Spontaneous magnetizations and phase diagram of Dy1-xGdxB2C2

Tetragonal DyB2C2 undergoes an antiferroquadrupolar (AFQ) order transition at TQ=24.7K and a successive antiferromagnetic (AFM) transition at TN=15.3K. Gd (L=0, S=72) substitution for Dy strengthens AFM interaction and weakens AFQ interaction. At x=0.2, TN becomes higher than TQ and a new AFM phase (phase IV) appears between them. For 0.25=<x, no AFQ transition occurs. The spontaneous magnetization that is characteristic to the ground state (phase III) of DyB2C2 suddenly disappears at a Gd content between x=0.2 and 0.25. This fact implies that there exists the phase boundary at 0.2<x<0.25 where phase III changes into phase IV