Magnetic Moments and their Order

The interdependence of cluster structure and magnetism is particularly delicate for transition metals like Mn, Cr or even y-Fe, which in the solid show antiferromagnetic order. This can be seen for example from the results presented in Table 6.1 for fcc-like 

Fei3 (bcc) Fe,3 (fee) Fei3 (ico) Fei5 (bcc) Fei9 (fee) Fe27 (bcc) Fe43 (fee) Fesi (bcc) Bulk (bcc) 

It is worth recalling that all the results discussed so far were obtained using a mean-field Hartree-Fock-type theory which neglects quantum fluctuations and which tends to overestimate the stability of ferromagnetism. An explicit treatment of electronic correlations 

---