The nature of 4f electron magnetism in the diluted ferromagnetic Kondo lattice, CeIr2B2.

We report on the physical properties of the series Ce(1-x)La(x)Ir(2)B(2) (x = 0-0.9), obtained by means of magnetization, heat capacity and electrical resistivity measurements as a function of temperature (down to 0.7 K for the latter two measurements). The Curie temperature of CeIr(2)B(2) (~5 K) is lowered due to La substitution, as expected. However, no quantum critical point or 'non-Fermi liquid' behavior was observed even in the dilute limit of x = 0.9. Interestingly, ferromagnetic ordering persists even for Ce(0.1)La(0.9)Ir(2)B(2), below 0.8 K. Among the Ce systems, CeIr(2)B(2) is one of the compounds in which direct 4f-4f interaction does not appear to play any role in the magnetism, which is controlled by the indirect exchange interaction alone. In this compound, the Kondo effect persists in the ferromagnetic ordered state, as inferred from the entropy data.