  We study the phase diagram of the Kondo-lattice model with nearest-neighbor
hopping in the square lattice by means of the variational Monte Carlo
technique. Specifically, we analyze a wide class of variational wave functions
that allow magnetic and superconducting order parameters, so to assess the
possibility that superconductivity might emerge close to the magnetic
instability, as often observed in heavy fermion systems. Indeed, we do find
evidence of d-wave superconductivity in the paramagnetic sector, i.e., when
magnetic order is not allowed in the variational wave function. However, when
magnetism is allowed, it completely covers the superconducting region, which
thus disappears from the phase diagram.
