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41.
芘和苯甲醛,在对甲基苯磺酸作用下,生成了B阶COPNA树脂.用红外光谱、核磁共振氢谱及碳谱对其结构进行了表征.B阶COPNA树脂经在惰性气氛中500、600和800℃的热处理后,得到不溶不熔的COPNA树脂.电子自旋共振谱(ESR)测试表明,其稳定自由基浓度最高可达2.28×1022spins/g. 相似文献
42.
As an essential model of magnetoelastic interaction between magnetic field and mechanical deformation, the study on magnetoelastic
buckling phenomenon of soft ferromagnetic plates in a magnetic environment has been conducted. One of the key steps for the
theoretical prediction of the critical magnetic field is how to formulate magnetic force exerted on the magnetized medium.
Till today, the theoretical predictions, from theoretical models in publications, of the magnetoelastic buckling of ferromagnetic
cantilevered beam-plate in transverse magnetic field are all higher than their experimental data. Sometimes, the discrepancy
between them is as high as 100%. In this paper, the macroscope formulation of the magnetic forces is strictly obtained from
the microscope Amperion current model. After that, a new theoretical model is established to describe the magnetoelastic buckling
phenomenon of ferromagnetic thin plates with geometrically nonlinear deformation in a nonuniform transverse magnetic field.
The numerical method for quantitative analysis is employed by combining the finite elemental method for magnetic fields and
the finite difference method for deformation of plates. The numerical results obtained from this new theoretical model show
that the theoretical predictions of critical values of the buckling magnetic field for the ferromagnetic cantilevered beam-plate
are in excellent agreement with their experimental data. By the way, the region of applicability to the Moon-Pao's model,
or the couple model, is checked by quantitative results.
This project was supported in part by the National Natural Science Foundation of China and the Foundation of the SEdC of China
for Returned Chinese Scholars from Abroad. 相似文献
43.
W. Kullmann K. Strobel R. Geick 《International Journal of Infrared and Millimeter Waves》1984,5(9):1251-1268
We have studied ferromagnetic resonance in the millimeter wave range between 35 and 100 GHz with external fields ranging from 1 to 4 T. The results show that it is advantageous to employ quasi-optical methods in this range. Moreover, our results demonstrate also that propagation and polariton effects cannot be neglected in analyzing the spectra. The experiments have been performed on K2CuF4, a transparent quasi-two-dimensional ferromagnet. 相似文献
44.
对"多铁性"脉冲形成线输出特性进行了研究。利用镍锌铁氧体-钛酸钡陶瓷复合多铁性材料制作了脉冲形成线。在不同的磁回路条件下得到了不同脉冲宽度的电脉冲方波,其中以高磁导率材料组合成的闭合磁回路得到了脉冲宽度约201 ns的方波输出。推算出脉冲形成线的相对介电常数接近2 000,相对磁导率大于1.4。基于有效磁导率的概念,分析了多铁性脉冲形成线几何构型对脉冲输出特性的影响。分析表明:平板状"多铁性脉冲形成线"的有效磁导率不仅取决于平板介质的磁导率,还取决于周围介质的磁导率,因而有效磁导率通常较小,其输出表现出明显的铁电性而只有"弱"的铁磁性;相比之下,同轴结构的"多铁性脉冲形成线"具有更高的有效磁导率,其输出可同时表现出强的铁电性和铁磁性,即更明显的"多铁性"。"多铁性脉冲形成线"有可能在紧凑型脉冲功率系统中获得应用。 相似文献
45.
Ekaterina A. Ilyina Carla Cirillo Carmine Attanasio 《Physica C: Superconductivity and its Applications》2010,470(19):877-879
Current–voltage (I–V) characteristics and critical current density, Jc, for the onset of vortex motion were measured at different magnetic fields, H, and temperatures, T, in a superconducting (S)/ferromagnetic (F) bilayer and in a single Nb film. We choose Nb as a superconductor and a weak ferromagnetic alloy, Pd1−xNix with x = 16, as F. We found that Jc was smaller for the S/F bilayer with respect to the single Nb film. The result was related to the reduced value of the superconducting order parameter in the bilayer. 相似文献
46.
本文在一维海森堡模型的基础上,采用界面参数化方法,研究了铁磁/反铁磁双层薄膜中自旋波低温激发问题.重点讨论了表面各向异性对薄膜中自旋波共振谱的影响.结果表明:体系中的自旋波本征模存在共振行为,表面各向异性场对体模、完全禁闭模的共振谱影响较大,对界面模没有影响. 相似文献
47.
Abstract The two-dimensional Heisenberg antiferromagnet (C2H5NH3)2CuCl4 has the ferromagnetic intralayer exchange interaction, while the extremely weak interlayer exchange interaction is antiferromagnetic. Neutron scattering experiments under high pressures have been performed on this compound. We confirm that the spin structure changes around 1~2 GPa from the collinear alignment along the a-axis to a spin-canting one. The weak moment due to the canting is parallel to the c-axis. The results indicate that the ferromagnetic intralayer and the antiferromagnetic interlayer exchange interactions are maintained up to 1~2 GPa. Why the weak ferromagnetic moment along the c-axis occurs is due to a lowering of crystal symmetry by pressure. 相似文献
48.
通过实验和计算的方法研究了Mn2CoMxGa1-x 和Mn2CoMxAl1-x (M=Cr, Fe, Co)掺杂系列合金样品. 研究发现, 在共价作用的影响下, Fe和Co原子占A位, 使被取代的MnA (-2.1 μB)变成MnD (3.2 μB), 在最近邻的强交换作用下亚铁磁基体中形成了MnB-CoC-MnD局域铁磁性结构, 使分子磁矩的增量最高可达6.18 μB. Fe, Co 掺杂后建立同样的局域铁磁结构, 居里温度的变化趋势却不同. 实验观察到Mn2Co1+xAl1-x中掺杂容忍度高达x=0.64, 远高于在Mn2CoGa中(x=0.36)的结果; 以及随着Al的减少, 合金由B2有序向A2混乱转变等现象, 为共价作用对合金结构稳定的影响提供了证据. 磁测量中发现Cr掺杂后磁矩增量高达3.65 μB以及居里温度快速上升的反常现象, 意味着对占位规则的违背. 相似文献
49.
Frank J. Owens 《Molecular physics》2013,111(12):1527-1531
Density functional theory (DFT) employing the local spin density approximation and including correlation functionals is used to show that increasing the boron content relative to the nitrogen content in boron nitride nanoribbons can significantly reduce the band gap making the ribbons semiconducting. Armchair ribbons, but not zigzag ribbons, having excess borons are predicted to have a more stable optimized triplet structure than the optimized singlet structure. The triplet structure is predicted to have a higher density of states at the top of the valence band near Fermi level for the spin down state indicating it could be a ferromagnetic semiconductor. The results suggest a possible new approach to developing ferromagnetic semiconductors. 相似文献
50.
杨森 鲍慧新 周超 王宇 任晓兵 宋晓平 Yoshitaka Matsushita Yoshio Katsuya Masahiko Tanaka Keisuke Kobayashi 《中国物理 B》2013,(4):1-16
Ferromagnetic transition has generally been considered to involve only an ordering of magnetic moment with no change in the host crystal structure or symmetry, as evidenced by a wealth of crystal structure data from conventional X-ray diffractometry (XRD). However, the existence of magnetostriction in all known ferromagnetic systems indicates that the magnetic moment is coupled to the crystal lattice; hence there is a possibility that magnetic ordering may cause a change in crystal structure. With the development of high-resolution synchrotron XRD, more and more magnetic transitions have been found to be accompanied by simultaneous structural changes. In this article, we review our recent progress in understand- ing the structural change at a ferromagnetic transition, including synchrotron XRD evidence of structural changes at the ferromagnetic transition, a phenomenological theory of crystal structure changes accompanying ferromagnetic transitions, new insight into magnetic morphotropic phase boundaries (MPB) and so on. Two intriguing implications of non-centric symmetry in the ferromagnetic phase and the first-order nature of ferromagnetic transition are also discussed here. In short, this review is intended to give a self-consistent and logical account of structural change occurring simultaneously with a ferromagnetic transition, which may provide new insight for developing highly magneto-responsive materials. 相似文献