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国家自然科学基金(11174092)

作品数:4 被引量:0H指数:0
相关作者:邱洋段寒凝伍茂松霍绍新更多>>
相关机构:华中科技大学更多>>
发文基金:国家自然科学基金更多>>
相关领域:一般工业技术理学化学工程更多>>

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Memory Effect up to Room-temperature in Ni/Ni_2P Core-shell Structured Nanoparticles
2013年
Memory effect has been studied in the system using magnetic nanoparticles with Ni nanocore encapsulated by non-magnetic and oxidation-resistant Ni2P nanoshell acquired through surface-phosphatizing Ni nanoparticles. The self-assembled array with interparticle spacing of about 6 nm shows memory effect up to 200 K below its average blocking temperature of 260 K. And reducing the interparticle spacing of the self-assembled array via annealing can further enlarge the temperature range of memory effect up to room-temperature. The memory effect can be understood based on the thermal relaxation theory of single-domain magnetic nanoparticles. Furthermore, the read-write magnetic coding is realized based on the temperature changes, using the memory effect up to room-temperature, which may be useful for future memory devices.
段寒凝YUAN SongliuZHENG XianfengTIAN Zhaoming
关键词:CORE-SHELL
Effects of A1 site occupation on dielectric and ferroelectric properties of Sr_4CaRTi_3Nb_7O_(30)(R=Ce,Eu) tungsten bronze ceramics
2014年
Sr4Ca RTi3Nb7O30(R = Ce, Eu) tungsten bronze ceramics are prepared by a standard solid state reaction method. The effects of A1 site occupation on the dielectric and ferroelectric properties of Sr4 Ca RTi3Nb7O30(R = Ce, Eu) tetragonal tungsten bronzes are investigated. The Sr4 Ca Ce Ti3Nb7O30 shows a normal transition behavior due to the closer size ion occupation in A1 sites, which could suppress the distortion of B2 octahedra effectively. Sr4 Ca Eu Ti3Nb7O30 ceramic exhibits two dielectric anomalies, which might be related to the fact that the large radius difference between Ca^2+ and Eu^3+ could lead to the uneven distribution of Ca^2+ and Eu^3+ in A1 sites and form two slightly different kinds of compositions with different transition temperatures in the structure. Our results indicate that the ionic radius difference in A1 sites plays an important role in determining the dielectric and ferroelectric natures of the filled tungsten bronze ceramics. Polarization–electric field(P–E) curves are evaluated at room temperature and both of them show hysteresis loops. Sr4 Ca Ce Ti3Nb7O30 shows a fat hysteresis loop, indicating the long-range ferroelectric order in the ceramic. The current density–electric field(J–E) curves are measured at room temperature with a largest leakage current density of ~ 10^-6A/cm^2, indicating that their leakage currents are rather low.
方玉娇龚高尚Gebru Zerihun袁松柳
关键词:RELAXATIONFERROELECTRICITY
The synthesis and exchange bias effect of monodisperse NiO nanocrystals
2012年
Monodisperse NiO nanocrystals with an average particle size of 3 -h 0.4 nm are successfully synthesized by the thermal decomposition of Ni-oleylamine complex in an organic solvent under a continuous 02 flux. The crystalline structure and the morphology of the product are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Magnetization and alternating-current (ac) susceptibility measurements indicate that the structure of the particles can be considered as consisting of an antiferromagnetieally ordered core and a spin- glass-like surface shell. In addition, both the exchange bias field and the vertical magnetization shift can be observed in this system at 10 K after field cooling. This observed exchange bias effect is explained in terms of the exchange interaction between the antiferromagnetie core and the spin-glass-like shell.
段寒凝袁松柳郑先锋田召明
关键词:ANTIFERROMAGNETICS
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