−xVx for 0≤x≤0.5. Neutron diffraction measurements have also been made at room temperature using the Rutherford Appleton Laboratory spallation source (ISIS). The observed intensities suggest that for x≤0.25 the structure is the singly ordered B2 (CsCl) structure with the V atoms occupying Al sites. Beyond this concentration a model in which double ordering of the L21 (Heusler) type with the V atoms favoring one of the two equivalent Al sites seems consistent with the results. The magnetization measurements indicate that the series becomes ferromagnetic for x>∼0.1 with the intrinsic magnetization σ rising to a maximum of ∼50 emu. g−1 at x=0.5 for which the Curie temperature TC is ∼320 K. The inverse susceptibilities are generally linear with temperature and almost independent of concentration for x>0.2, suggesting an itinerant interpretation. The maximum values of TC and σ reached are less than half those achieved in the corresponding CoAl1−xMnx system but comparable with those seen in the CoAl1−xCrx system. Comparisons with the isoelectronic CoGa system are drawn. The results have relevance to theoretical estimates of impurity moments in CoAl and CoGa.