  We report on magnetotransport measurements of nanoconstricted (Ga,Mn)As
devices showing very large resistance changes that can be controlled by both an
electric and a magnetic field. Based on the bias voltage and temperature
dependent measurements down to the millikelvin range we compare the models
currently used to describe transport through (Ga,Mn)As nanoconstrictions. We
provide an explanation for the observed spin-valve like behavior during a
magnetic field sweep by means of the magnetization configurations in the
device. Furthermore, we prove that Coulomb-blockade plays a decisive role for
the transport mechanism and show that modeling the constriction as a granular
metal describes the temperature and bias dependence of the conductance
correctly and allows to estimate the number of participating islands located in
the constriction.
