Fabrication, Microstructure And Magnetic Properties Of NiO And Ni/NiO Composite Nanoparticles

Bulk NiO is antiferromagnetic, the neel temperature of which is 523 K. NiO is also an important semiconductor, with forbidden band width around 4 eV. This makes NiO have important applicationsin the photovoltaic (pv) and electronic devices, magnetic materials and other industries. During the process of the studying the magnetic properties of NiO nanoparticles, magnetic enhancement, big coercivity, spin glass freeze and unusual hysteresis phenomenon have been found, which is quite different from bulk NiO. Besides, there is interfacial coupling effect in Ni/NiO nanocomposites, thus having an remarkable effect on the magnetic properties such as exchange bias. This paper mainly includes the following two aspects:(1) NiO nanoparticles were prepared by means of pyrolysis synthesis. Through XRD, we can get the structure of NiO nanoparticles is fcc. By SEM and TEM, we can observe that most samples are spherical particles (sub)micron in size, which are made up of particles smaller in size. Besides, surfactant have great influences on the morphology of the sample. By uv-vis absorption spectrum, we can estimate the forbidden band width of the NiO nanoparticles, and it is concluded that the forbidden band width decreases with the increase of particle size. By VSM and SQUID, we found the coercivity of some nano NiO nanoparticles at room temperature is up to 269.0 Oe. This abnormal magnetic properties are difficult to explain with double sublattice antiferromagnetic ordered theory which is applicable to to block material.(2) Ni/NiO nanocomposites were prepared by means of pyrolysis synthesis. Through XRD and XPS, we can get the structure of Ni/NiO nanocomposite is fcc and the valence state of Ni is 0 and+2. By SEM, we can observe that most samples are spherical particles (sub)micron in size, which are made up of particles smaller in size. Lattice fringe and interface can be clearly observed by TEM and SAED. The results of SQUID showed the coercivity of Ni/NiO nanocomposites at 5 K is up to 1068 Oe, and the exchange bias is about 350 Oe. With the decline of Ni weight fraction from 20.7% to 2.6%, there is rise of coercivity He and exchange bias HE from 6 Oe to 350 Oe. In addition, the blocking temperature of Ni/NiO nanocomposites is higher than 350 K.