  We investigate, angle dependent, the magnetoresistance (MR) of individual
self-assembled ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires at cryogenic
temperatures. The shape of the MR traces and the observed strong anisotropies
in transport can be ascribed to the interplay of the negative magnetoresistance
effect and a strong uniaxial anisotropy with the magnetic easy direction
pointing along the wire axis. The magnetoresistance can be well described by a
quantitative analysis based on the concept of the effective magnetic field,
usually used to describe ferromagnetic resonance phenomena. The nanowires we
investigate exhibit a uniaxial anisotropy which is approximately 5 times larger
than the strain induced anisotropy observed in lithographically prepared
(Ga,Mn)As stripes.
