Changes of the magnetic interactions in TlCo2Se2 upon metal substitution

Abstract Various solid solutions TlCo 2− x Me x Se 2 (Me=Fe, Ni and Cu) have been investigated by neutron powder diffraction, supplemented by magnetometry. The incommensurate spin-helix running along the c -axis in tetragonal TlCo 2 Se 2 prevails for low concentrations of copper and iron but changes pitch. In the copper case, only cobalt carries a magnetic moment. On nickel substitution, however, collinear antiferromagnetic coupling between the ferromagnetic layers occurs. The magnetic moment distribution between the two transition metals in the solid solution TlCo 2− x Ni x Se 2 was tentatively probed with first principle calculations on fictive ordered TlCoNiSe 2 , modelled by two types of superstructures. Also the ternary mother compounds, Pauli paramagnetic TlNi 2 Se 2 and antiferromagnetic TlCo 2 Se 2 , were investigated with the same LMTO method.