Spontaneous magnetizations and phase diagram of [formula omitted

Abstract

Tetragonal DyB 2C 2 undergoes an antiferroquadrupolar (AFQ) order transition at T Q = 24.7 K and a successive antiferromagnetic (AFM) transition at T N = 15.3 K . Gd ( L = 0 , S = 7 2 ) substitution for Dy strengthens AFM interaction and weakens AFQ interaction. At x = 0.2 , T N becomes higher than T Q 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 DyB 2C 2 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.