Neutron spin quantum plasmas – Ferromagnetism as a relaxed state

It is shown that a ferromagnetic “minimum energy relaxed state” is accessible to a neutron fluid. We model the neutron fluid as a spin quantum plasma where the electromagnetic interaction is trough the magnetic moment of the neutron. The neutron ferromagnetism results from the macroscopic spin alignment that occurs due to a profound interplay between the classical and spin quantum vorticities carried by the charge-less neutron fluid. The simplest manifestation of a neutron superfluidity comes about by an exact cancellation of the quantum and classical vorticities to create a helicity free system. •We model a neutron fluid as a spin quantum plasma, where the electromagnetic interaction is through the neutron magnetic moment.•The relaxed states are found using the recently introduced quantum vorticity and the generalized vorticity for quantum plasmas.•A solution provides a macroscopic aligned magnetic field which origin is the spin of the neutron plasma.