From ferromagnetism to incommensurate magnetic structures:: A neutron diffraction study of the chemical substitution effects in TbPt1-xCux -: art. no. 184425

We report the magnetic structures of the TbPt1-xCux system obtained by means of neutron diffraction experiments. Symmetry analyses have been carried out for the R3+ magnetic site. The compounds with copper concentrations x<0.3 present the same magnetic structure than the extreme TbPt, which is of noncollinear ferromagnetic type, -CxFz; on the contrary, for copper concentrations 0.3<0.5, we found incommensurate amplitude-modulated structures in which the moment modulus varies sinusoidally with a propagation vector along the b-axis. For concentrations x>0.5, the propagation vector lies in the ac-plane being the structure also amplitude-modulated. For the intermediate compound, TbPt0.7Cu0.3, we observe an evolution from an amplitude-modulated incommensurate structure to a noncollinear commensurate one, -CxFz, that remains stable down to very low temperatures. The different kinds of magnetic ordering in the TbPt1-xCux series, along which the volume remains constant, are discussed in terms of the competition between RKKY interactions and magneto-crystalline anisotropy, and they are compared to those observed in TbNi1-xCux.