Hi,Is it fair to say that magnetism rises from the fact that there

[marie2010]

hi,
Is it fair to say that magnetism rises from the fact that there are more up than down electrons or they also have to be at the Fermi level? I am a little bit confused about this Fermi level thing. I heard people saying that up/down electrons difference must be at the fermi level.
Also, does it mean that an odd number of electrons will always give magnetism?
Can someone comment on this, please?
Thanks.

 

[abhi2005singh]

There should be an imbalance between the electrons with up and down spin. All the core levels are generally occupied, hence the imbalance is visible at the Fermi level. However, this may not be true in certain cases. For e.g. in transition metal compounds, if the partially filled d-levels of the transition metal lie below the Fermi level, then you may not see any exchange splitting at the Fermi level and the material can still be magnetic.

Odd no. of electrons may not always show magnetism, if by magnetism you mean ferromagnetism. Ferro- or antiferro-magnetism depends upon the exchange interaction among the localized magnetic moments. Lack of exchange interaction among the localized magnetic moments leads to the paramagnetic behavior.

 

[DrDu]

Also mind that magnetism is usually an effect due to strong electronic correlation. However, once electronic correlation is present, it may not even be possible to define the Fermi energy.

 

[marie2010]

Thank you all for replying. DrDu, would you please elaborate a bit more about the electronic correlation and the Fermi energy.

Also, could you please help me understand how localization or delocalization of electrons is related to magnetism. Can delocalized charge lead to magnetism?
Thank you.