The magnetic specific heat of GdΝi 2 Sn2 , GdΝi2 Sb2 and GdCu2 Sb2
shows a λ-type anomaly at TN with a noticeable reduction of the discontinuity
compared to that expected for a simple antiferromagnet. It can be
associated with the existence of amplitude modulated magnetic structure
just below TN. Above TN a weak magnetic contribution is observed, evidencing
the short-range ordering. From neutron diffraction studies it can be also
concluded that investigated compounds have not simple antiferromagnetic
structures. For GdΝi2Sn2 the propagation vector Q = (0.3, 1/2, 1/2) was
found with the magnetic moments along the [1,0,0] axis
