Fermi surface topology and helical magnetic ordering in Gd-Y alloys

We present 3-dimensional Fermi surfaces reconstructed from 2DACAR projections for Gd70Y30 and Gd62Y38. There is an aparent lack of nesting feature in the Gd70Y30 which would be consistent with its ferromagnetic ordering at low temperatures. The Gd62Y38 alloy indicates nesting in a temperature regime where it orders in helical antiferromagnetic phase even in the presence of a magnetic field which forces ferromagnetic ordering. (orig.)