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121.
ZHANG Shu-Qun CHEN Zhi-De 《理论物理通讯》2008,50(7):248-252
Spin parity effect on magnetic relaxation by quantum tunneling in the biaxial spin model is studied by taking into account the transverse local stray field. It is shown that the square root time dependence in the even resonance occurs in the presence of a distribution of transverse anisotropic parameters, while the odd resonance always shows exponential relaxation. Magnetic relaxation under a sweeping field is also studied. The variation of the relaxation curve with the increasing distribution width of the local stray field for even resonance is qualitatively different from that of the odd resonance. The theoretical result on even resonance is in agreement with experimental results on Fe8 system, while the prediction for odd resonance awaits the experimental verification. 相似文献
122.
This paper presents the analytical and simulation responses of the closed orbit distortion in the SSRF storage ring to random and plane wave like magnet vibrations respectively. It is shown that the use of girder is very beneficial in the view of suppressing this response function. Effect of the independently supported gradient bending magnets to the closed orbit response is given. An analytic formula is written to give a rough estimate of the closed orbit distortion due to ground motion, taking into account the closed orbit response function and girder transfer function. As an example, the result of SSRF case is given. 相似文献
123.
T. Idehara T. Saito H. Mori H. Tsuchiya La Agusu S. Mitsudo 《International Journal of Infrared and Millimeter Waves》2008,29(2):131-141
Long pulse operation up to 1 msec of a high frequency gyrotron with a pulse magnet has been successfully carried out in a
frequency range including 1 THz. In the experiments, the timing of an electron beam pulse injection is adjusted at the top
of the magnetic field pulse, where the variation of field intensity is negligible. The operation cavity modes seem to be TE1, 12 and TE4,12 at the second harmonics. The corresponding frequencies are 903 GHz and 1,013 GHz, respectively. Additionally several features
of radiation measurement results of the gyrotron are described and brief considerations are presented. 相似文献
124.
Rapidly solidified nanocomposite Nd9Fe77−xB14Tix alloys, consisting of magnetic Nd2Fe14B phase and soft magnetic phases, were investigated. The effect of titanium addition on the structure and magnetic properties was studied. It was found that 2–4 at% Ti addition leads to substantial increase of the coercivity and maximum energy product, maintaining the remanence unchanged. The highest properties: Jr=0.81 T, JHc=907 kA/m, (BH)max=99 kJ/m3, were achieved for the Nd9Fe73B14Ti4 alloy. This effect we attribute to the formation of fine and homogeneous grain structure and a change of the phase morphology in the Ti-containing alloys. The initial magnetization curve indicates a change of the coercivity mechanisms giving rise to pinning of domain walls, which is caused by reduction of the crystallite size. 相似文献
125.
J.T. Elizalde-Galindo J.L. Hidalgo C.E. Botez J.A. Matutes-Aquino 《Journal of magnetism and magnetic materials》2008,320(14):e222-e225
Nanocrystalline Sm0.5Y0.5Co5 powders with high coercivity HC and enhanced remanence Mr were prepared by mechanical milling and subsequent annealing. Annealing temperatures T ranging from 973 to 1173 K, and times t ranging from 1 to 5 min were used. X-ray diffraction (XRD) and DC-magnetization measurements were carried out to study the microstructure and magnetic properties of these samples. XRD patterns demonstrate that the average grain size D of the nanocrystalline powders depends on the annealing temperature T and time t: D ranges from 11 nm (for T=973 K and t=1 min) to 93 nm (for T=1173 K and t=5 min). Magnetic measurements performed at room temperature indicate high coercivity values (HC>955 kA/m), and enhanced remanence (Mr/Mmax>0.5) for all samples. A strong annealing-induced grain size dependence of these magnetic properties was found. 相似文献
126.
J.T. Elizalde-Galindo F.J. Rivera Gmez J.A. Matutes-Aquino C.E. Botez 《Journal of magnetism and magnetic materials》2008,320(14):e58-e60
Nanostructured YCo5 (70%wt)+Y2Co17 (30%wt) composite powders were prepared by mechanical milling and subsequent annealing at 1073 K for 1.5 min. The average grain size D of the YCo5 and Y2Co17 phases, obtained from XRD data, was 14 and 12 nm, respectively. The temperature dependence of the magnetic properties was studied by DC magnetization measurements at temperatures T ranging from 3 to 300 K. Hysteresis loops (Hmax=70 kOe) show that both the coercivity HC and the squareness σr/σmax are temperature-dependent. The coercivity increases from 12 kOe at room temperature to 18 kOe at T=3 K. The observed enhanced remanence (σr/σmax>0.5) indicates that a strong exchange coupling is present at all temperatures used in this study. The maximum magnetization σmax changes little with temperature and has a value of about 70% of the effective saturation magnetization of the title compound. 相似文献
127.
Nanostructured Pr8Fe86−xVxB6−yCy (x=0, 1; y=0, 1) ribbons composed of Pr2Fe14B and α-Fe phases with a high coercivity are fabricated by direct melt spinning. The effects of a single addition of V and a combined addition of V and C on the structures and magnetic properties of melt-spun Pr8Fe86VB6−xCx (x=0 and 1) ribbons have been investigated. Compared with addition-free ribbons, 1 at% V addition is found to reduce the grain sizes of the samples and improve their magnetic properties due to a strong exchange coupling between the hard and the soft phase. A remanence ratio of 0.82, a coercive field of 6.2 kOe and a maximum energy product of 23.4 MGOe in melt-spun Pr8Fe85VB6 ribbons are obtained at room temperature. The combined addition of V and C is found to lead to the formation of an intermediate phase of VC at grain boundaries, which appears as a pinning barrier during magnetization and results in an increase of the coercivity value to 6.9 kOe for melt-spun Pr8Fe85VB5C ribbons. 相似文献
128.
本文提出了一种开放式磁共振成像(MRI)超导磁体的设计方法.在对磁体模型进行简化的基础上获得初始的电流分布,然后将线圈截面的优化问题转化成一个非线性最小二乘问题,通过求解最小二乘问题得到实际的线圈截面参数.文章最后给出了一个设计算例. 相似文献
129.
根据磁约束等离子体推进器磁体系统的设计参数,通过ANSYS有限元分析软件在电磁-结构耦合场方面的计算,得到磁体系统的轴向电磁力和机械应力的分布。计算超导磁体在通电情况下,磁体中平面上所有节点所受的轴向电磁压缩力以及磁体间的相互作用力;计算出磁体外层用不锈钢钢丝加固前后机械应力分布情况的变化。 相似文献
130.
采用孪生ZnO (Al2 O3 ∶2 % )对靶直流磁控溅射制备高透过率、高电导率的平面ZnO薄膜 (迁移率为 5 .5 6cm2 /V·s,载流子浓度为 4 .5 7× 10 2 0 cm-3 ,电阻率为 2 .4 6× 10 -3 Ω·cm ,可见光范围 (380~ 80 0nm)平均透过率大于 85 % )。用酸腐蚀的方法 ,可以获得绒面效果 ,而反应气压对绒面效果没有影响 ,薄膜的电学特性没有变化 ,绒面对光散射作用增强 ,导致相对于平面ZnO薄膜的透过率要低一些 (可见光范围平均透过率大于 80 % )。 相似文献