Investigation of ESR on Fe Ions in Kondo Dielectric SmB6

Electron spin resonance (ESR) was studied in Kondo dielectric SmB6 doped with 1 at.% of Fe. The ESR measurements were performed on single crystal of SmB6 in the temperature range 10–300 K. We have observed two resonance lines with g-factors of 2.25 and 3.0 indicating the presence of iron in Fe0 and Fe2+ states. Ferromagnetic ordering of iron ions is observed below the Curie point at 100 K, which can be attributed to indirect exchange of impurity ions via polarization of the matrix (a mechanism similar to that found in PdFe alloys). However, the estimate of the intensity of this indirect exchange demonstrate nearly three orders of magnitude enhancement compared to its value in PdFe caused by extraordinary high density of states in a narrow f-band characteristic of material with the fluctuating valence.