Structural modulation driven Curie temperature enhancement in Cr-doped SrRuO3

A strongly correlated system with competing ground states is often poised close to the quantum critical point. External perturbations such as pressure, strain, electric field, and chemical doping can stabilize its ground state with exotic physical properties. Cr-doping is the lone exception, which enhances the Curie temperature in one such correlated system, ${\mathrm{SrRuO}}_{3}$. To find the origin of ${T}_{C}$ enhancement, we investigate the temperature-dependent structure, spectroscopic, magnetic, and magnetotransport properties in ${\mathrm{SrRu}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{3}$. Cr-doping squeezes the unit cell volume, which effectively enhances the stretching octahedral distortion nearly five times more than pure ${\mathrm{SrRuO}}_{3}$. The Curie temperature increment of $\ensuremath{\sim}22$ K for $x=0.15$ is found to be intertwined with the structural modulation. Temperature-dependent neutron diffraction analysis indicates that the unit cell volume minima coincide exactly with the enhanced ferromagnetic ordering ($\ensuremath{\sim}190$ K). Further analysis reveals that the effect of Cr-doping not only freezes the octahedral tilt below 100 K but also suppresses the complex magnetism responsible for exchange bias and the topological Hall effect in ${\mathrm{SrRuO}}_{3}$. The spectroscopic measurements find a reduction of itinerancy of $d$-electrons with Cr-doping. The magnetotransport measurements portray an evolution from itinerant to localized ferromagnetism.