Effects of Y Dilution on the Antiferroquadrupolar Ordering in the Tetragonal Compound DyB_<b>2</b>C_<b>2</b>

Abstract

Antiferroquadrupolar (AFQ) and magnetic transitions in Dy 1- x Y x B 2 C 2 (0≤ x ≤0.6) have been investigated on the single-crystalline samples by magnetization and specific heat measurements. As the Y concentration increases, the magnetic transition temperature decreases from 15.3 K at x =0 to 4.5 K at x =0.6. The AFQ transition temperature also decreases from 24.7 K at x =0 to 7.4 K at x =0.6, although it becomes unclear for x ≥0.5 in the magnetization. A λ-type peak of specific heat at T Q becomes broader as x increases, and changess to a small upheaval for x ≥0.5. On the other hand, the field-induced transitions at the boundary between the AFQ and paramagnetic phases are clearly observed in the magnetization processes at 1.5 K x ≤0.6. The behavior of specific heat implies that the AFQ interaction acts strongly in a rather shorter distance than the antiferromagnetic interaction in DyB 2 C 2 . The Y dilution causes in a wide distribution of the AFQ interaction strength acting on the Dy quadrupoles. Then the AFQ order developes in a wide temperature range, and is almost completed above the magnetic transition temperature.