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The Studies on the Electrochemical Deposition, Structures and Performance of the Iron Group Magnetic Films

Author: LiZongMu
Tutor: XuFaQiang
School: University of Science and Technology of China
Course: Synchrotron Radiation and Applications
Keywords: electrodeposition magnetic film magneto-optical Kerr effect X-ray absorption synchrotron radiation X-ray magnetic circular dichroism oriented attachment
CLC: TB383.2
Type: PhD thesis
Year: 2007
Downloads: 375
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Abstract

Although the people have known and begun to use the magnetic properties of materials as long as 4,000 years, new magnetism related phenomena are still emerging in continually up to now. Today, magnetic materials have been applied in many fields, especially in the information storage. The properties of semiconductors were known well later, while their applications in information processing have been developed very greatly. For a long time, the technologies of information storage and information processing had been developed independently. With the miniaturization of electronic devices and the development of nanotechnologies, the spintronics appeared, which combined the research areas of magnetic materials and semiconductors. As the development of spintronics, the integration of the magnetic materials and semiconductors has attracted more and more attentions. Though the MBE method is one of the best techniques to deposit ferromagnetic metals on semiconductor surfaces, the interdiffusion and interaction of magnetic atoms with the substrates have been being a hindrance to obtain optimal device performance. The electrochemical deposition is a low energy process, which can form a sharp interface between the film and substrate, so the problem of interracial diffusion can be resolved effectively. Up to now, most of the studies on electrodeposition of magnetic metals on semiconductors have been focused on the electrodeposition methods, components, morphologies and macroscopic magnetism of the films and few researches were centered on microscopic magnetism and local magnetic moment of alloy films. In this paper, cyclic voltammetry is used to fabricate the films of pure metals and alloys for the Fe group elements. Synchrotron radiation X-ray magnetic circular dichroism （XMCD）, combining with the X-ray diffractmeter （XRD）, scanning electronic microscopy （SEM）, magneto-optical Kerr effect （MOKE）, atom force microscope/magnetic force microscope （AFM/MFM） and X-ray absorption spectroscopy （XAS） techniques are employed to systematically investigate the structures and properties of the films. 1. A magneto-optical Kerr effect （MOKE） setup with the sensitivity of about 1 nm was assembled using He-Ne laser, chopper, polarizer, photodiode, lock-in amplifier, electro-magnet and industrial computer. This equipment can be used to investigate the Kerr effect, the Kerr rotation and the magnetic hysteresis loops of the magnetic films as well as the in-plane magnetic anisotropy of some films by rotating the magnetic films in plane.2. The Fe, Co and Ni films were respectively deposited on GaAs（100） by cyclic voltammetry using a three-electrode system in the solution containing 0.1 mol/L （NH₄）₂Fe（SO₄）₂, COSO₄, NiSO₄ with pH～2.5. The spin and orbital magnetic moments of the films were calculated by applying the sum rules. The results showed that the magnetic moment of Co atom was 1.812μ_B, which was consistent with the value in the literatures, while the magnetic moments of Fe and Ni were 1.615μ_B and0.551μ_B, respectively, which are smaller than the values reported in the literatures. One of the possible reasons that lead to the decrease of magnetic moments may be retated to the preparation method of the films.3. The Fe₆₇Co₃₃、Fe₂₁Ni₇₉、Co₆₆Ni₃₄, Fe₂₈Co₅₁Ni₂₁ films were respectively deposited onto GaAs（100） substrate using cyclic voltammetry in different solutions. The AFM image of Fe-Co alloy film showed that the alloy film was composed of particles with the size of 20 nm and the MFM photograph indicated that the particles in film are ferromagnetic coupling. The SEM image of Co-Ni alloys film gave that the diameter of particles is about 40 nm and the particle sizes in Fe-Co-Ni film is about 60-120nm displayed in SEM and AFM images. The results of Kerr magnetic hysteresis loops revealed that the alloy films are all good rectangle magnetic materials and do not have the in-plane magnetic anisotropy except the Co-Ni film. Using the XMCD technology, the element-specific magnetic hysteresis loops of Fe-Co alloy film were obtained, which indicated that the Fe and Co in alloy are ferromagnetic coupling based on the saturation magnetic field and coercive force. The XMCD spectra of the alloy films were obtained by measuring the XAS spectra of the alloy films using the circularly polarized synchrotron radiation and the spin and orbital magnetic moments of Fe, Co, Ni were calculated by applying the sum rules. It was found that the average atomic magnetic moments of Fe and Co almost did not change while that of Ni was increased evidently during the alloying processes.4. A new method to measure the magnetic hysteresis loops of magnetic films has been established in the XMCD endstation based on the synchrotron radiation XMCD technology. This method can not only measure the magnetism of pure metal, but also obtain the contribution of each element to the macroscopic magnetism of the alloy as well as the magnetic coupling between the components.5. ZnO crystals with intergrowth structures were prepared in vapor by designing a novel setup. SEM and XRD results showed that the products were composed of high quality ZnO microcrystals and the PL spectrum of the ZnO complex structure showed a strong ultraviolet emission at～382 nm and a weak green emission at～520 nm. We proposed that the growth mechanism of the complex ZnO 3D structure was explained reasonably by the oriented attachment of ZnO crystallites in gas phase.

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