  We consider the large-$U$ limit of the one-band Hubbard model at half-filling
on a non-bipartite two-dimensional lattice. An external magnetic field can
induce a three-spin chiral interaction at order $1 / U^2 ~$. We discuss
situations in which, at low temperatures, the chiral term may have a larger
effect than the Pauli coupling of electron spins to a magnetic field. We
present a model which explicitly demonstrates this. The ground state is a
singlet with a gap; hence the spin susceptibility is zero while the chiral
susceptibility is finite and paramagnetic.
