Itinerant to localized electron transition in ferromagnetic (Ca,Sr)(1-x)NaxRuO3

SrRuO3 is an itinerant ferromagnet with T-C=165 K and CaRuO3 is a metallic paramagnet down to at least 30 mK. These materials are known to be narrow d -band metals, the physical properties of which are highly sensitive to smal l perturbations such as chemical doping. In this article, we report results of resistivity, specific heat, and magnetic susceptibility measurements on Na doped SrRuO3 and CaRuO3. Resistivity measurements show a change from me tallic to nonmetallic behavior for Na concentration of 12% with the ferroma gnetic ordering temperature depressed in Sr1-xNaxRuO3. The nonmetallic beha vior in the x=0.12 sample is supported by specific heat measurements which are suggestive of a partial opening of an energy gap and brings into questi on the role of itineracy in the magnetic ground state. Ca1-xNaxRuO3, with x =0.00, 0.05, and 0.09, remains metallic and shows no evidence of long range magnetic order for all x. (C) 1999 American Institute of Physics. [S0021-8 979(99)73208-1].