Pressure effects on the magnetic character of TbM1-xCux (M = Pt, Ni)

High pressure and controlled chemical substitution studies become complementary methods in the understanding of the basic magnetic interactions in solids. They provide a powerful tool for giving new insights to former theoretical magnetic models by establishing the influence of electronic and crystalline variations on the magnetic order of such compounds. In this work, we present the neutron diffraction studies under pressure up to 65 kbar on the series TbPt1-xCux and TbNi1-xCux. At ambient pressure, a change from a ferromagnetic behavior to an antiferromagnetic one induced by increasing Cu concentration can be observed in both systems, while there is no volume variation in the Pt-based series and with a change of 4% in the Ni-based one. For those compounds with lower Cu contents non collinear ferromagnetic structures were determined (-CxFz for the Pt-based series and FxCz for the Ni one), whereas incommensurate magnetic structures appeared for Cu concentrations higher than 35%. We found that the applied pressure favours antiferromagnetism in both series by inducing an inner moment reorganisation. In this sense, the antiferromagnetic component of the non-collinear ferromagnetic structures is enhanced with pressure. In addition, in the antiferromagnetic compounds the strong decrease of the intensity of the first peak in the diffraction pattern associated to the incommensurate structures seems to indicate an evolution to a pure antiferromagnetic phase in the cell. (author)