  Analytical calculations based on a Landau Level (LL) picture are reported for
an interface (with a finite-width Quantum Well (QW)) and for a fully
three-dimensional charged quantum electronic system in an external magnetic
field. They lead to a sequence of previously unnoticed singular features in
global magnetization and magnetic susceptibility that lead to nontrivial
corrections to the standard de Haas - van Alphen periods. Additional features
due to Zeeman splitting are also reported (such as new energy minima that
originate from the interplay of QW, Zeeman and LL Physics) that are possibly
useful for the design of quantum devices. A corresponding calculation in a
Composite Fermion picture leads to new predictions on magnetic response
properties of a fully-interacting electron liquid in a finite-width interface.
