Quadrupolar response from the crystal electric field level scheme consisting of only Kramers doublets in DyNiAl

The rare earth compound DyNiAl shows ferromagnetic and antiferromagnetic phase transitions at T_C = 30 K and T₁ = 15 K, respectively. Elastic properties of DyNiAl have been investigated by means of ultrasonic spectroscopy. The transverse elastic modulus C₄₄ shows an elastic softening below 60 K and exhibits a bend at T_C. The softening continues down to T₁ and an elastic hardening is observed below T₁. The softening above T_C is well reproduced by Curie-Weiss-type equation including a quadrupole interaction. A quadrupole-quadrupole coupling constant obtained from C₄₄ is negative, suggesting an antiferroquadrupolar-type interaction between quadrupoles O_yz or O_zx.