Magnetism Stoner criterion

In the Stoner theory for magnetism, it is shown that magnetic ordering is possible in a band scheme, when spin-polarization is energetically favorable the full discussion (see Chap. A) for the simpler case of ferromagnetism leads to a simple criterion known as the Stoner criterion ... 

From band structure calculations as well as from experimental results (photoemission, specific heat...), it is now clear that, at least for magnetic compounds near the critical spacing, 5 f electrons are in bands. This means that contrary to the pure metals, the Stoner criterion may be fulfilled before the band description breaks down. 

These experimental results received theoretical support from band calculation results, Brooks found that for UN and PuN the Stoner criterion was just satisfied and that these nitrides were itinerant magnetic systems. 

Long-range magnetic order and the Stoner Criterion... 

Clearly, the critical parameter that must be evaluated is simply the Modified Stoner Factor N(Ef)Ixc - if this exceeds unity then the magnetic energy will become negative and spontaneous magnetisation will become favourable. This is the so-called Stoner Criterion . Janak [6] has calculated l c for several elements, providing an insightful commentary on trends in this quantity across the periodic table. 

The reason for the general enhancement in surface magnetic moment is rather clear, as the narrowing of the rf-band due to removal of the nearest neighbours from the surface-layer atoms increases the Fermi level DOS and locally pushes the system further beyond the critical limit of the Stoner Criterion. The effect is presumably larger for bcc Fe in part because the reduction in nearest neighbours from eight to four is a more radical perturbation than from twelve to nine in both hep Co and fee Ni. 

Long-Range Magnetic Order and the Stoner Criterion 262... 

To complete the discussion, we examine the magnetic susceptibility x of a system in which spontaneous magnetization arises when the Stoner criterion is met. We... 

The Stoner criterion provides some insight into the differences in magnetic properties that are expected to exist in thin films and surfaces. The Stoner parameter and the DOS at the Fermi level depend on the chemical elements and the system s dimensionality and can thus be modified. The DOS at the Fermi level depends on the width of the d-band, which can be roughly described as... 

From Table 8.6, it can be seen that the Stoner parameter for Pd is 0.025 Ry, or 0.34 eV. The DOS at the Fermi energy is given as N(Ef) = 2.28 eV. Their product is 0.7752, which is less than unity and, therefore, does not satisfy the criterion for magnetic behavior. 

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