  The large saturation magnetization in conventional dense moment ferromagnets
offers flexible means of manipulating the ordered state through demagnetizing
shape anisotropy fields but these dipolar fields, in turn, limit the
integrability of magnetic elements in information storage devices. We show that
in a (Ga,Mn)As dilute moment ferromagnet, with comparatively weaker magnetic
dipole interactions, locally tunable magnetocrystalline anisotropy can take the
role of the internal field which determines the magnetic configuration.
Experiments and theoretical modeling are presented for lithographically
patterned microchannels and the phenomenon is attributed to lattice relaxations
across the channels. The utility of locally controlled magnetic anisotropies is
demonstrated in current induced switching experiments. We report structure
sensitive, current induced in-plane magnetization switchings well below the
Curie temperature at critical current densities 10^5 Acm^-2. The observed
phenomenology shows signatures of a contribution from domain-wall
spin-transfer-torque effects.
