  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.
