Appealing stable room-temperature ferromagnetism by well-aligned 1D Co-doped zinc oxide nanowires

Journal: Journal of Alloys and Compounds (click here for full paper)

Authors: Jamal Kazmi, Poh Choon Ooi, Syed Raza Ali Raza, Boon Tong Goh, Siti Shafura A. Karim, Mohd Hazrie Samat, Min Kai Lee, M.F. Mohd. Razip Wee, Mohamad Fariz Mohamad Taib, Mohd Ambri Mohamed.

Contact details for further info: ambri@ukm.edu.my

Summary:

Certainly diluted magnetic semiconductor Zn_1−xCo_xO has been investigated over the years, yet the morphological aspects and the structural influence on the magnetic properties of Co-doped ZnO nanowires still needs a clear understanding. The 1D magnetic nanowires possess exceptional magnetic properties and potential candidate as magnetic devices, because ideal magnetic density of 1D NWs is 200,000-fold than the currently used magnetic disks. Herein, the Zn_1−xCo_xO (x = 2.5%, 5%, 10% and 15%) 1D nanowires with Curie temperature above the room temperature have been synthesized by a simple low-temperature (65 °C) hydrothermal method. The prepared samples have been investigated by various techniques that include field emission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, micro-Raman spectroscopy, X-ray photoelectron spectroscopy, UV–vis absorption, and superconducting quantum interference device. The experimental data was further confirmed by the density functional theory calculations to affirm our findings. Structural analysis indicated the wurtzite crystal structure of NWs with preferred growth in the (001) direction along the c-axis. XPS indicated presence of OH^– groups on the surface of NWs, and as the Co content increases, there is a gradual change in the portion of Co⁺⁺ ions into Co⁺⁺⁺. Optical properties have shown decreased optical bandgap with increased doping and increased electronic concentration in the host ZnO and Raman analysis suggested fewer defects in the Co-doped ZnO NWs. By magnetic properties investigation, it was found that the Co ions substitute Zn ions in the wurtzite ZnO structure with no observation of metallic or oxide-rich phase. The magnetic moment per Co atoms of Co-doped ZnO NWs increased sigificantly compared to pure ZnO NWs. By density functional theory studies, the net magnetic moment of Co-doped ZnO NWS was recognized primarily by the exchange of spin-polarized Co-3d and adjacent electrons in the O-2p states. Henceforth, double-exchange in 3d electrons was dominant, and the Co-doped ZnO system turned out to be ferromagnetic which is consistent with our experimental findings.