Ferromagnetic alignment

Fig. 2 Representation of the ferromagnetic alignment of d localized spins resulting from the interaction with itinerant electrons through short intermolecular contacts...

Figure 9.5 Schematic representation of a bound magnetic polaron (a) one bound magnetic polaron located on a charged defect and (b) overlapping bound magnetic polarons leading to ferromagnetic alignment of magnetic ions.

Very direct evidence for the existence of bound spin polarons is provided by the work of Torrance et al (1972) on the metal-insulator transition in Eu-rich EuO At low temperatures, when the moments on the Eu ions are ferromagnetically aligned, the electrons in the oxygen vacancies cannot form spin polarons and are present in sufficient concentration to give metallic conduction. Above the Curie temperature the conductivity drops by a factor of order 10 , because the electrons now polarize the surrounding moments, forming spin polarons with higher effective mass. 

Scheme 7 Spin alignment for a paramagnet (left) and ferromagnet (middle) in zero external magnetic field, and ferromagnetic aligned by external magnetic field.

According to the model for ferromagnetic alignment proposed by McConnell, which is based on configuration interaction along a D+A D+A-chain (28), and confirmed by studies on (Cp2Fe)(TCNE) and (3-(Cp)Fe)-[Pt(mnt)2] mentioned above, an alternation between the acceptor anion-radical... 

Figure 12.10 Double exchange, possible only with ferromagnetic alignment of spins on cations...

Figure 7.14 Double exchange, schematic a cation, left, transfers a spin-up electron to an oxygen p orbital, centre (arrow), which simultaneously transfers a spin-up electron, right (arrow), to an empty orbital on the receiving cation, forcing ferromagnetic alignment of spins. The interaction is illustrated for HS MrP (3d", t ) and HS Mn (3d, ti) cations...

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