Electronic, magnetic, and transport properties of the isotypic aluminides SmT₂Al₁₀ (T = Fe, Ru).

We report the results of a comprehensive physical and magnetic property study of the new isotypic aluminides SmT₂Al₁₀ (T = Fe, Ru). These two compounds are members of a rare-earth based system which has become an exemplary case study of the interplay of magnetism and correlated electron phenomena. SmFe₂Al₁₀ and SmRu₂Al₁₀ are found to order in a putative antiferromagnetic spin arrangement at T(N) = 14.5 K and 12.5 K, respectively. Moreover, SmRu₂Al₁₀ shows a further phase transition at T(SR) = 5 K which is likely due to spin reorientation. The susceptibility of SmFe₂Al₁₀ points to a valence instability of the Sm ionic state at intermediate temperatures well above T(N). Electronic and thermal transport confirm that SmFe₂Al₁₀ undergoes an antiferromagnetic superzone gap formation below T(N), whereas SmRu₂Al₁₀ suffers a lattice anomaly driven magnetoelastic coupling at T(N). Below T(N), the physical properties of SmT₂Al₁₀ (T = Fe, Ru) are governed by magnons with an antiferromagnetic spin-wave spectrum that reveals spin-gap opening. Our findings in this work have exposed a new anomalous correlated compound in the RT₂Al₁₀ series. SmFe₂Al₁₀ has a magnetic ordered ground state in spite of an unstable valence at higher temperature. This is comparable with CeRu₂Al₁₀, which is a unique and controversial Kondo insulator that orders antiferromagnetic at T(N) = 27 K. Among the series of rare-earth RT₂Al₁₀ compounds, the presented Sm compounds are two new members with anomalously high magnetic ordering temperatures, and it is envisaged that together with the two very well studied compounds CeRu₂Al₁₀ and CeOs₂Al₁₀ our presented studies will enable a broader approach towards understanding the fascinating properties of this materials class.