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Báo cáo hóa học: " Magnetic Anisotropic Energy Gap and Strain Effect in Au Nanoparticles"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Magnetic Anisotropic Energy Gap and Strain Effect in Au Nanoparticles | Nanoscale Res Lett 2010 5 25-30 DOI 10.1007 s11671-009-9438-z NANO EXPRESS Magnetic Anisotropic Energy Gap and Strain Effect in Au Nanoparticles Po-Hsun Shih Sheng Yun Wu Received 1 April 2009 Accepted 9 September 2009 Published online 22 September 2009 to the authors 2009 Abstract We report on the observation of the size effect of thermal magnetization in Au nanoparticles. The thermal deviation of the saturation magnetization departs substantially from that predicted by the Bloch T-law indicating the existence of magnetic anisotropic energy. The results may be understood using the uniaxial anisotropy Heisenberg model in which the surface atoms give rise to polarized moments while the magnetic anisotropic energy decreases as the size of the Au nanoparticles is reduced. There is a significant maximum magnetic anisotropic energy found for the 6 nm Au nanoparticles which is associated with the deviation of the lattice constant due to magnetocrystalline anisotropy. Keywords Nanoparticles Magnetic anisotropy Magnetic properties Spin waves Introduction Metal nanoparticles of Pd Au and Cu have been extensively studied because due to a reduction in dimensionality their ferromagnetic polarizations are quite different from those observed in transition metals 1-6 . The most frequent effects of the small size are lattice rearrangement crystalline imperfections a higher degree of localization and narrowed valence band width. It has been reported in previous studies 2 4 that individual Pd and Au nanoparticles may reach their ferromagnetic moment at low temperatures and that theoretically there may be a slight P.-H. Shih S. Y. Wu H Department of Physics National Dong Hwa University Hualien 97401 Taiwan e-mail sywu@mail.ndhu.edu.tw enhancement of the 4d localization although Pd and Au are both characterized by diamagnetism in the bulk state. Bulk Au metal also demonstrates a typical diamagnetic response of -1.42 X 10-6 emu g 7 when the Xe 4f145d106 s1 Au configuration has a closed