Magnetic and thermal properties of SmRh₂Zn₂₀ single crystal

The magnetization, magnetic susceptibility, and specific heat of the single crystalline sample SmRh₂Zn₂₀ were measured. The valence of Sm ions in SmRh₂Zn₂₀ was found to be trivalent. No evidence of valence fluctuations was detected. SmRh₂Zn₂₀ is an antiferromagnet with T_N = 2.46 K. The observed magnetic phase transition temperature in the C(T, H) curves showed that T_N splits into two in the external field H along the [001] and [101] directions. On the other hand, T_N in H along the [111] direction did not split, decreasing to 2.20 K at H = 7 T. At 2 K, the magnetization M₁₁₁ in H along the [111] direction increased linearly with increasing field, while M₀₀₁ and M₁₀₁ deviated upward slightly from the linear dependence. We analyzed the observed magnetic and thermal properties of SmRh₂Zn₂₀ taking into account the crystalline-electric-field effect, the Zeeman energy, and the exchange interaction. The theoretical calculation well reproduced the experimental χ (T), M(H), C(T, H), and T_N(H), suggesting that the energy scheme of Sm³⁺ is composed of the ground state Λ₇ and the excited state Λ₈ with an energy gap of 10.8 K. The sublattice magnetic moments are expected to be along the 〈111〉 direction below T_N at H = 0 T. Variations of the magnetic structures induced by the external magnetic fields in a narrow temperature region around T_N are inferred on the basis of theoretical calculations.