Observation of the Strong Negative Anomalous Hall Effect in Co-ion-implanted ZnO Single Crystals

Abstract

Eighty-keV Co ions with a dose of 3 x 10(16) ions/cm(2) were implanted into high-quality 0.5-min-thick ZnO (0001) single crystals with very low carrier concentration of n = 2.0 x 10(13)/cm(3). The implanted samples were post-annealed at 700, 800, and 900 degrees C by rapid thermal annealing in a N-2 atmosphere. The structural, magnetic, and transport properties of Co-ion-implanted ZnO were investigated. The Co X-edge, extended X-ray absorption fine structure analysis revealed the coexistence of Co-Co and Co-Zn bonds. The Co ions substituted into Zn sites form Zn1-xCoxO. Magnetoresistance (MR) data showed a sign change from positive to negative between 50 K and 77 K. A strong negative anomalous Hall effect (SNAHE) was observed in the temperature range with a positive MR. The sign change in the observed SNAHE seems to support the theory of Burkov and Balents.