  We show how the orbital magnetization of an interacting disordered diffusive
electron gas can be simply related to the magnetization of the non-interacting
system having the same geometry. This result is applied to the persistent
current of a mesoscopic ring and to the relation between Landau diamagnetism
and the interaction correction to the magnetization of diffusive systems. The
field dependence of this interaction contribution can be deduced directly from
the de Haas-van Alphen oscillations of the free electron gas. Known results for
the free orbital magnetism of finite systems can be used to derive the
interaction contribution in the diffusive regime in various geometries.
