Substitution at the Ru site in the itinerant ferromagnet SrRuO3

The doping of SrRuO3 at the Ru sites with various cations was investigated, controlling the oxygen composition in sealed tubes (STs). For these ST samples SrRu1-xMxO3, it is shown that doping with cations containing e(g) electrons, M = Zn2+, Ni2+, Co2+, Mn3+, decreases T-C significantly from 166 K for SrRuO3 down to 105 K, whereas in contrast, doping with Cr3+ which contains only t(2g) electrons increases T-C up to 188 K. All these samples exhibit negative magnetoresistance, showing a maximum effect close to T-C. By synthesizing the samples in air, it is shown that the resistivity of these oxides is significantly modified, showing an upturn at low temperature and a disappearance of the metal to metal transition, whereas the magnetic behaviour is practically unchanged. This modification of the transport properties is believed to be due to a variation of the oxygen stoichiometry at the grain boundary.