TlFe4Sb12:: Weak itinerant ferromagnetic analogue to alkali-metal iron-antimony skutterudites

Structural, thermal, electronic, and electrical transport properties as well as high-field Fe-57 Mossbauer investigations are reported for thallium iron antimonide TlFe4Sb12, in which thallium attains the formal charge of +1. Similar to the isostructural NaFe4Sb12 and KFe4Sb12 homologues, the Tl-filled skutterudite is an itinerant ferromagnet with small ordered moment below T-C=80 K. The electronic structure calculated by density functional methods exhibits a band-ferromagnetic ground state and nearly half-metallic properties. The specific heat is dominated by a low-lying mode due to vibrations of the Tl cation in the cavity of the [Fe4Sb12] polyanionic host. Electrical resistivity displays a characteristic hump and a sharp anomaly at T-C. These features and the large magnetoresistance at low temperatures can be explained by a strong compensation of hole and electron carriers in the band structure. Temperature-dependent Fe-57 Mossbauer spectroscopy confirms the magnetic character.