Magnetic phase diagrams of Y-diluted antiferromagnet Tb_1-xY _xB₂C₂ (0.2 ≤ x ≤ 0.5)

Magnetic B-T phase diagrams were examined by magnetization and specific heat experiments on the single crystalline Tb_1-xY_xB ₂C₂ (0:2 ≤ x ≤ 0:5) compounds, and neutron diffraction experiments was performed on the powder Tb_0.5Y _0.5 ¹¹B₂C₂ sample. The magnetization curves evidence that the fieldinduced transition occurs from phase IV into phase II′ through a mixed phase of both phases, where phase IV is antiferromagnetic and phase II′ is a field-induced phase with the antiferromagnetic and antiferroquadrupolar order. The mixed phase (IV + II′) is enhanced by the Y-dilution, and the lower and upper verges of the mixed phase become clearer in the differential magnetization dM=dB-B curves. The Y-dilution results in scaling down of the ordered phases regions in the B-T space. The ways of scale down of the ordered phase are different between two field directions along the tetragonal [100] and [110]-axes, that is, the anisotropy of phase stability is increased by the Y dilution. It is supposed that the enhancement of anisotropic phase stability by the Y dilution may be due to the symmetry of the multipoles and the anisotropic multipolar interactions weakened by the Y dilution.