Abstract
It is known that the electro-transport and magnetism of perovskite alkaline-earth ruthenate oxides are sensitive to the lattice distortion associated with the A-site cation size. Orthorhombic CaRuO3 and cubic BaRuO3 exhibit distinctly different electro-transport and magnetic properties from orthorhombic SrRuO3. It has been suggested that SrRuO3 can be robust against some intrinsic/external perturbations but fragile against some others in terms of electro-transport and magnetism, and it is our motivation to explore such stability against the local site cation disorder. In this work, we prepare a set of SrRuO3-based samples with identical averaged A-site size but different A-site cation disorder (size mismatch) by Ca and Ba co-substitution of Sr. It is revealed that the electro-transport and magnetism of SrRuO3 demonstrate relatively high stability against this A-site cation disorder, characterized by the relatively invariable electrical and magnetic properties in comparison with those of SrRuO3 itself. A simple electro-transport network model is proposed to explain quantitatively the measured behaviors. The present work suggests that SrRuO3 as an itinerant electron ferromagnetic metal possesses relatively high robustness against local lattice distortion and cation occupation disorder.
Highlights
For ABO3 perovskites, the ionic size mismatch between the A and B sites is the origin for lattice symmetry variation and structural distortions realized by oxygen octahedra rotation and/or tilting, which are often discussed within the framework of structural tolerance factor[21,22]
It should be noted that a change of RA for ~7% regarding o-SRO and o-CRO is not a small quantity, leading to remarkable differences in lattice parameters and distortion between them, as summarized in Table 1 taken from our data and literature[14,33]
A comparison between o-SRO and o-CRO is far from sufficient to conclude whether the electronic structure and magnetism of ARuO3 are robust or fragile against structural variations
Summary
For ABO3 perovskites, the ionic size mismatch between the A and B sites is the origin for lattice symmetry variation and structural distortions realized by oxygen octahedra rotation and/or tilting, which are often discussed within the framework of structural tolerance factor[21,22]. A more distorted perovskite would give rise to a small W which favors an antiferromagnetism and probably bad electron itinerancy large ρ This hypothesis does not apply to the magnetism of ARuO3, noting that it is o-SRO instead of c-BRO to have the highest Tc (strongest ferromagnetism)[32,47]. The causes for ferromagnetism disappearance in o-CRO and reduction in c-BRO with respect to o-SRO, are under hot debate[8,14,15,16,30], which hints some questions on the consensus regarding the evolution of electronic structure and magnetism of ARuO3 with intrinsic or external perturbations. The latter ingredient seems to be dominant for c-BRO, explaining the low Tc and large ρ of c-BRO with respect to o-SRO9,32
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