In order to investigate the ferromagnetism of Codoped ZnO, we systematically fabricated Zn1-xCoxO (x=0, 0.05, 0.1, 0.2, 0.4) thin films on (0001) Al2O3 substrates by rf-sputtering and measured their structural, electronic, optical, and magnetic properties. Below 20 mol％ of Co, the Co ion could be successfully substituted at Zn site and showed clear paramagnetism in superconducting quantum interference devices (SQUID) and magnetic circular dichroism (MCD) measurements. However, secondary phases, including Co metal clustering, were found in the ZnO matrix at a 40-mol％ Co concentration, showing a strong ferromagnetism due to the contributes of microscopic precipitates of Co ions. Consequently, the clear paramagnetic behaviors of all the fabricated ZnCoO thin films in the magneto-optic MCD results revealed that the spin-polarized band structure, an intrinsic property of ferromagnetism diluted ferromagnetic semiconductors (DMSs), could not be induced by the substituted Co ions themselves. Importantly, these results indicate that any intrinsic ferromagnetism in ZnCoO cannot be induced without the contribution of hydrogen.
Co-doped ZnO DMS Magnetic secondary phases MCD
Sung-Jin Kim Il Kyoung Jeong Yong Chan Cho Su Jae Kim Seunghun Lee Won-Kyung Kim Se-Young Jeong Chae Ryong CHO Jong-Seong Bae Sungkyun Park
Department of Nano Fusion Technology, Pusan National University, Miryang 627-706 Department of Physics Education, Pusan National University, Busan 609-735 Department of Cogno-Mechatronics Engineering, Pusan National University, Miryang 627-706 Department of Nanomedical Engineering, Pusan National University, Miryang 627-706 Korea Basic Science Institute, Busan Center, Busan 609-735 Department of Physics, Pusan National University, Busan 609-735