Lattice effects on the physical properties of half-doped perovskite ruthenates.

We investigate the unusual phase transitions in SrRuO3 and Sr0.5Ca0.5Ru1-xCrxO3 (x=0,0.05
and 0.1) employing x-ray diffraction, resistivity, magnetic studies and x-ray photoemission spectroscopy. Our results show the compounds undergo a crossover from itinerant ferromagnetism to
localized ferromagnetism. The combined studies suggest Ru and Cr be in the 4+ valence state. A
Griffith phase and an enhancement in Curie temperature (Tc) from 38 K to 107 K are observed with
Cr doping. A shift in the chemical potential towards the valence band is observed with Cr doping.
In the metallic samples, interestingly, a direct link between the resistivity and orthorhombic strain
is observed. We also observe a connection between orthorhombic strain and Tc in all the
samples. Detailed studies in this direction will be helpful to choose suitable substrate
materials for thin-film/device fabrication and hence manoeuvre its properties. In the
non-metallic samples, the resistivity is mainly governed due to disorder, electron-electron correlation effects and a reduction in the number of electrons at the Fermi level. The value of
the resistivity for the 5% Cr doped sample suggests semi-metallic behaviour. Understanding its
nature in detail using electron spectroscopic techniques could unravel the possibility of its utility
in high-mobility transistors at room temperature and its combined property with ferromagnetism
will be helpful in making spintronic devices.