The magnetic structures of the alloys Au2(Mn, Al)2

Neutron diffraction studies of the alloy system Au 2 Mn 2 - l Al l have established the coexistence of antiferromagnetic and ferromagnetic structures in between the extreme compositions of Au 2 Mn 2 and Au 2 MnAl. The magnetic moment of the manganese atoms remains throughout close to 4 2 μ B . Both slow-cooled and quenched samples have been examined and the neutron conclusions have been largely correlated with concurrent measurements of bulk magnetization, explaining in particular the low values of μ B , to which the latter measurements invariably lead. It is shown further that the attainment of perfect Heusler-type ordering, near the composition Au 2 MnAl, causes the appearance of a spiral-spin structure for which the spiral axis is parallel to a cube edge. Roughly a half of the material may appear with this new structure, which has a Néel temperature of 64 °K and in which the manganese moment is again close to 4.2 μ B .