  We explore a wide range of fundamental magnetic phenomena by measuring the
dephasing of matter-wave interference fringes upon application of a variable
magnetic gradient. The versatility of our interferometric Stern-Gerlach
technique enables us to study alkali atoms, organic radicals and fullerenes in
the same device, with magnetic moments ranging from a Bohr magneton to less
than a nuclear magneton. We find evidence for magnetization of a supersonic
beam of organic radicals and, most notably, observe a strong magnetic response
of a thermal C$_{60}$ beam consistent with high-temperature atom-like
deflection of rotational magnetic moments.
