Competition Between Antiferromagnetism and Ferromagnetism in Sr$_{2}$RuO$_{4}$ Probed by Mn and Co Doping

Spin-triplet superconductivity in Sr$_{2}$RuO$_{4}$ has attracted enormous interest. Like other unconventional superconductors, superconductivity in Sr$_{2}$RuO$_{4}$ is in close proximity to magnetic instability. Undoped Sr$_{2}$RuO$_{4}$ exhibits incommensurate antiferromagnetic (AFM) fluctuations, which can evolve into static, short-range AFM order via Ti doping. Moreover, weak ferromagnetic (FM) coupling in Sr$_{2}$RuO$_{4}$ has also been suggested by NMR/neutron scattering experiments and studies on Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ and Sr$_{2-y}$La$_{y}$RuO$_{4}$. In this talk, we will report bulk static, short-range FM order in Sr$_{2}$RuO$_{4}$ triggered by \textless 2{\%} Co doping, showing superconductivity in Sr$_{2}$RuO$_{4}$ is much closer to FM instability than previously reported in Ca$_{2-x}$Sr$_{x}$RuO$_{4}$. We also find Mn doping can effectively establish incommensurate AFM order, with $T_{N}$ $\sim$ 50 K for 3{\%} Mn doping. These new results highlight the important role of competing magnetic fluctuations in determining superconducting properties of Sr$_{2}$RuO$_{4}$[1]. \\[4pt] [1] Ortmann et al., Scientific Report 3, 2950 (2013).