ITINERANT-TO-LOCALIZED ELECTRON TRANSITION IN CARU1-XSRXO3 AND SRRU1-XPBXO3

SrRuO3 and CaRuO3 are perovskites with an orthorhombic distortion and are believed to have a narrow itinerant band. SrRuO3 is the only known ferromagnetic conductor in 4d transition-metal oxides, while CaRuO3 i s a paramagnetic conductor. Substituting Pb and Sn for Ru in SrRuO3 an d CaRuO3, respectively, preserves the crystal structure, while removin g electrons from the 4d band, resulting in an itinerant-to-localized e lectron transition and also substantially altering the magnetic coupli ng, giving rise to a new magnetically ordered phase. In particular, it appears that the paramagnetic CaRuO3 is on the verge of magnetic orde ring and readily evolves into a magnetically ordered phase when slight ly doped with Sn (4-10%). Such an ordered phase is not stable and disa ppears when Sn concentration is higher than 10%. On the other hand, th e Curie temperature (T-C = 165 K) of SrRuO3 seems to be sensitive to P b doping, and increases to 210 K when the Pb concentration in the comp ound is higher than 30%. For both SrRuO3 the transition to the magneti c state is accompanied by an itinerant-to-localized electron transitio n due to the 4d-electron depletion. These results are based on measure ments of magnetic susceptibility and electrical resistivity. This stud y reveals striking observations which underscore the importance of the interplay between the conduction band and (anti)ferromagnetism.