Weak itinerant ferromagnetism and electronic and crystal structures of alkali-metal iron antimonides: NaFe4Sb12and

Abstract

The synthesis, chemical, structural, and magnetic properties of alkali-metal compounds with filledskutterudite structure, NaFe 4 Sb 12 and KFe 4 Sb 12 , are described. X-ray and neutron diffraction and elemental analysis established the crystal structure without defects and disorder on the cation site. The temperature and pressure dependence of the cubic unit cell of NaFe 4 Sb 12 and the displacement parameter of Na are investigated. The electronic structure is calculated by density functional methods (LMTO, FPLO). Quantum chemical calculations (electron localization function) reveal the covalent character of both Fe-Sb and Sb-Sb interactions. Electronic structure calculations within the local density approximation exhibit a band ferromagnetic ground state and predict a half-metallic behavior. In contrast to isostructural alkaline-earth compounds (CaFe 4 Sb 12 and BaFe 4 Sb 12 ), the alkali-metal skutterudites are itinerant electron ferromagnets with small magnetic moments (Ϸ0.25 B / Fe atom) and T C Ϸ 85 K. Yet the paramagnetic moments of all four compounds are between 1.5 B and 1.7 B per Fe atom, indicating similar Stoner factors. Temperature-dependent 57 Fe and 121 Sb Mössbauer spectroscopies confirm the ferromagnetic state in the sodium compound with very small hyperfine fields at the iron and antimony sites.

Iron-based heavy quasiparticles inSrFe4Sb12: An infrared spectroscopic study

“…Alkaline-earth-filled iron-antimony skutterudites (A 2+ Fe 4 Sb 12 ), including the SrFe 4 Sb 12 system studied in this paper, are almost ferromagnetic systems with a paramagnetic Curie temperature (T C ) of 53 K 7,8,9 . Alkali-filled iron-antimony skutterudites (A + Fe 4 Sb 12 ) possess an itinerant ferromagnetic character with a T C = 80 K 10,11,12 . Both systems can be fundamentally explained by the self-consistent renormalization (SCR) theory 13 .…”

High-temperature electrical and thermal transport properties of fully filled skutterudites RFe4Sb12 (R = Ca, Sr, Ba, La, Ce, Pr, Nd, Eu, and Yb)

“…Therefore, systematic and deep understanding on the thermoelectric properties of single element filled skutterudites is necessary and urgent for the design and optimization in p-type double and multiple-filled skutterudites. 3,4,6,8,10,[26][27][28][29][30][31][32][33][34][35][36][37][38] However, the thermoelectric properties were only studied in a few RFe 4 Sb 12 compounds experimentally. 3,6,10,22,30,31 Furthermore, high temperature thermoelectric properties, which are crucial to the thermoelectric power generator, have been rarely reported in RFe 4 Sb 12 .…”

A large family of filled skutterudites stabilized by electron count

“…Because they make very good thermoelectrics 21,22,47 , host unusual metalinsulator transitions [23][24][25] , can be rare-earth magnets, heavyfermion compounds [26][27][28][29][30] , non-Fermi liquids [31][32][33][34][35] , itinerant ferromagnets [36][37][38] and superconductors 27,[39][40][41][42][43][44][45][46] , and have been proposed as topological insulators 48 , filled skutterudites are a very important class of non-molecular solids. Because the electronic and magnetic properties of solids depend critically on the actual atoms making up the compounds in addition to the compound's electron count, expanding the filled skutterudites from primarily group 8 to group 9 metal-based compounds, as we have done in this study, affords the opportunity to observe many new physical properties.…”