An external magnetic field, H, applied parallel to a quasi two-dimensional
system modifies quantitatively and qualitatively the density of states. Using a
self-consistent numerical approach, we study how this affects the entropy, S,
the free energy, F, and the magnetization, M, for different sheet carrier
concentrations, Nsβ. As a prototype system we employ III-V double quantum
wells. We find that although M is mainly in the opposite direction of H,
the system is not linear. Surprisingly βM/βH swings between
negative and positive values, i.e., we predict an entirely orbital diamagnetic
to paramagnetic fluctuation. This phenomenon is important compared to the ideal
de Haas-van Alphen effect i.e. the corresponding phenomenon under perpendicular
magnetic field.Comment: 4 pages, 6 figure