  Here we report on detailed studies of the magnetic properties of the wurtzite
(Ga,Mn)As cylindrical shells. Ga$_{0.94}$Mn$_{0.06}$As shells have been grown
by molecular beam epitaxy at low temperature as a part of multishell cylinders
overgrown on wurtzite (Ga,In)As nanowires cores, synthesized on GaAs (111)B
substrates. Our studies clearly indicate the presence of a low temperature
ferromagnetic coupling, which despite a reasonably high Mn contents of 6\% is
limited only to below 30~K. A set of dedicated measurements shows that despite
a high structural quality of the material the magnetic order has a granular
form, which gives rise to the dynamical slow-down characteristic to blocked
superparamagnets. The lack of the long range order has been assigned to a very
low hole density, caused primarily by numerous compensation donors, arsenic
antisites, formed in the material due to a specific geometry of the growth of
the shells on the nanowire template. The associated electrostatic disorder has
formed a patchwork of spontaneously magnetized (macrospin) and nonmagnetic
(paramagnetic) volumes in the material. Using high field results it has been
evaluated that the total volume taken by the macrospins constitute about 2/3 of
the volume of the (Ga,Mn)As whereas in the remaining 1/3 only paramagnetic Mn
ions reside. By establishing the number of the uncoupled ions the two
contributions were separated. The Arrott plot method applied to the
superparamagnetic part yielded the first experimental assessment of the
magnitude of the spin-spin coupling temperature within the macrospins in
(Ga,Mn)As, $T_{\mathrm{C}}=28$~K. In a broader view our results constitute an
important contribution to the still ongoing dispute on the true and the
dominant form(s) of the magnetism in this model dilute ferromagnetic
semiconductor.
