Scratch-modified magnetic domain patterns in garnet films

If a loaded Al₂O₃ sphere is passed over SmGa and LuTb garnet crystalline films, the domain pattern is modified. The width of the changed pattern is proportional to the diameter of the zone of contact between the sphere and the garnet. The pattern depends on load: a herring-bone type is found at low loads, a parallel pattern at high loads. After a magnetic field has disturbed the pattern, a narrow region of straight domains is left, which persists unless the material is heated above 1100°C. The patterns are independent of the sign of the magnetostriction constants.     

Iron-yttrium garnet films with magnetic vortices

Submicron iron-yttrium garnet films have been studied. The effect of the switching of nonreciprocal resonance absorption, which is caused by the switching of the polarization of vortices, has been revealed.     

Domain wall oscillations in magnetic garnet films

Domain wall oscillations in magnetic garnet films have been observed in the stripe lattice and in the bubble lattice for applied in-plane magnetic fields approaching the saturation limit of the film. Observations are reported in (111) and (001) oriented films. An effective domain wall mass model is developed which allows the variation of the azimuthal angle of the spins in a moving wall when an in-plane field is applied in the plane of the wall. The new model gives results which are in much better agreement with the experimental results than previous models. Reasonable agreement is also observed between theory and experiment when the cubic anisotropy is included. Experimental evidence of the Hubert wall structure and its change for in-plane fields less than 8M is also reported.     

Microscopic theory of soliton propagation in4He films

A microscopic theory has been provided for propagation of solitons in superfluid⁴He films at temperatureT=0°K.     

Studies on magnetic photonic band-gap material at microwave frequency

The microwave transmission characteristics of magnetic photonic band-gap (MPBG) materials, in which the periodic structures are composed of alternating layers of polycarbonate with and without ferromagnetic nanowires, are studied. We present a theoretical method to investigate the transmission spectra of the MPBG material. The band-gap effect varies with the periodic parameters of the MPBG structure. Our calculation can describe well the experimental measurement value. The influence of the applied static magnetic field on the MPBG and the ferromagnetic resonance phenomenon has been studied.     

Magnetostatic wave propagation in a double-layered film structure under inclined magnetic field

Under inclined magnetic field, the propagation characteristics of magnetostatic waves (MSWs) for a double-layered waveguided structure are theoretically studied by using surface permeability method. A new concept called ‘mode interlamination coupling’ is proposed by analysis of mode spectrum, which develops a generalized understanding of the MSWs propagating in a layered structure. A similar treatment can be applied to the situation of multi-layered structure under inclined field. In addition, the dispersion relation and delay characteristics of coupled mode in two different YIG films are studied by numerical analogue at inclination angle from 5 to 20°. The results indicate that the MSWs propagating in double-layer structure is appropriate for high frequency range (8.4∼10 GHz) under inclined field, and it has an optimum range of delay rate superior to single film by adjusting the inclination angle of the magnetic field. Apparently, the performances of double-layered film structure under inclined field have potential dominance in channelization and stability of signal processing for the application of magneto-optic waveguided devices in the future.     

Optical measurement of magnetic anisotropy in thin garnet films

This paper describes an improved optical method for measuring locally the cubic and uniaxial magnetic anisotropy fields in thin garnet films. The derivative of the in-plane component of the magnetization is measured, using a double modulation technique which combines polarization modulation with field modulation. A simple graphical method is devised to calculateH _k andH _u from the extrema in this derivative curve. The results of measurements on magnetic garnet films obtained by different methods are compared. Local measurements of the anisotropy induced by substrate facet strain are described.     

High-frequency excitations of stripe-domain lattices in magnetic garnet films

Magnetic garnet films of composition (Y,Bi)₃(Fe,Al)₅O₁₂ have been grown by liquid phase epitaxy on [111] and [110] oriented substrates of gadolinium gallium garnet. The domain wall resonance and the two branches of the domain resonance of periodic stripe domains are measured as function of the bias induction applied in the film plane parallel to the stripes. Resonance frequencies up to 7.5 GHz are observed. An improved version of the hybridization model is developed to describe these resonances. It turns out that hybridization of the domain resonance branches is determined by the cubic anisotropy for [111] oriented films, while for [110] oriented films coupling of the domain resonances is mainly caused by the orthorhombic anisotropy. The theoretical model is in excellent agreement with experiments, no fitting parameters are used. It is also used to derive the phase relation between the precessing magnetizations of neighbouring domains.     

Magnetostatic spin waves in (111)-oriented thin garnet films with combined cubic and uniaxial anisotropies

The magnetostatic spin wave theory in (111)-oriented ferromagnetic films characterized by cubic and uniaxial anisotropies (CUA) is developed. The theory is discussed for two cases when the magnetization vector is perpendicular or parallel to the sample plane. In CUA films, instead of the usually discussed magnetostatic surface waves known for the isotropic case, a new type of surface waves was found with the complex wavevector component normal to the surface.It is shown that for the pure yttrium-iron-garnet film the influence of the CUA effects on the dispersion characteristics of the surface waves is not very substantial.     

Liquid phase epitaxy magnetic garnet films and their applications

Liquid phase epitaxy(LPE) is a mature technology. Early experiments on single magnetic crystal films fabricated by LPE were focused mainly on thick films for microwave and magneto–optical devices. The LPE is an excellent way to make a thick film, low damping magnetic garnet film and high-quality magneto–optical material. Today, the principal challenge in the applied material is to create sub-micrometer devices by using modern photolithography technique. Until now the magnetic garnet films fabricated by LPE still show the best quality even on a nanoscale(about 100 nm), which was considered to be impossible for LPE method.     

Visualization of nonuniform magnetic fields by garnet ferrite films

The magnetization distribution in epitaxial garnet ferrite films subjected to the harmonic field of a signal from a magnetic tape is studied. By means of image processing techniques and diffraction spectrum analysis, it is shown that the distortion of the signal shape grows with increasing amplitude and period of the field.     

Ferrimagnetic resonance spectra of magnetic bubble films at low microwave frequencies

Magnetic bubble films exhibit a number of ferrimagnetic resonance modes due to the spatial variation of the anisotropy. The resonance frequencies have been measured as a function of the applied bias fieldH ₀. In the lower field range the magnetization of the transient layer, which has negative anisotropy, is not yet parallel toH ₀. In this range the resonance frequencies are shifted to higher values due to pinning effects. In films grown by the vertical dipping method an additional layer on top of the transient layer is observed within which the magnetization rotates from the direction in the transient layer to that of the bulk of the film. In films grown by horizontal dipping no such layer could be detected. Each ferrimagnetic resonance mode excites transverse elastic waves in the film due to the magnetoelastic interaction and thus gives rise to elastic resonances of the whole crystal, film and substrate. These elastic resonances lead to a fine-structure of the ferrimagnetic resonances. The observed fine-structure vanishes periodically with frequency and from this behaviour the thickness of the magnetic film and of the transient layer has been determined.     

Observation of the chaotic spin-wave soliton trains in magnetic films

The transition from stationary to chaotic spin-wave soliton trains has been observed. The experiment utilized cw excitation of envelope solitons through self-modulation instability of spin waves. By increasing the spin-wave power, the secondary self-modulation instability succeeded the primary modulation instability, resulting in after-modulation of the soliton train amplitude. Further increase of the spin-wave power led to development of the higher-order instabilities, resulting in formation of the chaotic soliton train.     

Domain-wall dynamics in ferrite garnet films in strong in-plane magnetic fields

The domain-wall dynamics in the ferrite garnet films with the (111) orientation has been investigated by twofold high-speed digital photography in the presence of a magnetic field close in strength to the anisotropy field.     

射频击穿等离子体对高功率微波传输特性的影响

利用极化正交的高功率微波合路器,开展了等离子体对于微波传输特性的实验研究.通过改变前级源的功率和脉冲宽度,使得在合路器耦合缝处发生射频击穿,产生等离子体.等离子体扩散进入微波传输主通道,对于高功率微波的传输产生明显的影响,导致微波能量吸收和极化的偏转.初步实验结果表明,等离子体扩散到主通道中心的时间约为3μs,扩散速度约为1μs/cm,等离子体的恢复时间约为5μs.实验测得等离子体导致的微波极化方向最大偏转角度约为4.1?,此时通道内电子个数约为3.7×1015,极化偏转角度与电子数密度以及微波频率相关.     

Microscopic theory of soliton propagation in a mixture of two boson fluid films

A microscopic theory of soliton propagation in a mixture of two boson fluids atT=0°K has been provided.     

Collisions in dispersion-managed soliton propagation

We study collisions in dispersion-managed soliton propagation for wavelength-division multiplexing application at zero net dispersion when the Gordon-Haus timing jitter is removed. We show that the collisions can lead to group-velocity changes and spectral collapse. Large channel separation ameliorates the effects. Filters prevent spectral collapse but do not affect the velocity changes.     

Experimental evidence of the magnetic moment of Bloch walls in garnet films

Differential susceptibility measurements in low in-plane fields showed up a new peak assumed to be caused by magnetization reversal inside the Bloch walls (BW). Highly sensitive measurements carried out subsequently on different domain structures yielded various new parameters such as the BW hysteresis curve, the integral saturated and remanent BW moments and the internal BW coercivity. The mechanism proposed for the observed phenomena is based on the reversible and irreversible motion of Bloch lines inside the Bloch walls.     

Magnetostatic volume waves in exchange-coupled ferrite films

The influence of exchange coupling of layers on the propagation of magnetostatic dipole volume waves in normally and tangentially magnetized two-layer epitaxial ferrite structures is investigated. It is shown that the indicated influence is manifested in the form of dynamic spin pinning effects on the interlayer boundary and formation of a common dipole-exchange wave spectrum for the entire structure. In this case, at the synchronism frequencies of the dipole and exchange waves the losses of the dipole waves grow and anomalous segments appear in the dispersion. In films magnetized in the “hard” direction relative to the axis of normal uniaxial surface anisotropy the magnetostatic dipole volume waves can interact resonantly with the surface spin waves supported by the boundaries with pinned spins. Zh. Tekh. Fiz. 68, 97–110 (July 1998)     

The 50 nm-thick yttrium iron garnet films with perpendicular magnetic anisotropy

Yttrium iron garnet (YIG) films possessing both perpendicular magnetic anisotropy (PMA) and low damping would serve as ideal candidates for high-speed energy-efficient spintronic and magnonic devices. However, it is still challenging to achieve PMA in YIG films thicker than 20 nm, which is a major bottleneck for their development. In this work, we demonstrate that this problem can be solved by using substrates with moderate lattice mismatch with YIG so as to suppress the excessive strain-induced stress release as increasing the YIG thickness. After carefully optimizing the growth and annealing conditions, we have achieved out-of-plane spontaneous magnetization in YIG films grown on sGGG substrates, even when they are as thick as 50 nm. Furthermore, ferromagnetic resonance and spin pumping induced inverse spin Hall effect measurements further verify the good spin transparency at the surface of our YIG films.