Room temperature ferromagnetism of GaMnN thin film is awaked by a mild hydrogenation treatment of a sample synthesized by molecular beam epitaxy. Local environment of Mn atoms is monitored by Mn-L2,3 near edge x-ray absorption fine structure technique. Doped Mn ions are present at substitutional sites of Ga both before and after the hydrogenation. No secondary phase can be detected. Major valency of Mn changes from 3+ to 2+ by the hydrogenation. The present result supports the model that the ferromagnetism occurs when Mn2+ and Mn3+ are coexistent and holes in the midgap Mn band mediate the magnetic coupling.

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The presence of the residual hydrogen can be ascribed to the use of NH3 for MBE growth.

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