MAGNETISM AND HYPERFINE INTERACTIONS IN EuM₂Ge₂ AND GdM₂Ge₂(M equals Mn,Fe,Co,Ni,Cu).

X-ray, magnetic susceptibility and **1**5**1Eu, **1**5**5Gd Moessbauer effect studies of EuM//2Ge//2 and GdM//2Ge//2 were performed. All compounds crystallize in the ThCr//2Si//2 body centered tetragonal structure. In all compounds, except those with M equals Mn and in EuCo//2Ge//2, the M component carries no magnetic moment. All compounds except those with Mn are antiferromagnetic at low temperatures. In EuMn//2Ge//2 the Mn moments order ferromagnetically at 330 K and change to antiferromagnetic order when the Eu moments order ferromagnetically (9 K). This behavior is different from that in GdMn//2Ge//2, where the Mn sublattice orders antiferromagnetically at 365 K and becomes ferromagnetic and antiparallel to the ferromagnetic Gd sublattice at 96 K. The Moessbauer studies of **1**5**1Eu and **1**5**5Gd provide values for the magnetic hyperfine fields, the quadrupole interactions and the orientation of the magnetic moments relative to the local fourfold axis (c-axis).