Phys. Rev. B 85, 134424 (2012)

M. Khalid and P. Esquinazi

Abstract

We investigate the electrical and magnetic properties of low-energy H⁺-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 show 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 exhibit a negative and anisotropic magnetoresistance at room temperature. The relative magnitude of the anisotropic magnetoresistance reaches 0.4% at 250 K and 2% at 10 K, exhibiting an anomalous, nonmonotonous behavior and a change of sign below 100 K. All the experimental data indicate that hydrogen atoms alone in the few percent range trigger a magnetic order in the 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.