Ferromagnetism in the Hexagonal Cage-like Compounds

We report the synthesis and characterization for two single crystalline lanthenide-host compound Sm$_{6}$T$_{4}$Al$_{43}$ (T = Mo and W), that form in the hexagonal Ho$_{6}$Mo$_{4}$Al$_{43}$ prototype. The Sm ions reside within T/Al cages in which the Sm-Sm nearest neighbors form dimers between adjacent T/Al cages. In which T/Al networks provide a similar environments to those of other cage-like materials (filled skutterudites). Magnetic susceptibility measurements show that both compounds exhibit low anisotropy at high temp with a Curie-Weiss temperature that is positive indicating ferromagnetic ordering. The Modified Curie-Weiss behavior for the fits of the data yield a reduced effective magnetic moment below the expected tetravalent Sm ion (Sm$^{3+}$), which is typical behavior for Sm compounds exhibiting van Vleck paramagnetism. At low temperatures, both compounds demonstrate magnetic anisotropy, with the crystallographic c axis being the easy axis. Specific heat measurements for the Sm$_{6}$T$_{4}$Al$_{43}$ reveal an enhanced electronic Sommerfeld coefficient that is consistent with a moderately enhanced charge carrier effective mass. The electrical resistivity decreases with decreasing temperature, suggesting that it dominated by f-electronic hybridization effects and with a slight indication for Kondo-like behavior.