Ferromagnetism in 3d metals is re-examined in a simple band model. It is shown that the molecular field model cannot account for the low values of coercive field in ferromagnetic pure metals, and that the standard Stoner theory of band ferromagnetism incorrectly evaluates the total electronic energy and cannot predict reasonable Curie temperatures. A simple band model for magnetism is formulated, yielding a criterion for ferromagnetism even in absence of a Hubbard term, involving only the density of states (DOS) at the Fermi level, its derivative and the filling of the 3d band. By introducing a double-peaked DOS, one may explain the occurrence of ferromagnetism in bcc Fe, hcp-fcc Co and fcc Ni, the stabilization of fcc-hcp or bcc structures across all 3d elements, the occurrence of antiferromagnetism in chromium, and derive reasonable Curie temperatures. ‘Re-entrant’ ferromagnetism is predicted at ultrahigh temperatures, suggesting an alternate origin for the geomagnetic field.

用简单的带模型重新检查3d金属中的铁磁性。结果表明，分子场模型不能解释铁磁性纯金属中矫顽场的低值，并且标准的斯通纳带铁磁性理论不正确地估计了总电子能量，并且无法预测合理的居里温度。建立了一个简单的磁性带模型，即使没有Hubbard项，也能得出铁磁性的准则，该模型仅涉及费米能级的态密度（DOS），其导数和3 d带的填充。通过引入双峰DOS，可以解释bcc Fe，hcp - fcc Co和fcc中铁磁性的发生Ni，所有3 d元素中fcc - hcp或bcc结构的稳定化，铬中反铁磁性的发生，并推导出合理的居里温度。预计在超高温下会出现“折返”铁磁性，这暗示了地磁场的另一种起源。