Limits on superconductivity-related magnetization in Sr₂RuO₄ and PrOs₄Sb₁₂ from scanning SQUID microscopy

We present scanning superconducting quantum interference device microscopy data on the superconductors Sr₂RuO₄ (T_c=1.5 K) and PrOs₄Sb₁₂ (T_c=1.8 K). In both of these materials, superconductivity-related time-reversal symmetry-breaking fields have been observed by muon spin rotation; our aim was to visualize the structure of these fields. However, in neither Sr₂RuO₄ nor PrOs₄Sb₁₂ do we observe spontaneous superconductivity-related magnetization. In Sr₂RuO₄, many experimental results have been interpreted on the basis of a p_x±ip_y superconducting order parameter. This order parameter is expected to give spontaneous magnetic induction at sample edges and order parameter domain walls. Supposing large domains, our data restrict domain wall and edge fields to no more than ∼0.1% and ∼0.2% of the expected magnitude, respectively. Alternatively, if the magnetization is of the expected order, the typical domain size is limited to ∼30 nm for random domains or ∼500 nm for periodic domains.