均匀磁化介质椭球的退磁因子及退磁场

在椭球坐标系中求解了均匀椭球磁介质在匀强磁场中的磁化问题,得到了空间磁标势、磁场、介质中退磁场和退磁因子的表达式,研究了椭球形状与退磁因子的关系,分析了介质磁化率对退磁场方向的影响.结论为:椭球磁介质内的退磁场是匀强磁场;退磁因子的大小与椭球形状有关,与椭球大小无关,沿椭球长轴方向的退磁因子较小;一般而言退磁场方向与外磁场方向既不相同也不相反.铁磁质椭球内的退磁场几乎与外磁场反向.     

The role of demagnetization factor in determining the ‘true’ value of the Curie temperature

The Curie temperature, T_C, is the temperature above which a material loses its long-range ferromagnetic order. Considering the equation of state of a ferromagnet in the mean-field approximation it has been shown theoretically that the value of the demagnetization factor N has a significant influence on the perceived location of T_C on the temperature scale. A series of precise measurements of magnetization using two differently shaped single crystals of high-purity gadolinium was carried out to prove this result experimentally and develop a procedure leading to the ‘true’ value of T_C.     

The frequency dependence of demagnetizing factor of a Fe-based amorphous ribbon

The frequency dependence of total and internal demagnetizing factors has been investigated. A minimum of the demagnetizing factor at optimal frequency of magnetization reversal is revealed. The influence of the demagnetizing factor on the frequency dependence of magnetic properties of amorphous ribbon is studied.     

The relation between the inner demagnetizing factor of manganese magnesium ferrites and their porosity and permeability

It is shown that the simple relation of direct proportionality between the inner demagnetizing factor and the relative volume of the pores is not sufficient to explain the experimental data obtained on a system of manganese magnesium ferrites. An equation is derived in which the inner demagnetizing factor is directly proportional to the ratio of the relative volume of the pores to the permeability of the sample. The values calculated according to this equation agree well with the experimental results.

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多偏振控制高双折射光纤环形镜输出特性的理论和实验研究

针对光纤环形镜(FLM)在单偏振控制下波长间隔不可调等缺点,对多偏振控制FLM的输出特性进行了理论和实验研究. 用Jones矩阵法分析了单偏振、双偏振和三偏振控制FLM的透射谱,研究发现: 相比单偏振控制FLM,多偏振控制FLM具有波长间隔可调和边频抑制等特性;透射谱的偏振可调性随偏振控制级数的增加而增强,实验结果与理论研究一致. 实验中利用双偏振控制FLM作为波长选择的光纤激光器输出激光的边模抑制比较采用单偏振控制FLM时提高了近5 dB. 关键词： 光纤光学 光纤环形镜 偏振控制 边频抑制     

光纤光栅对FBG-ECL静态特性的影响

光纤光栅外腔半导体激光器(FBG-ECL)在未来光通信系统占有着越来越重要的地位。根据FBG-ECL的等效腔模型,讨论了光纤光栅反射率、带宽对FBG-ECL的输出功率,阈值特性、边模抑制比等静态特性的影响。指出了存在最佳光纤光栅峰值反射率,不仅使得FBG-ECL具有更高的输出功率,而且可以获得极好的边模抑制比。最后根据实测在不同反射率下外腔激光器的激射光谱,发现理论分析结果和实验数据是吻合的。     

Experimental method for determining the total demagnetizing factor of thin amorphous ribbons

The basis of the method is the influence of the demagnetizing field on the maximum rate of magnetic flux change of the amorphous ribbon. The method allows to determine the demagnetizing factor of thin amorphous ribbons in a wide range of its values. With the proposed method the frequency dependence of the demagnetizing factor of amorphous ribbon with a helical magnetic anisotropy was found out.     

Influence of the demagnetizing factor on the magnetization of an ensemble of Stoner-Wohlfarth particles

The influence of the demagnetizing factor on the coercivity of a sample of oriented uniaxial Stoner-Wohlfarth particles is investigated in the approximation of a relaxation model with a self-consistent determination of the demagnetization field. The demagnetizing field is shown to change the particle magnetization reversal conditions and to reduce the blocking temperature and coercivity, for which, despite allowance for the demagnetizing field, the Neel-Brown relation holds. It is also shown that under the demagnetizing field, the internal magnetic field in which the particles are located is not stationary but varies with time concordantly with the time sweep of the temperature during magnetization in a constant external field after zero-field cooling (ZFC). Nonstationarity of the internal field in the ZFC regime causes the interval of transition temperatures of the ensemble particles from a blocked state to a state with equilibrium magnetization to increase.     

Investigation of the static and dynamic magnetic properties of CoFe2O4 nanoparticles

We have investigated the magnetic behavior of cobalt ferrite nanoparticles with a mean diameter of 7.2 nm. AC susceptibility of colloidal cobalt ferrite nanoparticles was measured as a function of temperature T from 2 to 300 K under zero external DC field for frequencies ranging from f=10 to 10,000 Hz. A prominent peak appears in both χ′ and χ″ as a function of T. The peak temperature T₂ of χ″ depends on f following the Vogel–Fulcher law. The particles show superparamagnetic behavior at room temperature, with transition to a blocked state at T_B^m94 K in ZFC and 119 K in AC susceptibility measurements, respectively, which depends on the applied field. The saturation magnetization and the coercivity measured at 4.2 K are 27.3 emu/g and 14.7 kOe, respectively. The particle size distribution was determined by fitting a magnetization curve obtained at 295 K assuming a log-normal size distribution. The interparticle interactions are found to influence the energy barriers yielding an enhancement of the estimated magnetic anisotropy, K=6×10⁶ erg/cm³. Mössbauer spectra obtained at higher temperatures show a gradual collapse of the magnetic hyperfine splitting typical for superparamagnetic relaxation. At 4.2 K, the Mössbauer spectrum was fitted with two magnetic subspectra with internal fields H_int of 490, 470 and 515 kOe, corresponding to Fe³⁺ ions in A and B sites.     

The demagnetizing field on the surface of disc-shaped ferromagnetic samples

The local demagnetizing fields on the surface of flat cylindrical samples (disc) are measured by means of the free radical electron paramagnetic resonance for several thickness-to-diameter ratios from 0·01 to 0·15 and at two values of the external magnetic field (around 4 and 14 kOe). An empirical expression for the demagnetizing field intensity is found and anisotropy of the demagnetizing field is detected in the sample plane. The experimental results are compared with the conclusions of the theory of Joseph and Schlömann.We would like to thank to Mrs J.Smolíková for her help with the evaluation of the results and to Drs. R.Gemperle and V.Kamberský for many valuable suggestions to this problem.     

软X射线条纹相机的静态性能研究

软X光扫描相机是对软X光时间持性进行研究的主要诊断工具,我们利用 同步辐射作为光源,对它的静态性能：能量响应、增益等性能进行了相对标定,给出了软X 光条纹相机的能量响应曲线和增益特性曲线,并与利用B.L.Henke的经验公式计算给出的响 应曲线比较,其结果与理论较符合。     

The static Debye-Waller factor of defect-induced lattice displacements

The attenuation of Bragg scattering intensities due to static displacements is discussed for interstitially dissolved point-defects. It is shown that in the single defect approximation the static Debye-Waller factor (DWF) exp (–2L) decreases linearly with the defect concentrationc and quadratically with the scattering-vectorK (for smallK andc). From a model calculation of the displacements around H in Nb the static DWF is shown to be primarily due to the displacements closest to the impurity. Therefore the measurement of the static DWF can be used as a method to determine these displacements. From X-ray measurements of the integrated Bragg intensities of NbH _x single crystals we obtained the displacements of the four nearest neighbours around a tetrahedral interstitial site to beu ₁=0.1Å. This is in good agreement with the results of our model calculation.     

The fluxgate ring-core demagnetization field

The local demagnetization factor for the ring-core flux gate is derived analytically, based on a tangential magnetization model. The results are in good agreement with experimental data for a wide range of ring shape parameters. Approximate expressions in the limit of a narrow, thin ring are obtained, and indicate that the local demagnetization factor scales with the ratio of the cross-sectional area to the total area of the ring. Analytical modeling of the demagnetization factors for a uniform magnetization state results in an underestimate of the local cross-section averaged demagnetization factors by 50% or more.     

The dependence of the rectangular hysteresis loop on the external stress in manganese-magnesium and manganese ferrites

The dependence of the shape of the hysteresis loop on the external stress was studied on samples of manganese-magnesium and manganese ferrites. A high value was assumed for the energy of the magnetocrystallic anisotropy of manganese-magnesium ferrites of different composition. The sign of the magnetostriction was determined from the character of the changes inB _r/B_m of the samples.The work was done in 1960 at the Institute of Solid State Physics, Prague.The above results are taken from work on the author's graduate thesis which was done in 1960 in the Institute of Solid State Physics. The author thanks Professor J. Bro, Dr. S. Krupika and other members of the magnetic department of the above institute for valuable remarks.     

The nano loop antenna with Fano resonance and symmetrical formation and reconfigurable characteristic for bio-sensing application

Optical and Quantum Electronics - In the present study, ZnO thin films are prepared successfully by simple and flexible spray pyrolysis technique on fluorine doped tin oxide glass substrate. The...     

等离子体激励器的静特性与高速特性仿真研究

将实验测得的电弧放电能量分布规律拟合为理想热源,采用数值仿真方法对一种高频等离子体射流激励器进行参数化研究,探索了激励器出口角度对激励器静特性的影响,并获得了在超声速来流(Ma0=2.0)情况下射流激励器的高速特性。结果显示:当射流出口流通面积相同时射流出口角度越小,激励器沿流向的动量注入能力越强,并且这一规律在高速射流条件的情况下仍然适用。相比静止条件,在超声速来流条件下,射流的动量注入能力更强,影响域更大。     

Fluxmetric and magnetometric demagnetizing factors for cylinders

Fluxmetric and magnetometric demagnetizing factors, _Nf$N_{\mathrm{f}}$ and _Nm$N_{\mathrm{m}}$, for cylinders along the axial direction are numerically calculated as functions of material susceptibility χ$\chi$ and the ratio γ$\gamma$ of length to diameter. The results have an accuracy better than 0.1% with respect to min(_Nf,m,1-_Nf,m)$\min (N_{\mathrm{f},\mathrm{m}},1-N_{\mathrm{f},\mathrm{m}})$ and are tabulated in the range of 0.01?γ?500$0.01?\gamma ?500$ and -1?χ<∞$-1?\chi <\infty$. _Nm$N_{\mathrm{m}}$ along the radial direction is evaluated with a lower accuracy from _Nm$N_{\mathrm{m}}$ along the axis and tabulated in the range of 0.01?γ?1$0.01?\gamma ?1$ and -1?χ<∞$-1?\chi <\infty$. Some previous results are discussed and several applications are explained based on the new results.