High spin polarization in the ferromagnetic filled skutterudites KFe4Sb12 and NaFe4Sb12 -: art. no. 180407

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 P-t of 67% and 60% for the K and Na compound, respectively, is inferred, which establishes these materials as a class of highly spin-polarized ferromagnets. The results are in accord with band structure calculations within the local spin density approximation that predict nearly 100% spin polarization in the density of states. We discuss the impact of calculated Fermi velocities and spin fluctuations on P-t.