Ultrasonic Investigation of the Magnetic Ordering in Er₃Ru₄Al₁₂ with a Distorted Kagome Lattice

To investigate a phase transition around 2 K in Er₃Ru₄Al₁₂ with a distorted kagome lattice, we conducted the specific heat, magnetic susceptibility, and ultrasonic measurements. At zero field a sharp peak of the specific heat is observed at T_N = 2.2 K, implying a phase transition. The magnetic susceptibility in a field applied along [100], which is a magnetically easy direction, remains almost the same value below T_N. The longitudinal elastic modulus, C₁₁, shows an obvious hardening at T_N, and TN decreases up to 0.4 T as the magnetic field applied along [100] increases, suggesting an antiferromagnetic ordering. In the magnetic field dependence of C₁₁ at 0.5 K, we discovered two abrupt softenings at 0.25 T and around 0.47 T, proposing that the antiferromagnetic phase boundary closes around 0.47 T in the field applied along [100]. Other phase boundary exists around 0.25 T in the ordered state