共查询到20条相似文献,搜索用时 15 毫秒
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Technical Physics Letters - We present results of an experimental investigation of the transition to a microwave dynamic chaos regime in ring oscillators based on normally magnetized yttrium iron... 相似文献
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Various applications of the Faraday and Kerr effects for the investigation of domain structures and reversal mechanisms in thin ferromagnetic films are reviewed. Different optical arrangements for the observation of domains are described and compared. Using magnetooptic microscopy domains and wall structures can be observed with a resolution of 1 μm. Magnetization structures give rise to diffraction phenomena, which are revealed as Fresnel fringes, Fraunhofer patterns, and dark field pictures. Applications of these phenomena and the consequences for the resolution of magneto-optic microscopy are discussed. Various kinds of reversal processes by wall motion or rotation, respectively, can be distinguished from each other by measuring the light intensity in two settings of the analyzer and by a dark field method. These reversal mechanisms can be identified even in case of fast switching when direct observations are not possible. Since the applications of magnetooptics are not restricted by any temperature limit, they are especially suited for the investigation of temperature dependent phenomena, e.g., the Barkhausen effect and the magnetic aftereffect. A picture of a domain structure in a gadolinium film at 80°K is shown. 相似文献
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E. N. Beginin S. V. Grishin M. A. Morozova Yu. P. Sharaevskii 《Technical Physics Letters》2009,35(9):853-856
Various regimes of chaotic signal generation have been studied in an self-oscillating ring system with a wideband nonlinear
delay line based on coupled ferromagnetic films, in which magnetostatic backward volume waves (MSBVWs) are excited. It is
shown for the first time that the simultaneous excitation of two waves in the coupled films leads to the appearance of a falling
part in the dynamic characteristic of the MSBVW delay line and the generation of a broadband chaotic signal with a continuous
spectrum. Under certain conditions, the ring exhibits a regime of intermittency, in which broadband chaotic signals with both
continuous and discrete spectra are generated. 相似文献
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The enhancement of the Kerr magneto-optic effect by overcoating a ferromagnetic film with a dielectric film is studied. It is treated as an impedance-matching problem for the light wave. Closed form solutions are obtained for the polar Kerr effect. The same analysis, with modifications, can be applied to the longitudinal Kerr effect. The effect of the dielectric thickness on the enhancement is continuously monitored with a laser beam (λ = 6328Å) during the dielectric film deposition. The amplification of the longitudinal Kerr signal with SiO films on iron film is of the order of five, and the enhancement varies periodically as a function of dielectric thickness. The experimentally observed period, 1600Å, agrees well with the calculated value. The sense ofB-H loops, which also varies periodically as a function of the dielectric thickness, is explainable in terms of the phase factor which appears in the difference between the reflection coefficients. 相似文献
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The present status of the theory of saturation magnetization of ferromagnetic thin films is reviewed. The extensions of the Heisenberg trace method and the spin-wave method to the case of ferromagnetic thin films is fully discussed together with a comparison of the theoretical results with experimental data. The effect of anisotropic magnetic fields on magnetization and Curie temperature is presented, and the dependence of the magnetization and Curie temperature on film thickness is studied. Very recent progress and new results of the theory are stressed. The application of the Green function method to ferromagnetic thin films is also examined. 相似文献
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We induce a microwave photonic bandpass filter into an optoelectronic oscillator to generate a chaotic ultra-wideband signal in both the optical and electrical domain. The theoretical analysis and numerical simulation indicate that this system is capable of generating band-limited high-dimensional chaos. Experimental results coincide well with the theoretical prediction and show that the power spectrum of the generated chaotic signal basically meets the Federal Communications Commission indoor mask. The generated chaotic carrier is further intensity modulated by a 10 MHz square wave, and the waveform of the output ultra-wideband signal is measured for demonstrating the chaotic on-off keying modulation. 相似文献
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Wen-Yin KoJun-Wei Su Chian-Hua GuoShu-Juan Fu Chuen-Yuan HsuKuan-Jiuh Lin 《Thin solid films》2011,519(22):7717-7722
Open rings of multi-walled carbon nanotubes were stacked to form porous networks on a poly(ethylene terephthalate) substrate to form a flexible conducting film (MWCNT-PET) with good electrical conductivity and transparency by a combination of ultrasonic atomization and spin-coating technique. To enhance the electric flexibility, we spin-coated a cast film of poly(vinyl alcohol) onto the MWCNT-PET substrate, which then underwent a thermo-compression process. Field-emission scanning electron microscopy of the cross-sectional morphology illustrates that the film has a robust network with a thickness of ~ 175 nm, and it remarkably exhibits a sheet resistance of approximately 370 Ω/sq with ~ 77% transmittance at 550 nm even after 500 bending cycles. This electrical conductivity is much superior to that of other MWCNT-based transparent flexible films. 相似文献
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Static wall coercive force in ferromagnetic thin films 总被引:1,自引:0,他引:1
The static wall coercive force of thin ferromagnetic films has been calculated from a model of conservative wall energy. The spatial dependence of the wall energy γw is assumed to be given by the mean value of the local anisotropy energy, averaged over a coupling volume of the wall. The result of the calculation shows thatH_{w} propto frac{S}{M_{s}} (frac{D}{W})^{1/2} frac{1}{L} where the structure constantS includes the local anisotropy,D is the mean diameter of a region with constant anisotropy (for instance crystallites),W is the wall width; andL is the coupling length parallel to the wall. 相似文献
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Collinear ferromagnetic spin ordering in a thin film with pinned surface spins is shown to be stable only for certain orientations of the magnetisation vector. Also, the magnon potential is shown to extend outward from the film surface; according to whether the surface spins are pinned more strongly or less strongly than the internal spins, the potential becomes infinite at a distance outward from the surface smaller or larger than one lattice constant. 相似文献
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在铁磁性元素中,交换能、偶极能和各向异性能之间存在复杂的竞争,因此,这种结构化介质的静态和动态性能与构成材料的固有磁特性,各个元素的形状和尺寸等有着密切的关系.这些多个自由度提供了对于通常未构图的磁性薄膜不可达到的新性能.本文通过将所研究的系统划分成立方体网格的三维阵列来对其进行建模,研究具有不同相对位置、纳米片间距、磁各向异性方向的两矩形铁磁性纳米片的微波磁性能.研究发现:与单个矩形铁磁性纳米片相比,具有不同相对位置、纳米片间距的两矩形铁磁性纳米片共振峰频率分布发生变化;当两矩形纳米片磁各向异性方向所呈角度由0°增加到30°时,其磁性质没有明显变化,而从30°到90°时,其磁性质对磁各向异性方向变化比较敏感.通过调控纳米片的相对位置、纳米片间距以及磁各向异性方向可以制备具有良好性能的吸收材料. 相似文献
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B.B. Straumal A.A. Mazilkin S.G. Protasova A.A. MyatievP.B. Straumal E. GoeringB. Baretzky 《Thin solid films》2011,520(4):1192-1194
Pure ZnO thin films were obtained by the wet chemistry (“liquid ceramics”) method from the butanoate precursors. Films consist of dense equiaxial nanograins and reveal ferromagnetic behaviour. The structure of the ZnO films was studied by the high-resolution transmission electron microscopy. The intergranular regions in the nanograined ZnO films obtained by the “liquid ceramics” method are amorphous. It looks like fine areas of the second amorphous phase which wets (covers) some of the ZnO/ZnO grain boundaries. Most probably these amorphous intergranular regions contain the defects which are responsible for the ferromagnetic behaviour. 相似文献
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We find a direct correspondence between the lattice mismatch and the in-plane angular dependence of the FMR field for epitaxial YIG films on non-magnetic garnet substrates. 相似文献
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Hailing Yang Xiaoguang Xu Xiaoye Zhou Yannan Ma Jing Dong Tianqi Wang Jun Miao Yong Jiang 《Journal of Materials Science》2012,47(18):6513-6516
Boron-doped ZnO films were prepared by pulsed laser deposition technique. Magnetic, electrical, and optical properties of Zn1?x B x O films have been studied. It is found that the magnetic properties of the Zn1?x B x O films are sensitive to growth oxygen partial pressure. The films deposited under a high oxygen partial pressure of about 10?Pa appear to be ferromagnetic insulators at room temperature (RT). However, when the oxygen partial pressure decreases to 1.2?Pa, the films are non-ferromagnetic conductors at RT. Zn vacancies, which can be controlled by the oxygen partial pressure, are shown to be essential for realizing ferromagnetism (FM); on the other hand, the n-type nature of ZnO has no contribution to the FM observed in the B-doped ZnO films. 相似文献
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Using a general scattering matrix approach in the theoretical analysis the polar Kerr rotation is shown to have a marked dependence on sample thickness when the thickness is less than 60 nm. The polar Kerr rotation is calculated for thin films of iron and cobalt for normal incidence in the wavelength range 400–1400 nm for both unbloomed and bloomed specimens. 相似文献
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Horst Hoffmann 《Thin solid films》1979,58(2):223-233
The influence of film structure on magnetic properties is primarily due to the creation of spatially fluctuating local anisotropies which make the magnetization direction inhomogeneous. The deviation from homogeneous magnetization of domains, the so-called ripple, influences a great number of static, quasistatic and dynamic effects via the intrinsic demagnetizing field. The ripple theory is expressed in terms of only one phenomenological constant, the structure constant S, which covers completely the influence of the film structure on the deviations of real thin film behaviour from that of ideal single domains. 相似文献