Is a Field-Induced Ferromagnetic Phase Transition in the Magnetar Core Actually Possible?

TL;DR

This paper investigates whether a ferromagnetic phase transition can occur in magnetar cores, concluding that strong magnetic fields induce instabilities that prevent full spin polarization, allowing only moderate polarization states.

Contribution

It demonstrates that longitudinal instabilities in dense neutron matter under extreme magnetic fields inhibit complete spin polarization, challenging previous assumptions about ferromagnetic transitions in magnetar cores.

Findings

Longitudinal instability prevents full spin polarization.

Only moderate spin polarization states are possible.

Strong magnetic fields induce instabilities in neutron matter.

Abstract

Spin polarized states in dense neutron matter with BSk20 Skyrme force are considered in magnetic fields up to $10^{20}$ G. It is shown that the appearance of the longitudinal instability in a strong magnetic field prevents the formation of a fully spin polarized state in neutron matter, and only the states with moderate spin polarization can be developed.