ELEMENTS OF RARE EARTH MAGNETISM - Rare Earth Magnetism: Structures and Excitations - page 47

Fig. 1.17. The exchange interaction J S ( q ) −J S ( 0 ), determined ex-
perimentally in the magnetic heavy rare earth metals. The magnitude
of the peak, which stabilizes the observed periodic magnetic structures,
increases monotonically with atomic number.

A notable feature is the maximum which, except in Gd, occurs at non-
zero q and, as discussed in the following section, is responsible for stabi-
lizing the periodic magnetic structures in the metals. In the approxima-
tion which we have used, the conduction-electron susceptibility is given
by

χ ( q )= 2 µ 2 B
V

f n k − q
ε n ( k − q )

f n k −

ε n ( k ) ,

(1 . 4 . 23)

−

nn k