Kondo-hole conduction and magnetism of the lightly La-doped Kondo insulator CeRhSb

The effect of La doping of CeRhSb has been studied with the help of electrical resistivity, magnetic susceptibility, and specific-heat measurements for the system of Ce(1-x)La(x)RhSb with x<0.2. Particular emphasis is put on the extreme low-doping regime, x similar to 0.02. Namely, we show that the resistivity increase induced by appearance of the Kondo gap for x=0 is transformed into that caused by itinerant f holes and appears already for x=0.02. The studies indicate also that a spin-glasslike behavior, intermixed with a ferromagnetic component in these materials, is induced by statistical distribution of La ions. Our study also shows that the Kondo gap in CeRhSb is very sensitive to the magnitude of hybridization V between the 4f-electron and the conduction-electron states. The results for the system Ce(1-x)La(x)RhSb are interpreted in terms of (narrow) Kondo-hole band, located near at the Fermi level, that gives rise to an abrupt transition from the Kondo-insulator regime to a metallic state via an intermediate step (at very low doping) involving formation of the ferromagnetic clusters containing a Kondo hole (i.e., magnetic polarons). Finally, a comparison between Ce(1-x)La(x)RhSb with Ce(1-x)La(x)NiSn systems is carried out to contrast the concept of the polarons in Ce(1-x)La(x)RhSb with their absence in the latter system due to the dominant antiferromagnetic interaction among the 4f(1) spins.