Diluted Magnetic Semiconductor Cobalt and Europium Implanted ZnO Thin Film

Abstract

Diluted magnetic semiconductors (DMSs) have initiated enormous scientific interests because of their potential for multifunctional spintronics devices. ZnO based semiconductors have been identified to be the promising room temperature ferromagnetic materials with a wide band-gap. However, the intrinsic room temperature ferromagnetic spintronics materials are still far to be optimized. In this dissertation, the samples were prepared by using metal vacuum vapour arc (MEVVA) source ion implantation of cobalt and europium into ZnO/c-Al2O3 (0001) epitaxial thin films. The ion implantation is an effective technique for introducing dopants of heavy elements into thin film. The depth profile of as-prepared sample as well as dopants concentration was studied by ion beam analysis and transport of ions in matter (TRIM) calculation. It was found that the total magnet moment of Co doped ZnO was improved by additional Eu doping. The correlation between the properties of Zn1-xEuxO and Zn1-xCox-yEuyO system and local coordination chemical environment as well as the underlying mechanism was investigated in details.The superconducting quantum interface device (SQUID) magnetometer shows all as-prepared samples are ferromagnetic at room temperature. However, it is unclear whether such a phenomenon is an intrinsic property or caused by the Co metallic clusters. The X-ray magnetic circular dichroism (XMCD) shows that the strong spin polarization of localized Eu atoms observed near surface of the Zn1-xEuxO thin films. The XMCD results also suggest Eu implanting to ZnO:Co system has suppressed Co metallic clustering. X-ray absorption fine structure (XAFS) confirms that Eu3+ had substituted for Zn2+ and resided in tetrahedral geometry without changing the wurtzite structure of ZnO host lattice in Zn1-xEuxO; whereas substitutional Co2+ and Co metallic clusters are coexisting in Zn1-xCoxO. But the Co clustering fraction can be significantly decreased by adding Eu into Zn1-xCoxO through ion implantation. The experimental and theoretical studies suggest a short range interaction between the substitutional Eu3+ is anti-ferromagnetic in Zn1-xEuxO. The experimental results provide guidance to develop the new materials to enhance the intrinsic ferromagnetic properties of ZnO based DMSs via rare earth element implantation