Hydrogen Control of Ferromagnetism in a Dilute Magnetic Semiconductor

We show that upon exposure to a remote dc hydrogen plasma, the magnetic and electronic properties of the dilute magnetic semiconductor Ga_1-xMnₓAs change qualitatively. While the as-grown Ga_1-xMnₓAs thin films are ferromagnetic at temperatures T70 K, the samples are found to be paramagnetic after the hydrogenation, with a Brillouin-type magnetization curve even at T=2 K. Comparing magnetization and electronic transport measurements, we conclude that the density of free holes p is significantly reduced by the plasma process, while the density of Mn magnetic moments does not change.