  Solid state wafers are indispensable components in material science as
substrates for epitaxial homo- or hetero-structures or carriers for
two-dimensional materials. However, a reliable determination of magnetic
properties of nanomaterials in volume magnetometry is frequently affected by
unexpectedly rich magnetism of these substrates, including significant magnetic
anisotropy. Here, we describe a simplified experimental routine of magnetic
anisotropy assessment, which we exemplify and validate for epi-ready sapphire
wafers from various sources. Both the strength and the sign of magnetic
anisotropy is obtained from carefully designed temperature dependent
measurements, which mitigate all known pitfalls of volume SQUID magnetometry
and are substantially faster than traditional approaches. Our measurements
indicate that in all the samples two types of net paramagnetic contributions
coexists with diamagnetism. The first one can be as strong as 10% of the base
diamagnetism of sapphire [-3.7(1) x 10-7 emu/gOe], and, when exceeds 2% mark,
it exhibits pronounced magnetic anisotropy with the easy axis oriented
perpendicularly to the face of c-plane wafers. The other is much weaker but
exhibit ferromagnetic-like appearance. These findings form an important message
that non-standard magnetism of common substrates can significantly influence
the results of precise magnetometry of nanoscale materials and its existence
must be taken for granted by both industry and academia.
