  We consider the dependence magnetization vs. field at zero temperature for
the spin-1/2 chains in which the intersite interactions regularly vary from
site to site with a period p. In the limiting case when the smallest value of
the intersite interactions tends to zero the chain splits into noninteracting
identical fragments of p sites and the dependence magnetization vs. field can
be examined rigorously. We demonstrate explicitly the appearance of plateaus in
such dependence and discuss a presence of the magnetization values m predicted
by the condition p(1/2-m)=integer [1]. We comment on the influence of the
anisotropy in the interspin interaction on the magnetization profiles. Finally,
we show how the case of nonzero smallest value of the intersite interactions
can be considered.
