Field-induced magnetic structures in Tb₂ Ti₂ O ₇ at low temperatures: From spin-ice to spin-flip structures

We studied the field-induced magnetic structures of the Tb₂ Ti₂ O₇ pyrochlore by single-crystal neutron diffraction with a magnetic field applied along a [110] axis, focusing on the influence of a small misalignment. Both induced magnetic structures with k=0 and k= (0,0,1) propagation vectors are found to be sensitive to the misalignment, which controls the magnitude and orientation of the Tb moments involved in the β chains, with local [111] anisotropy axis perpendicular to the field. For k=0, spin-icelike structures are observed for a misalignment of a few degrees whereas other structures, where the Tb-β moments flip by "melting" on the field axis, occur when the field is perfectly aligned. The field evolution of the k=0 structure is well reproduced by a molecular field model with anisotropic exchange. We give a complete symmetry analysis of the k=0 and k= (0,0,1) magnetic structures, both being described by the basis functions of single irreducible representations.