Angular dependence of the photothermally modulated magnetic resonance in Gd thin films

In this paper we use electron spin resonance and photothermally modulated magnetic resonance techniques to investigate gadolinium thin films as a function of the orientation of the film surface with respect to the external magnetic field and of the temperature, around the magnetic phase transition temperature. We observe that, in the ferromagnetic phase, the resonance line is shifted up to higher external magnetic fields when the angle between the film surface and the field increases, revealing the magnetic anisotropy of the sample. At the same time, when the temperature is augmented to values higher than the phase transition temperature, the external field of the resonance collapses back to the expected value in the paramagnetic phase for all orientations. We also demonstrated that, even for the perpendicular orientation (magnetic field perpendicular to the sample surface), the photothermally modulated magnetic resonance signal is maximized near the magnetic phase transition temperature. Furthermore, in the ferromagnetic phase the photothermally modulated magnetic resonance intensity is very sensitive to the orientation, showing a significant enhancement in the perpendicular direction.     

外加磁场对射频磁控溅射制备铝掺杂氧化锌薄膜影响的研究

利用射频磁控溅射法制备了铝掺杂氧化锌(AZO)透明导电薄膜,在传统的磁控溅射系统中引入外加磁场,研究了外加磁场对AZO薄膜沉积速率、形貌结构及光电特性的影响.研究结果表明,外加磁场后薄膜的沉积速率从不加磁场的13.04 nm/min提高到了19.93 nm/min;外加磁场后薄膜表面平整致密、颗粒大小均匀,结晶质量较高,而不加磁场薄膜表面形貌呈蠕虫状,薄膜质量较差.溅射时间为90 min时,外加磁场前后AZO薄膜方阻分别为30.74?/和12.88?/.外加磁场对薄膜可见光透过率影响不大,但使薄膜的吸收边蓝移现象更明显.运用ansys软件对磁控溅射二维磁场分布模拟后发现,外加磁场提高了靶上方横向磁场强度,改善了磁场分布的均匀性,加强了磁场对电子的磁控作用,提高了靶电流,是AZO薄膜的溅射速率、光电性能和形貌结构得到提高和优化的原因.     

垂直场下磁性薄膜中的铁磁共振现象

将铁磁共振频率看成外磁场的函数, 讨论了垂直场下磁性膜中的铁磁共振现象. 结果显示: 当外磁场平行于膜面, 并考虑磁膜具有垂直磁晶各向异性情形时, 其磁共振频率随外磁场的变化分为高频支和低频支两种情况, 具体的依赖关系取决于磁膜内磁晶的各向异性; 当外磁场垂直于膜面, 其磁共振频率随外磁场的关系仅存在一支, 一般地, 磁共振频率随外磁场的增加单调地非线性减小, 但当立方磁晶各向异性场H_k1 与单轴磁晶各向异性场H_a之比值介于2/3 < H_k1/H_a <1时, 其磁共振频率随外磁场的增加单调增加, 这与相关的实验结果一致. 研究结果表明: 磁薄膜中有无垂直于膜面的磁各向异性可以通过其磁共振谱的测量进行辨析.     

样品电流模式下外磁场引起的X射线吸收谱强度变化

在用样品电流模式的测量过程中发现，磁场强度、磁场与样品表面的夹角以及光斑在样品表面的位置都会对吸收谱强度产生影响；在光斑、磁场和样品的不同几何配置下,测量并分析了表面均匀氧化的铝箔中氧的K边吸收谱，指出外磁场下吸收谱强度随各种条件变化的趋势，并对实验结果给出了合理解释；结果表明所用的模型分析与实验数据符合得很好；所得到的信息对于XMCD实验的设计安排、相应数据的分析以及物理信息的提取具有重要意义.     

Spin-wave theory for the dynamics induced by direct currents in magnetic multilayers

A spin-wave theory is presented for the magnetization dynamics in a ferromagnetic film that is traversed by spin-polarized carriers at high direct-current densities. It is shown that nonlinear effects due to four-magnon interactions arising from dipolar and surface anisotropy energies limit the growth of the driven spin wave and produce shifts in the microwave frequency oscillations. The theory explains quantitatively recent experimental results in nanometric point contacts onto magnetic multilayers showing downward frequency shifts (redshifts) with increasing current, if the external field is on the film plane, and upward shifts (blueshifts), if the field is perpendicular to the film.     

A simple method to estimate the magnetic moment of magnetic micro-particles

Micro-particles in suspension in a fluid are an example of a very low Reynolds number problem. In this case, no inertial effects are observed. Magnetic micro-particles with magnetic moment m, suspended in a fluid orient to applied external magnetic fields B due to the interaction between the field and the magnetic moment. In this work, we present a simple method to estimate the total magnetic moment of magnetic micro-organisms. The method is based on the application of an external oscillating magnetic field in the sites where the micro-organisms are. In this case, it is possible to obtain theoretically the solution of the equation of motion (rotation of the organism and its trajectory). The solution is a transcendental equation relating the orientation angle and m and can be solved by numerical methods. Changing the frequency and/or the field intensity, it is possible to obtain a situation in which the crystal rotates uninterruptedly (a resonance regime). This condition is related to the applied field intensity, to the frequency, to the medium viscosity, to the crystal dimension, and to the micro-crystal magnetic moment m. The method can be used to estimate the total cellular magnetic moment of magnetic micro-particles.     

The effects of static magnetic field on microwave absorption of hydrogen plasma in carbon nanotubes: A numerical study

We theoretically investigate the microwave absorption properties of hydrogen plasma in iron-catalyzed highpressure disproportionation-grown carbon nanotubes under an external static magnetic field in the frequency range 0.3 GHz to 30 GHz, using the Maxwell equations in conjunction with a general expression for the effective complex permittivity of magnetized plasma known as the Appleton–Hartree formula. The effects of the external static magnetic field intensity and the incident microwave propagation direction on the microwave absorption of hydrogen plasma in CNTs are studied in detail. The numerical results indicate that the microwave absorption properties of hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes can be obviously improved when the external static magnetic field is applied to the material. It is found that the specified frequency microwave can be strongly absorbed by the hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes over a wide range of incidence angles by adjusting the external magnetic field intensity and the parameters of the hydrogen plasma.     

Enhancement of nonlinear properties of superconducting films in low-frequency magnetic field

The effect of enhancement of nonlinear properties of superconducting films is found in low-frequency magnetic field. Harmonic mixing of the electromagnetic radiation is detected. These results provide an argument in support of a new approach to design the active superconducting elements. A low-frequency oscillating magnetic field directed perpendicularly to the film surface forms an unstable vortex structure in the film. The frequency multiplication is intensified in the vortex unstable state. A transition of the vortex structure into the ground state synchronized by an external resonant circuit causes the generation of the electromagnetic radiation. Main advantage of these oscillators over Josephson junctions is high power emitted into a broadband system.     

Specific features of chemisorption on a size-quantized film in an external quantizing magnetic field

The energy of an electron of an adatom chemisorbed on a size-quantized film is investigated as a function of the external quantizing magnetic field. Consideration is given to the cases when the external magnetic field is directed parallel and transverse to the film surface. It is demonstrated that, as the magnetic field increases, the energy of chemisorption jumpwise decreases.     

Refraction of surface spin waves in spatially inhomogeneous ferrodielectrics with biaxial magnetic anisotropy

The refractive index of surface spin waves propagating in a ferromagnetic medium with a nonuniform distribution of the parameters of uniaxial and orthorhombic magnetic anisotropies and exchange coupling is determined within the spin-density formalism. The coefficients of reflection and transmission of spin waves at the interface between two homogeneous magnets with different constants of uniaxial and orthorhombic magnetic anisotropies, exchange coupling, and saturation magnetization are calculated. The dependences of the intensity of a reflected wave and the refractive index on the wave frequency and the strength of an external dc homogeneous magnetic field are determined.     

Magneto-optic fiber Sagnac modulator based on magnetic fluids

A magneto-optic modulator with a magnetic fluid film inserted into an optical fiber Sagnac interferometer is proposed. The magnetic fluid exhibits variable birefringence and Faraday effect under external magnetic field that will lead to a phase difference and polarization state rotation in the Sagnac interferometer. As a result, the intensity of the output light is modulated under the external magnetic field. Moreover, the modulator has a high extinction ratio and can easily be integrated in a single-mode fiber system. The performance of the modulator is not affected by ambient temperature variation from room temperature to 40 °C.     

The dynamic behavior of magnetic fluid adsorbed to small permanent magnet in alternating magnetic field

The dynamic behavior of a magnetic fluid adsorbed to a small NdFeB permanent magnet subjected to an alternating magnetic field was studied with a high speed video camera system. The directions of alternating magnetic field are parallel and opposite to that of the permanent magnet. It was found that the surface of magnetic fluid responds to the external alternating magnetic field in elongation and contraction with a lot of spikes. Generation of a capillary magnetic fluid jet was observed in the neighbourhood of a specific frequency of alternating field. The effect of gravitational force on surface phenomena of magnetic fluid adsorbed to the permanent magnet was revealed.     

Tunable diffraction of magnetic fluid films and its potential application in coarse wavelength-division multiplexing

When an external magnetic field is applied parallel to the film surface of a magnetic fluid film, a high-quality one-dimensional periodic chain structure is formed when the field strength reaches a certain level. With a periodic chain structure in the magnetic fluid film, an incident light is diffracted onto the magnetic thin film. The results show that the one-dimensional periodic chain structure in the magnetic fluid film can serve as an optical grating. Further investigations reveal the feasibility of developing tunable coarse wavelength-division multiplexing by utilizing a periodic chain structure.     

Calculation of electric and magnetic induced fields in humans subjected to electric power lines

In this work, analysis of the human body exposed to high voltage electric and magnetic fields is presented. The distribution of the electric field is obtained by using Laplace's equation. This relates the surface charge induced on the body to the potential in a reciprocal Laplace problem, which is then calculated by charge simulation method coupled with genetic algorithms to determine the appropriate arrangement of simulating charges inside the human body. The magnetic field intensity along the vertical center line of the human is calculated. Exposure to external electric and magnetic fields at power frequency induces electric field, magnetic field and currents inside the human body. The presented model for simulating electric and magnetic fields are a three dimensional field problem and introduced different types of charges to simulate the different elementary geometrical shapes of human body. The particular strength of the charge simulation method in this application is its ability to allow a detailed representation of the shape and posture of the human body. The results have been assessed through comparison induced current, electric field, magnetic field and there distribution over the body surface, as estimated in other experimental and computational work.     

Tuning the optical transmission through a homogeneous doped semiconductor film by applying an external magnetic field

We theoretically and numerically studied the transmission of light through a homogeneous doped semiconductor film with a Drude tensor in the presence of an external magnetic field. The magneto-induced homogeneous metal films are found to exhibit a magneto-induced light transparency due to cyclotron resonance. In particular, the surface plasmon (SP) resonance mode of the magneto-induced metal film move to higher frequencies with increasing magnetic field, bringing about large changes in the extraordinary light transmission peaks predicted to occur in such a magneto-induced semiconductor film.     

Domain structure in magnetic films with a saturation magnetization higher than the anisotropy field

The domain structure (DS) of yttrium-iron garnet films with uniaxial anisotropy fields higher than ∼120 Oe was found to have a 3D character: there is a stripe domain structure of a certain type in the surface layer and a structure of another type in the film bulk. It was revealed that in the absence of an external magnetic field, the boundaries of both DSs are almost perpendicular, whereas with an increase in an external field applied in the film plane along the boundaries of the interior-volume DS, the boundaries of the surface DS are gradually reoriented along the external field. This phenomenon is theoretically explained on the basis of the micromagnetic model, which describes DS formation in ferrite films.     

磁化等离子体环境对氢原子能级结构的影响

本文通过非微扰求解薛定谔方程, 研究了强磁场磁化的等离子体环境中的原子能级结构和辐射动力学过程. 在较宽的磁场强度范围和等离子体屏蔽参数范围内, 给出了氢原子基态以及低激发态的能级、辐射跃迁能量和振子强度等重要的原子参数, 定量地描述了强磁场和等离子体屏蔽共同作用的综合效应. 相关的结果有助于增进对极端环境下原子光谱结构的认识, 在等离子体光谱诊断和天文光谱观测方面有一定的借鉴意义. 关键词： 强磁场 CWDVR谱方法 能级结构 振子强度     

Effect of external magnetic field on the shift of resonant frequency in photoassociation of ultracold Cs atoms

We study the influence of external magnetic field on the shift of the resonant frequency in the photoassociation of ultracold Cs atoms, which are captured in a magnetically levitated optical crossed dipole trap. With the increase of the photoassociation laser intensity, the linear variation of the frequency shift is measured by recording the photoassociation spectra of the long-range 0_u~+ state of Cs molecule below the 6S_(1/2)+ 6P_(1/2) dissociation limit at different magnetic fields.The slope of the frequency shift to the intensity of the photoassociation laser exhibits a strong dependence on the external magnetic field. The experimental data is simulated with an analytic theory model, in which a single channel rectangular potential with the tunable well depth is introduced to acquire the influence of the magnetic field on the atomic behavior in the effective range where photoassociation occurs.     

Transmission through a perforated metal film by applying an external magnetic field

We theoretically and numerically studied the transmission of light through a subwavelength-perforated metal film in the presence of an external magnetic field. The perforated metal films are found to exhibit a magnetoinduced light transparency due to cyclotron resonance. The localized waveguide surface plasmon (SP) resonance mode and periodicity-structure-factor-induced SP resonance mode are discussed by application of a static magnetic field. The field distributions are localized separately on the left and right metal-air surfaces for structure-factor-induced resonance mode. And for localized cavities resonance mode, standing electromagnetic fields can also be entirely localized inside the nanohole region.     

Dynamic magnetic susceptibility of a two-layer film in a strong magnetic field

A theoretical study is reported of the effect of interlayer exchange coupling on the resonance properties of a two-layer magnetic film with “easy-axis” and “easy-plane” anisotropic layers in a strong tilted magnetic field. The dependence of the resonance fields on the tilting angle of the external magnetic field to the film has been obtained, the tensor of integrated high-frequency film susceptibility has been found, and its dependence on the strength and orientation of the external field, as well as on layer thickness, has been analyzed. The results obtained agree with the available experimental data.