Spin asymmetry originating from densities of states: Criterion for ferromagnetism, structures and magnetic properties of 3d metals from crystal field based DOSs
Band ferromagnetism theory, correct evaluation of electron energies in sub-bands.
•
A new criterion for ferromagnetism is derived, without the need to use Hubbard terms.
•
Explanation of low coercive fields in metals through electron density conservation.
•
Prediction of correct Curie temperatures for iron and cobalt.
•
Re-entrant ferromagnetism at high temperatures, as possible origin of geomagnetism.
Abstract
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.