  We present scanning SQUID microscopy data on the superconductors Sr2RuO4 (Tc
= 1.5 K) and PrOs$_4$Sb$_{12}$ (Tc = 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 Sr$_2$RuO$_4$ nor PrOs$_4$Sb$_{12}$ do we observe
spontaneous superconductivity-related magnetization. In Sr$_2$RuO$_4$, many
experimental results have been interpreted on the basis of a $px \pm ipy$
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.
