  We demonstrate that SrRuO3 and CaRuO3 thin films undergo a room temperature
structural phase transition driven by the substrate imposed epitaxial biaxial
strain. As tensile strain increases, ARuO3 (A=Ca, Sr) films transform from the
orthorhombic phase which is usually observed in bulk SrRuO3 and CaRuO3 at room
temperature, into a tetragonal phase which in bulk samples is only stable at
higher temperatures. More importantly, we show that the observed phenomenon
strongly affects the electronic and magnetic properties of ARuO3 thin films
that are grown on different single crystal substrates which in turn offers the
possibility to tune these properties.
