Ferromagnetism in quark matter

Abstract

We investigate the magnetic property of the cold quark matter employing the magnetic moment $\vecμ&#39;$ as the order parameter. Through analysis of the effective potential $V (\vecμ^{&#39; 2})$, we find that, at relatively high densities $ρ> ρ_c$, the quark matter is in the normal phase. At $ρ= ρ_c$, the magnetic phase transition takes place and, in the low-density region $ρ< ρ_c$, the quark matter is in the ferromagnetic phase. For up, down and strange quarks, $ρ_c = 1.62 ρ_0$, $1.47 ρ_0$ and $2.20 ρ_0$ ($ρ_0$ the nuclear density), respectively. We also find that the leptons ($e$ and $μ$) inside the quark matter are in the normal phase.