Chemistry Reference
In-Depth Information
(a)
A
B
(b)
B
A
Figure 7.3
(a) When the electron spins are anti-parallel in a diatomic molecule, there
can be a high probability of both electrons being between the two nuclei
(A and B), maximising the electron-nuclear attractive interaction. (b) By
contrast, when the spins are parallel, the electrons tend to avoid each
other more, leading to a weaker overall electron-nuclear interaction.
Conduction
electron
Atom A
Atom B
Figure 7.4
Indirect exchange interaction in a metal. The magnetic moment, for exam-
ple, on atom A has a direct exchange interaction with a free conduction
electron, influencing the spin of the conduction electron. The conduction
electron then interacts with an electron on atom B, which can enable a large
indirect exchange interaction between the magnetic moments on A and B.
spin dependence of the exchange energy of the whole solid:
H
=−
J
ij
s
i
·
s
j
(7.4)
i
i
=
j
The contribution to the total exchange energy due to the interaction
between atoms
i
and
j
,
E
ex,
ij
, is then given by
E
ex,
ij
=−
2
J
ij
s
i
·
s
j
(7.5)
