High spin polarization in the ferromagnetic filled skutterudites   KFe4Sb12 and NaFe4Sb12
  The spin polarization of ferromagnetic alkali-metal iron antimonides KFe4Sb12 and NaFe4Sb12 is studied by point-contact Andreev reflection using superconducting Nb and Pb tips. From these measurements an intrinsic transport spin polarization Pt of 67% and 60% for the K and Na compound, respectively, is inferred which establishes these materials as a new class of highly spin polarized ferromagnets. The results are in accord with band structure calculations within the local spin density approximation (LSDA) that predict nearly 100% spin polarization in the density of states. We discuss the impact of calculated Fermi velocities and spin fluctuations on Pt. 
Goutam Sheet, H. Rosner, S. Wirth, A. Leithe-Jasper, W. Schnelle, U.   Burkhardt, J. A. Mydosh, P. Raychaudhuri, and Yu. Grin