Quadrupolar Interaction in NdB₆ Studied by Magnetostriction

Abstract

Thermal expansion and longitudinal magnetostriction along the ‹ 001› direction Δl/l_{‹ 001›} of NdB₆ have been measured in the magnetic field H along the z axis (‹ 001› direction) up to 8, T. Below the Néel temperature T_N, accompanying the spin-flop transition or domain rotation at 0.5, T, the z axis shrinks greatly. The thermal expansion in H=2.1, T, where the ordered moment is perpendicular to H, shows that the shrinkage of the z axis becomes smaller with increasing temperature and disappears at T_N. The results were analyzed using a molecular field approximation and it was shown that it is necessary to introduce the ferro-quadrupolar interaction K₃ with a Γ₃ symmetry in NdB₆. The difference in the thermal expansion in the paramagnetic region between CeB₆ and NdB₆ is discussed from the standpoint that there exists large antiferro-quadrupolar short-range ordering in CeB₆.