The Magnetic Properties Of Non-magnetic Metal Doped Bis(8-hydroxyquinoline)Cobalt Films

Magnetic materials have been employed in a truly wide range of applications and played an important role in modern life. Besides the traditional inorganic magnetic materials, such as magnetic metals, alloys and ferrites, magnetic materials also include organic magnets. The magnetism in traditional magnets is usually derived from the unpaired electrons of the d shells in the transition metals and their oxides or the f shells in rare earth elements. Organic materials are mainly combined by covalent bonds with paired electrons. They generally do not show paramagnetic or ferromagnetic behaviors. However, ferromagnetism was found in certain organic compounds with a stable free radical, as well as in the organic complexes containing transition metals. Organic magnets have attracted intense efforts during the past few decades, as they are cheap, low-weight, mechanically flexible and chemically interactive. In particular, they can be fabricated through controllable low-temperature methods, as opposed to high-temperature metallurgical routes for inorganic magnets.Doping transition metals into small organic molecules is an important method of preparing organic magnetic semiconductors. In2008, J.M.Baik et al. reported ferromagnetism in3d transition Co metals doped tris(8-hydroxyquinoline)aluminum (Alq3) thin films synthesized by thermal co-evaporation of pure Co metal and Alq3powders. The Curie temperature of Mn doped Alq3film also reaches270K. However, the process of co-evaporating of3d transition metal and organic molecules is very hard to control. There is a probability that magnetic metal clusters exist in the film, which leads the magnetism of the film uncertain.In this thesis, the pure and non-magnetic metal doped bis(8-hydroxyquinoline)cobalt films are prepared by thermal co-evaporation. Bis(8-hydroxyquinoline)cobalt may have intrinsic magnetic properties because of the partially occupied3d states in Co atoms. The doped non-magnetic atoms (Cu, Al) may enhance the coupling between the local magnetic moments, so as to enhance the total magnetic moment. Because no transition metals were used, magnetic metal clusters can be avoided.The main contents and conclusions are as follows: (1) Pure Coq2films with a thickness of100nm were prepared by vacuum thermal evaporation. Morphology analysis by AFM showed a good film quality. By using the FT-IR for the structural analysis, we observed the characteristic vibrational peaks of hydroquinone ligands and pyridine rings in700-1200cm-1. Pure Coq2film shows paramagnetic behavior at low temperature (5K).(2) We prepared a series of Al doped Coq2films. AFM, EDS, FT-IR, AGM and SQUID were used to test the morphology, composition, structure, and magnetic properties of the samples, respectively. The films showed a slightly rougher surface morphology than that of pure Coq2. The EDS result showed that the doping ratio of the sample by co-evaporation was in line with the expectation. FT-IR structural analysis showed that the vibration peak at410cm-1had a blue shift in Al-doped film, indicating that the doped metals had bonded with the Coq2molecules. The SQUID and AGM experiments showed that the Al-doped Coq2films had intrinsic ferromagnetism. The saturation magnetization of the samples increased with the temperature and the doping ratio, while the coercivity decreased with the temperature.(3) We prepared a series of Cu-doped Coq2films. The RMS(Rq) is1.27nm, which is larger than that of pure and Al-doped Coq2. FT-IR showed that the vibration peak at410cm-1had a redshift, indicating that the doped metals had bonded with the Coq2molecules. The magnetic tests showed that the Cu-doped Coq2films had intrinsic ferromagnetic properties.