On the physical properties of Sr1-xNaxRuO3 (x=0-0.19)

The metallic ferromagnetic perovskite-type SrRuO3 (T-C similar to 160 K) belongs to the class of materials with strongly correlated electrons. Nonetheless a simple ferromagnetism associated with isotropic interactions of low spin Ru4+ ions local moments is far too simple to explain the complex interplay between charge carriers and magnetic interactions. In that sense the suppression of ferromagnetism in isoelectronic Sr1-xCaxRuO3 was tentatively associated to the increased lattice distortion influencing primarily the 4d Ru bandwidths and, hence, the itinerancy and respective populations of the spin-up and spin-down electrons. In order to probe the robustness of the metallic ferromagnetism against electron occupation of 4d Ru orbital we prepared and characterized polycrystalline Sr1-xNaxRuO3 (x = 0.0-0.19) ceramics. The substitution of Sr2+ by Na1+, leading to formally mixed valence Ru4+/Ru5+, induces the decrease of the Curie temperature and spin-wave stiffness, which was determined independently from magnetic and specific heat data. On the other hand the effective paramagnetic moment remains essentially unchanged. All compounds are metallic in a sense of electrical resistivity and thermopower temperature dependence; the low temperature upturn of the electrical resistivity was explained on a base of the weak localization. The metallic nature of the samples is corroborated by Pauli paramagnetism and high Sommerfeld coefficient gamma, extracted from the low temperature specific heat, which increases from 30.9 mJ mol(-1) K-2 (x = 0.0) to 43.0 mJ mol(-1) K-2 (x = 0.19). (C) 2010 Elsevier Masson SAS. All rights reserved.