Non-collinear magnetic structures of TbCoO3 and DyCoO3

The orthoperovskites TbCoO3 and DyCoO3 with Co3+ in a non-magnetic low-spin state have been investigated by neutron diffraction down to 0.25 K. Magnetic ordering is evidenced below T-N = 3.3 K and 3.6 K, respectively, and the ordered arrangements are of canted type, A(x)G(y) for TbCoO3 and G(x)A(y) for DyCoO3 in Bertaut's notation. The experiments are confronted with the first-principle calculations of the crystal field and magnetism of Tb3+ and Dy3+ ions, located in the Pbnm structure on sites of C-s point symmetry. Both these ions exhibit an Ising behavior, which originates in the lowest energy levels, in particular in accidental doublet of non-Kramers Tb3+ (4f(8) configuration) and in ground Kramers doublet of Dy3+ (4f(9)) and it is the actual reason for the non-collinear AFM structures. Very good agreement between the experiment and theory is found. For comparison, calculations of the crystal field and magnetism for other systems with Kramers ions, NdCoO3 and SmCoO3, are also included. (C) 2013 Elsevier Masson SAS. All rights reserved.