Dependence of magnetism on GdFeO₃ distortion in the t_2g system ARuO₃(A = Sr, Ca)

Abstract

We have examined the stability of the ferromagnetic (FM) state in CaRuO₃ and SrRuO₃ as a function of the GdFeO₃ distortion. Model calculations predict the dependence of the FM transition temperature (T_c) on the rotation angle θ to vary as cos²(2θ) 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 CaRuO₃, a larger deviation of the Ru-O-Ru angle from 180∘ in CaRuO₃ as compared to SrRuO3 should result in a more reduced bandwidth, thereby making the former more correlated. The absence of long-range magnetic order in the more correlated CaRuO₃ is traced to the strong collapse of various exchange interaction strengths that arises primarily from the volume reduction and increased distortion of the RuO₆ octahedra network that accompanies the presence of a smaller ion at the A site.