Dependence of magnetism on GdFeO3distortion in thet2gsystemARuO3(A=Sr, Ca)

Abstract

We have examined the stability of the ferromagnetic (FM) state in CaRuO${}_{3}$ and SrRuO${}_{3}$ as a function of the GdFeO${}_{3}$ distortion. Model calculations predict the dependence of the FM transition temperature ($T$${}_{c}$) on the rotation angle $\ensuremath{\theta}$ to vary as cos${}^{2}(2\ensuremath{\theta})$ for ${e}_{g}$-electron systems. However, here, we find an initial increase and then the expected decrease. Furthermore, a much faster decrease is found than predicted for ${e}_{g}$-electron systems. Considering the specific case of CaRuO${}_{3}$, a larger deviation of the Ru-O-Ru angle from ${180}^{\ifmmode^\circ\else\textdegree\fi{}}$ in CaRuO${}_{3}$ as compared to SrRuO${}_{3}$ should result in a more reduced bandwidth, thereby making the former more correlated. The absence of long-range magnetic order in the more correlated CaRuO${}_{3}$ is traced to the strong collapse of various exchange interaction strengths that arises primarily from the volume reduction and increased distortion of the RuO${}_{6}$ octahedra network that accompanies the presence of a smaller ion at the A site.