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Hydrogen-induced ferromagnetism in ZnO single crystals investigated by Magnetotransport

We investigated the electrical and magnetic properties of low-energy hydrogen-implanted ZnO single crystals with hydrogen concentrations up to 3 at.% in the first 20 nm surface layer between 10 K and 300 K. All samples showed clear ferromagnetic hysteresis loops at 300 K with a saturation magnetization up to 4 emu/g. The measured anomalous Hall effect agrees with the hysteresis loops measured by superconducting quantum interferometer device magnetometry. All the H-treated ZnO crystals exhibited a negative magnetoresistance up to the room temperature. The relative magnitude of the anisotropic magnetoresistance reaches 0.4 % at 250 K and 2 % at 10 K, exhibiting an anomalous, non-monotonous behavior and a change of sign below 100 K. All the experimental data indicate that hydrogen atoms alone in a few percent range trigger a magnetic order in a ZnO crystalline state. Hydrogen implantation turns out to be a simpler and effective method to generate a magnetic order in ZnO, which provides interesting possibilities for future applications due to the strong reduction of the electrical resistance.