Elastic moduli of the distorted Kagome-lattice ferromagnet Nd₃Ru₄Al₁₂

The distorted kagome-lattice compound Nd₃Ru₄Al₁₂ has the hexagonal structure. This compound is reported as a ferromagnet in which spins are aligned along the c-axis with the Curie temperature T_c = 39 K. The nature of localized f-electrons is expected in Nd₃Ru₄Al₁₂, and magnetic anisotropy can be attributed to a crystal electric field (CEF) effect. We performed ultrasonic measurements on a Nd₃Ru₄Al₁₂ single-crystalline sample in order to investigate the phase transition at T_C and the CEF effect. All longitudinal and transverse elastic moduli increase monotonically with decreasing temperature, and no clear elastic softening due to a quadrupole interaction is detected under the hexagonal CEF. This result is in contrast to an isomorphic compound Dy₃Ru₄Al₁₂ with a remarkable elastic softening of the transverse modulus C₄₄. At the ferromagnetic phase transition, the moduli show obvious elastic anomalies, suggesting characteristic couplings between a strain and a magnetic order parameter.