High- Tc cuprates, iron pnictides, organic BEDT and TMTSF, alkali-doped C60, and heavy-fermion systems have superconducting states adjacent to competing states exhibiting static antiferromagnetic or spin density wave order. This feature has promoted pictures for their superconducting pairing mediated by spin fluctuations. Sr2RuO4 is another unconventional superconductor which almost certainly has a p-wave pairing. The absence of known signatures of static magnetism in the Sr-rich side of the (Ca, Sr) substitution space, however, has led to a prevailing view that the superconducting state in Sr2RuO4 emerges from a surrounding Fermi-liquid metallic state. Using muon spin relaxation and magnetic susceptibility measurements, we demonstrate here that (Sr,Ca)2RuO4 has a ground state with static magnetic order over nearly the entire range of (Ca, Sr) substitution, with spin-glass behaviour in Sr1.5Ca0.5RuO4 and Ca1.5Sr0.5RuO4. The resulting new magnetic phase diagram establishes the proximity of superconductivity in Sr2RuO4 to competing static magnetic order.
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This work has been supported by the US National Science Foundation (NSF) under the Materials World Network (MWN: DMR-0502706 and 0806846), the Partnership for International Research and Education (PIRE: OISE-0968226) and DMR-1105961 programs at Columbia, by the Canadian Natural Sciences and Engineering Research Council (NSERC) and the Canadian Institute for Advanced Research (CIFAR) at McMaster, and by Grants-in-Aid (No. 21684019) from the Japan Society for the Promotion of Science (JSPS) and (No. 19052003) for Scientific Research on Priority Areas (SRPA) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) at Kyoto and Tokyo Universities, and by MEXT-SRPA (No. 19052006) at Osaka University.
The authors declare no competing financial interests.
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Carlo, J., Goko, T., Gat-Malureanu, I. et al. New magnetic phase diagram of (Sr,Ca)2RuO4. Nature Mater 11, 323–328 (2012). https://doi.org/10.1038/nmat3236
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