Effects of Ca2+ ion substitution on the structure and magnetism of SrRuO3: Elusive magnetism

Abstract

SrRuO3 is an orthogonally distorted perovskite (Pbnm) structure whose ferromagnetism is often viewed as an itinerant ferromagnet. Although SrRuO3 has been studied for more than half a century, its structure, magnetism and transport properties are still poorly understood. In this paper, the structure and magnetic evolution of SrRuO3 are discussed in depth through the substitution of Ca2+ for Sr2+ at A sites. The results show that as the Ca substitution increases, the lattice constant decreases, the orthogonal distortion becomes larger, and the saturation magnetization MS, Curie temperature TC and Weiss temperature θp decrease accordingly. Eventually, the ferromagnetic SrRuO3 changes to paramagnetic CaRuO3. The critical exponent β of samples with different substitution contents was obtained by fitting the experimental results, and the value for SrRuO3 (β = 0.55) was similar to that obtained by mean field theory. However, the value increases with the substitution x of Ca, which can't be explained by any scaling theory. The results show that the increase in the value of β is related to the magnetic disorder caused by different magnetic interactions. Analysis using the Rhodes-Wohlfarth criterion indicates that Sr1-xCaxRuO3 has both itinerant-electron and localized-electron magnetism, which is consistent with the theoretical predictions.