Structural, Magnetic Properties, and Hall Carrier Concentrations of (Co,Cu):ZnO Thin Films-The Role of Cu Ions and Annealing in Hydrogen

摘要

Using pulsed laser deposition, Zn_(0.92-x)Co_(0.08)Cu_xO (0 ≤ x ≤ 0.107) thin films were prepared on Si (100) substrates. The effect of Cu codoping on the electrical and ferromagnetic properties of Co:ZnO thin films is investigated by annealing the thin films in oxygen and hydrogen atmospheres, respectively. X-ray diffraction, X-ray absorption spectroscopy, transmission electron microscope, and X-ray photoelectron spectroscopy analyses indicated that the Co and Cu ions are incorporated into ZnO lattice. Hall measurements revealed that the electron concentration in the Zn_(0.92-x)Co_(0.08)Cu_xO thin film decreases with the increase of the Cu content. The as-deposited Zn_(0.92-x)Co_(0.08)Cu_xO thin film displayed intrinsic room temperature ferromagnetism. After annealing in hydrogen, the saturation magnetization of the films increase progressively with Cu content until a maximum value of 26.5 emu/cm3 (0.86μ_B/Co) at 3.1 at.% Cu is obtained. Then the saturation magnetization drops off as the Cu content further increases. The change of magnetization of the films is attributed to the Cu codoping and variation of oxygen vacancies in the films.