The spin-polarized ferromagnetic state of a cold Fermi gas is investigated for interacting and non-interacting charge-neutral and $\beta$-equilibrated gases. The standard minimal couplings between the magnetic field and the fermions' charges and magnetic dipole moments define the fermions' interaction with the magnetic field. Assuming a variable coupling strength between the magnetic field and the fermion (baryon) dipole moments, it is shown that a ferromagnetized state can be achieved that corresponds to a lower energy spin-polarized state with a magnetic field entirely due to the gas's magnetic response. We find that, depending on the density, a very large increase in the baryon dipole moments is needed to achieve this ferromagnetized state. While the required increase seems unlikely, the induced magnetic field is of the order $\sim10^{17}$ gauss. Furthermore, while externally magnetized Fermi gases have an anisotropic pressure, the pressure of the ferromagnetized gas is completely isotropic and the thermodynamically preferred magnetized state.

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冷费米气体的自旋极化铁磁态

研究了冷费米气体的自旋极化铁磁态，用于相互作用和非相互作用的电荷中性和 $\beta$ 平衡气体。磁场与费米子的电荷和磁偶极矩之间的标准最小耦合定义了费米子与磁场的相互作用。假设磁场和费米子（重子）偶极矩之间的耦合强度可变，表明可以实现铁磁化状态，该状态对应于具有完全由于气体磁响应的磁场的较低能量自旋极化状态。我们发现，根据密度，需要极大地增加重子偶极矩才能实现这种铁磁化状态。虽然所需的增加似乎不太可能，感应磁场的数量级为 $\sim10^{17}$ 高斯。此外，虽然外部磁化的费米气体具有各向异性压力，但铁磁化气体的压力是完全各向同性的，并且是热力学优选的磁化状态。