  The problem of two electrons in a square billiard interacting via a
finite-range repulsive Yukawa potential and subjected to a constant magnetic
field is considered. We compute the energy spectrum for both singlet and
triplet states, and for all symmetry classes, as a function of the strength and
range of the interaction and of the magnetic field. We show that the
short-range nature of the potential suppresses the formation of ``Wigner
molecule'' states for the ground state, even in the strong interaction limit.
The magnetic susceptibility $\chi(B)$ shows low-temperature paramagnetic peaks
due to exchange induced singlet-triplet oscillations. The position, number and
intensity of these peaks depend on the range and strength of the interaction.
The contribution of the interaction to the susceptibility displays paramagnetic
and diamagnetic phases as a function of $T$.
