TlFe$_{4}$Sb$_{12}$: Weak itinerant ferromagnetic analogue to alkali-metal iron-antimony skutterudites
A. Leithe-Jasper, W. Schnelle, H. Rosner, R. Cardoso-Gil, M. Baenitz, J. A. Mydosh, Yu. Grin, M. Reissner, and W. Steiner

Structural, thermal, electronic, and electrical transport properties as well as high-field $^{57}$Fe M\"ossbauer investigations are reported for the new compound TlFe$_4$Sb$_{12}$ in which thallium attains the formal valency of +1. Similar to the isostructural NaFe$_4$Sb$_{12}$ and KFe$_4$Sb$_{12}$ homologues the Tl-filled skutterudite is an itinerant ferromagnet with small ordered moment below $T_\mathrm{C}$ = 80\,K. The electronic structure calculated by density functional methods exhibits a band-ferromagnetic groundstate 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 [Fe$_4$Sb$_{12}$] polyanionic host. Electrical resistivity displays a characteristic hump and a sharp anomaly at $T_\mathrm{C}$. 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 $^{57}$Fe M\"ossbauer spectroscopy confirms the magnetic character.

© 2008 The American Physical Society.