Ferromagnetism of electrons in solid quark-cluster stars

In this paper we are trying to solve the problem of the origin of strong magnetic fields in the framework of solid quark-cluster stars. We propose that, under the Coulomb repulsion, the electrons inside the stars could spontaneously magnetized and become ferromagnetic, and hence would contribute non-zero net magnetic momentum to the whole star. The leading order approximation in our simple model shows that the magnetism of solid quark-cluster matter could be possible. For most cases in solid quark-cluster stars, the amount of net magnetic momentum, could be significant, and the net magnetic moments of electron system in solid quark-cluster stars could be large enough to induce the observed magnetic fields for pulsars with $B\sim 10^{11}$ to $\sim 10^{13}$ Gauss. This mechanism of generating magnetic field is not valid for so-called magnetars.