Electrical and magnetic properties of R₃Al₁₁ (R = La, Ce, Pr, and Nd)

High-quality single crystals of R₃Al₁₁ (R = La, Ce, Pr, and Nd) with the La₃Al₁₁-type orthorhombic crystal structure (space group Immm) have been grown by the Al-flux method. For Ce ₃Al₁₁, signatures for ferromagnetic and antiferromagnetic orderings at T_C = 6.3 K and T_N = 3.2 K, respectively, have been observed in the magnetic susceptibility, magnetization, specific heat, and electrical resistivity. An antiferromagnet Pr₃Al₁₁, on the other hand, exhibits two magnetic transitions at T_N1 = 12.6 K and T_N2 = 3.1 K. An antiferromagnet Nd₃Al₁₁ also exhibits multiple magnetic transitions at T_N1 = 13.2 K, T _N2 = 9.4 K, T_N3 = 2.9 K, and T_N4 = 1.77 K in zero magnetic field. The transition at T_N4 has a first-order character. The crystalline electric field (CEF) analysis of magnetic susceptibility, magnetization and specific heat data shows that the CEF splitting is larger for Ce₃Al₁₁ than for Pr ₃Al₁₁ and Nd₃Al₁₁. The CEF ground state of Pr₃Al₁₁ is a singlet. Magnetic order occurs in this compound owing to the exchange mixing of the CEF ground state and low-lying excited states. The ferromagnetic like component of the magnetization for H ∥ [010] is characteristic of R₃Al₁₁ (R = Ce, Pr, and Nd), which is most likely due to the Dzialoshinsky-Moriya interaction for two nonequivalent R atoms.