Preparation And Magnetic Properties Study Of Alumina Films

Low-dimensional materials, such as thin films of HfO2, TiO2, In2O3, ZnO, CeO2 and nanoparticles, have recently attracted great attention because of their potential application in spintronics. Sundaresan et al. have observed the room temperature ferromagnetism (FM) in Al2O3 nanoparticles, and considered that ferromagnetism was the usual property of nanoparticles. Alumina is a wide-band-gap semiconductor that has been widely used in spintronics applications. It has good thermal stability and high corrosion resistance, and it can work in high temperature and high corrosion circumstance.We have prepared Al2O3-δfilms and Al2O3-δ-based composite films by radio frequency. The magnetism properties, microstructure, electrical transport properties, of the films were characterized. The results are as follows:1. The alumina thin films were prepared on the Si substrates using radio frequency method. The samples were annealed in different atmosphere at different temperature. Magnetic results reveal that the film which was annealed in vaccum had a clear hysteresis loop with the largest saturation magnetization (Ms) being 4.6 emu/cm3. When the films were annealed in air, the value of Ms decreased as the annealing temperature increased. Moreover, a second series of films having different thicknesses were prepared and annealed in vacuum at 800℃. Magnetic results reveal that Ms of the films decreased dramatically with increasing thickness. We also investigated the capacitance-voltage (C-V) characteristics of the samples, and calculated the the number of fixed surface charges per unit area (Nfc). We propose that the unpaired electron spins responsible for FM in Al2O3-δfilms have their origin in oxygen vacancies, especially at the interface of the Al2O3-δfilms and the Si substrates.2. The Si-Al2O3-δcomposite films were deposited on the Si substrates by radio frequency method. Magnetic results show that the Ms of the samples increased at first and then decreased as the Si content increased. When the volume fraction of Si was 15 vol.%, the sample has the largest Ms (1.78 emu/cm3), the coercive force was found to be 110 Oe. Magnetic domain structures was observed by magnetic force microscopy (MFM). Annealing in Ar atmosphere decreased the Ms of the film. We have concluded that magnetism of the sample have relation with the interface between the Si and Al2O3-δ. 3. The C-Al2O3-δcomposite films were deposited on the Si substrates by radio frequency method. Room temperature ferromagnetism were observed in all the samples. The ferromagnetism of the films did not originate from the magnetic impurity, and it’s the intrinsic properties of the samples. The Ms of the samples increased at first and than decreased as the the C content increased. When the volume fraction of Si was 2 vol.%, the sample has the largest Ms (4.9 emu/cm3). Annealing the sample in Ar atmosphere decreased the Ms of the film. We have concluded that room temperature ferromagnetism originate from the interface between the C and Al2O3-δ.4. The Cu-Al2O3-δcomposite films were deposited on the Si substrates by radio frequency method. Room temperature ferromagnetism were observed in the samples. Annealing the sample in the air increased the Ms dramatically. We have concluded that the room temperature ferromagnetism of the samples originate from the unpaired electron spins in 3d shell of Cu2+.