Transport across a pinned domain wall across a GaMnAs constriction: from AMR to spin-dependent tunneling.

We report on the different magnetotransport mechanism across a pinned domain wall in a GaMnAs nanowire dependent on constriction size. Nanometer-sized constrictions are realized in LT-MBE epifilm GaMnAs by standard e-beam lithography and wet-etch chemistries, as well as a ``break-junction method'' to further decrease constriction size. Four-point probe DC \textit{IV} measurements- with applied fields at varying angles to wire axis- are utilized to study the transport mechanism- as well as magnetic properties. As constriction size approaches epifilm thickness, nonlinear \textit{IV }response is observed with a differing field dependence on temperature. As constrictions become smaller, we observe a tunneling AMR-like behavior. This effect is more evident after series of high current pulses are applied to decrease the constriction width. ``Break-junction'' method results in higher constriction resistances and increases in resulting MR values.