Magnetization of a neutron plasma with Skyrme and Gogny forces in the presence of a strong magnetic field

Some thermodynamical magnitudes of interest in a pure neutron plasma are studied within the framework of the nonrelativistic Hartree-Fock approximation at finite density and temperature. We use Skyrme and Gogny forces to describe such a neutron plasma and study the main differences that arise in these two effective parametrizations of the nuclear interaction when a strong magnetic field induces a permanent magnetization in the gas. The existence of a nonzero permanent spin polarization in a neutron plasma is explored in the density-temperature parameter space. We find that for moderate temperatures and in the low-density range up to densities approximate to 0.5 rho(0) both parametrizations predict that as density decreases an increasingly strong magnetization is allowed. In the range 0.5 rho(0)less than or similar to rho less than or similar to 3 rho(0) there is an approximately constant polarization that can be as big as approximate to 12% for the maximum allowed interior magnetic field B approximate to 10(18) G. For higher densities there is a dramatic difference in the polarization trend followed by Skyrme an Gogny forces. Although the former predict a ferromagnetic phase transition, the Gogny forces prevent it keeping the magnetization below 5%.