Crystal and magnetic structures of TmFe2Si2 and TmNi2Ge2 compounds. Influence of the d-metal charge on the anisotropy direction of the RT2X2 (R = rare earth, T = 3d or 4d metal and X = Si, Ge) compounds

Neutron diffraction experiments have been performed on the TmFe2Si2 and TmNi2Ge2 compounds in order to determine their crystal and magnetic structures. Both crystallize in the tetragonal ThCr2Si2-type with space group I4/mmm. The first is ferromagnetic and the second antiferromagnetic with magnetic propagation vector q=(0, 0, 0.7854) at 1.5 K. No magnetic moment was detected on the iron or nickel sublattice. The direction of the Tm3+ magnetic moment is perpendicular to c. Crystal field calculations, based on the point charge model, show the influence of the d-metal charge on the anisotropy direction of the RT2X2 compounds. (orig.)