Magnetically ordered state and crystalline-electric-field effects in SmBe₁₃

The physical properties of single-crystalline SmBe₁₃ with a NaZn₁₃-type cubic structure have been studied by electrical resistivity (ρ), specific heat (C), and magnetization (M) measurements in magnetic fields of up to 9 T. The temperature (T) dependence of ρ shows normal metallic behavior without showing the Kondo −ln T behavior, suggesting the weak hybridization effect in this system. Analyses of the temperature dependence of C suggest that the Sm ions of this compound are trivalent and that the crystalline-electric-field (CEF) ground state is a Γ₈ quartet with a first-excited state of a Γ₇ doublet located at the energy scale of ~90 K. Mean-field calculations based on the suggested CEF level scheme can reasonably well reproduce the T dependence of magnetic susceptibility (χ) below ~70 K. These results in the paramagnetic state strongly indicate that the 4 f electrons are well localized with the Sm³⁺ configuration. At low temperatures, the 4 f electrons undergo a magnetic order at T_M ~ 8.3 K, where _χ (T) shows an antiferromagnetic-like cusp anomaly. From the positive Curie–Weiss temperature obtained from the mean-field calculations and from a constructed magnetic phase diagram with multiple regions, we discussed the magnetic structure of SmBe₁₃ below T_M, by comparing with other isostructural MBe₁₃ compounds showing helical-magnetic ordering.