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Fig. 1.10. The intersections of the Fermi surfaces, for the two spin
states of the seventh band in dhcp Pr, with the faces of the Brillouin zone
of Fig. 1.4. The surfaces are generated by a rigid splitting of the energy
bands of Fig. 1.9 by 10 mRy. The unshaded majority-spin surface is a
single sheet, whereas the exchange splitting modifies the topology of the
shaded minority-spin surface, giving rise to a closed lens at M, a small
electron pocket, and an irregular tube along HK.
and clear evidence for this transition has been observed in the dHvA
effect. The changes of the Fermi surface in a magnetic field, and partic-
ularly the enhancement of the effective masses by the interaction with
the 4 f moments (Wulff et al. 1988), which we will discuss further in Sec-
tion 7.3, give an average value of I of about 9 mRy, with a variation of
some 30% over different bands and orbits. The agreement between the
measured and calculated electron orbits is such that shifts in the energy
bands of only a few mRy are required to bring the two into concordance,
and this is comparable to typical values for transition metals (Mackin-
tosh and Andersen 1980). The experimental study of the dHvA effect in
Pr, which is the most elaborate which has yet been undertaken for a rare
earth metal, has thus led to the important conclusion that energy-band
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