Study of the radiation damage caused by ion implantation in ZnO and its relation to magnetism

Defects play an important role in causing room temperature ferromagnetism in ZnO films. Multi-energy ion implantation has been employed to introduce different concentrations of non-magnetic ions, including argon, arsenic and krypton, into high-quality ZnO films and room temperature ferromagnetism has been observed for As and Kr implanted ZnO while none was observed for Ar doped films. The Monte Carlo simulation code SRIM was adopted to simulate the distributions of the implanted ions, the induced zinc and oxygen vacancies and the resulting interstitials. A common radiation damage parameter, known as the atomic displacements per atom (dpa), was calculated to quantify the primary radiation damage production. Our results show that the observed magnetic moment measured at low temperatures due to implantation with a given ion is proportional to the dpa. The constant of proportionality between the magnetism and the dpa depends on the implanted ion. This constant is largest for heavy, large ions. To obtain room temperature d0 magnetism in ZnO, non-magnetic ions with high mass are suggested to be implanted into ZnO films.