Effect of A-site disorder on the magnetic transition in doped Sr₂YRuO₆ double perovskites

We investigate the effects of A-site cation disorder on the magnetic transition in doped Sr₂YRuO₆ insulating double perovskites. Disorder is induced by partially substituting Sr for Ca, Ba and La. The relative concentration of the doping ions was carefully chosen in order to warrant a constant average ionic radius equal to the one found in Sr²⁺. The variance, σ² = <r_A ²> − <r_A>², where r_A is the ionic radius of each type of ion occupying the A-site, is the parameter used to quantify disorder. Unexpectedly, in spite of the fact that the magnetic ground state in Sr₂YRuO₆ is the result of a delicate balance between competitive ferro- and antiferromagnetic interactions with bound lengths and angles playing a relevant role, the magnetic transition temperature is virtually insensitive to disorder, in sharp contrast to the behavior observed for metallic perovskites. This result supports the idea that the leading mechanism suppressing the magnetic transition in Sr₂YRuO₆ is the deviation from planarity of the RuO₂ layers.