  SrTiO3 plays a central role in oxide electronics. It is the substrate of
choice for functional oxide heterostructures based on perovskite-structure
thin-film stacks, and its surface or interface with a polar oxide such as
LaAlO3 can become a two-dimensional conductor because of electronic
reconstruction or the presence of oxygen defects. Inconsistent reports of
magnetic order in SrTiO3 abound in the literature. Here we report a systematic
experimental study aimed at establishing how and when SrTiO3 can develop a
magnetic moment at room temperature. Polished 100, 110 or 111 crystal slices
from four different suppliers are characterized before and after vacuum
annealing at 750 {\deg}C, both in single-crystal and powdered form. Impurity
content is analysed at the surface and in the bulk. Besides the underlying
intrinsic diamagnetism of SrTiO3, magnetic signals are of three types-a Curie
law susceptibility due to dilute magnetic impurities at the ppm level, a
hysteretic, temperature-dependent ferromagnetic impurity contribution, and a
practically-anhysteretic, defect-related temperature-independent component that
saturates in about 200 mT. The latter component is intrinsic. It is often the
largest, reaching 10 Bohr magnetons per nm2 of surface area or more and
dominating the magnetic response in low fields at room temperature. It is
associated with defects near the surface, and can be destroyed by treatment
with Tiron (C6H4Na2O8S2), an electron donor molecule that forms a strong
complex with titanium at the surface. The origin of this unusual
high-temperature ferromagnetic-like response is discussed.
