  We study the probability of formation of ferromagnetic string in the
antiferromagnetic spin-1/2 XXZ chain. We show that in the limit of long strings
with weak magnetization per site the bosonization technique can be used to
address the problem. At zero temperature the obtained probability is Gaussian
as a function of the length of the string. At finite but low temperature there
is a crossover from the Gaussian behavior at intermediate lengths of strings to
the exponential decay for very long strings. Although the weak magnetization
per site is a necessary small parameter justifying our results, the
extrapolation of obtained results to the case of maximally ferromagnetic
strings is in qualitative agreement with known numerics and exact results. The
effect of an external magnetic field on the probability of formation of
ferromagnetic strings is also studied.
