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The ferromagnetic and electrical characteristics of in situ Mn-doped GaN nanowires fabricated in the absence of any catalyst are reported. The nanowires are of single-crystal hexagonal structure, containing Mn up to 2.5 atom %. Magnetism measurements indicate that the nanowires have room temperature ferromagnetism with Curie temperature above 350 K. Magnetic force microscopy verifies that the ferromagnetism of the individual nanowire is uniform along the nanowire. An electrical transport measurement reveals that the nanowire has a weak gating effect and is of the n-type.

We have studied the spin dependent tunneling properties of Mn-doped GaN nanowires with ferromagnetic Co contacts. The magnetoresistances were measured between two ferromagnetic Co electrodes, or Co and Ti∕Au electrodes through Mn-doped GaN nanowires. The magnetoresistances of nanowire with the Co electrode indicate hysteretic behaviors, which are commonly observed in tunnel magnetoresistance devices. The magnetoresistance ratio increases from −0.6% at 20K to −9.4% at 1.74K. It is believed that the hysteretic magnetoresistances originate from the tunnel magnetoresistance effect between the ferromagnetic phases of nanowire and Co electrode.