[en] A comparative magnetic resonance study on correlated semiconductors is presented. Nuclear spin-lattice relaxation measurements provide an excellent method to gain local information about the gap formation in this new class of materials. In contrast to U2Ru2Sn (Δ/k_B ∼ 230 K) in CeRu₄Sn₆ the gap is slightly reduced (Δ/k_B ∼ 200 K) and correlations form out of a residual density of states in the gap. For FeSb₂ there is revived interest after classifying this system as the second Fe containing Kondo insulator beside FeSi. Surprisingly, FeSb₂ shows a colossal Seebeck coefficient at low temperatures. Using ^121,123Sb nuclei as a local probe, our NMR/NQR investigations strongly support the gap scenario. The spin-lattice relaxation rate ¹²³(1/T₁) in the entire investigated temperature range 2-200 K is perfectly fitted with rectangle DOS model with narrow impurity in-gap band. These in-gap states might originate the high thermopower observed. The obtained gap value is (Δ/k_B ∼ 473 K).

[en] We have shown the effect of fast neutron irradiation on the magnetic phase transition and magnetocaloric effect (MCE) in a doped Ce(Fe_0.96Ru_0.04)₂, intermettalic. We show that this leads to suppression of MCE and a to a disordered ferromagnetic phase.