AVS 53rd International Symposium
    Electronic Materials and Processing Wednesday Sessions
       Session EM+MI-WeA

Paper EM+MI-WeA4
Room Temperature Ferromagneticism in Fe Im-planted ZnO Nanotips*

Wednesday, November 15, 2006, 3:00 pm, Room 2003

Session: Magnetic Semiconductors
Presenter: R.A. Bartynski, Rutgers University
Authors: R.A. Bartynski, Rutgers University
D. Hill, Rutgers University
D.A. Arena, National Synchrotron Light Source
P. Wu, Rutgers University
Y. Lu, Rutgers University
J.F. Al-Sharab, Rutgers University
F. Cosandey, Rutgers University
Correspondent: Click to Email
Transition metal- (TM-) doped ZnO is a promising candidate dilute magnetic semiconductor for room-temperature spintronics applications. Controlled synthesis of nanoscale structures of these materials offers the possibility to develop low-dimensional spin-dependent electronic devices. We have grown well-aligned ZnO nanotips on SiO@sub 2@/quartz substrates using MOCVD. The tips were subsequently Fe-doped to a dose 5 x 10@super 16@ cm@super -2@ using ion implantation at 200 keV. The magnetic, structural, and chemical properties of both as-implanted and post-implantation annealed nanotips were studied using SQUID magnetometry, electron energy loss (EELS) and X-ray Energy Dispersive (EDS) spectroscopy in high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and soft X-ray absorption spectroscopy (SXAS). The as-implanted tips were ferro-magnetic at room temperature with a saturation moment of ~ 0.2 µ@sub B@/Fe-ion, a remnant magnetization of ~0.03 µ@sub B@/ion, and a coercive field of ~150 Oe. The tips exhibit a core-shell structure with a high concentration (~ 8%) of Fe in the first ~ 10 nm, and about 3% in the interior, with roughly equal concentrations of Fe@super +2@ and Fe@super +3@ oxidation states. Post implantation annealing to 700C for 10 minutes improves crystallinity, produces a more uniform ~ 5% concentration of Fe, and increases the Fe@super +3@:Fe@super +2@ ratio, but significantly reduces the saturation magnetization. However, the tips remain ferromagnetic up to at least room temperature. The reduction in magnetic response, despite the increased magnetic moment/ion expected from the increased Fe@super +3@ concentration, suggests that the redistribution of Fe ions dominates the ferromagnetic coupling in the system. @FootnoteText@ * Supported by NSF Grant ECS-0224166.