Spin-wave resonance in multilayer films (one-dimensional magnon crystals). Identification rules

The characteristic modification of the spectrum of the exchange spin waves has been revealed in ferromagnet/ferromagnet multilayer films with a thickness of N(d ₁ + d ₂) by the spin-wave resonance method. This modification is due to the first bandgap at the wavenumber k _b = π/(d ₁ + d ₂) of a magnon crystal, which is formed by one-dimensional modulation of the magnetization. It has been shown that the transformation of the multilayer film with thermal annealing to the film of a single-phase alloy is accompanied by the disappearance of this modification of the spectrum.     

Spin-wave resonance in Co/Pd magnetic multilayers and NiFe/Cu/NiFe three-layered films

The spectrum of standing spin waves has been detected by the ferromagnetic resonance method in NiFe(740 Å)/Cu/NiFe(740 Å) three-layered film structure in the perpendicular configuration for the copper thickness d _Cu ≤ 30 Å. At thicknesses d _Cu > 30 Å, the resonance absorption curve is a superposition of two spinwave resonance spectra from individual ferromagnetic NiFe layers. For Co/Pd multilayer films, united spinwave responance spectra have also been observed at thicknesses of the paramagnetic palladium layer up to d _Pd < 30 Å. The partial exchange stiffness has been calculated for a spin wave propagating across the Pd layer (A _Pd = 0.1 × 10^?6 erg/cm). This value is always positive (up to the critical thickness of the palladium interlayer d _Pd < d _c) or equal to zero (d _Pd > d _c).     

Ferromagnetic and spin-wave resonance in Co/Pd/CoNi multilayer films

It has been found that the magnitude and sign of exchange interaction between Co(5 nm) and CoNi(5 nm) ferromagnetic layers through Pd depend on magnetization orientation of ferromagnetic layers. If magnetization is oriented in a layer plane, exchange interaction can be both ferromagnetic and antiferromagnetic. If magnetization orientation is orthogonal to a layer plane, the exchange constant is always positive at d_Pd<d _c and equals zero at d_Pd>d _c (d _c is the characteristic length).     

Spin-wave resonance spectra in bilayer magnetic films

The anti-Hermitian part of the high-frequency susceptibility tensor components in a bilayer film is calculated by solving the equation of motion for magnetization taking into account damping and using the exchange boundary conditions. The resultant expressions are used for determining the main parameters of the spin-wave resonance spectrum. Comparison of the calculated and experimental results demonstrates the correctness of the proposed method for calculating spectra.     

Magnetooptical properties of Fe/Pd multilayer films

Multilayer films of Fe(x)/Pd(30 Å) (6≤x≤30 Å) are investigated with the help of the transversal Kerr effect (TKE) with incident light in the energy range 1.3–3.6 eV. Oscillations of the TKE depending on the thickness of the iron layer are revealed. The off-diagonal element of the dielectric tensor ? ₂ ^′ is calculated using themeasured values of the TKE for two incidence angles of light and the optical constants of all samples. It is shown that the quantity ? ₂ ^′ ω² (where ω is the frequency of incident light), which is proportional to the interband density of states, also oscillates, and its oscillations are similar in character to oscillations of the Kerr effect. The observed oscillatory dependence of the TKE and of the interband density of states are related to the manifestation of quantum confinement effects.     

Spin-wave resonance and magnetic anisotropy in FePt thin films

Ferromagnetic Resonance (FMR) measurements at room temperature and X-band microwave frequency were performed on polycrystalline FePt thin films with face-centered cubic structure. With the external field perpendicular to the film plane, the absorption fields H_n of the odd and even spin-wave resonance modes n detected for the Fe_0.44Pt_0.56(45 nm)/Si(1 0 0) and Fe_0.51Pt_0.49(105 nm)/Pt(55 nm)/MgO(1 0 0) films, were found to obey the well-known H_n×n² ratio, giving for these films the exchange stiffness constant values of 3.9×10⁻⁸ and 4.4×10^–7 erg/cm, respectively. The study of the out-of-plane angular dependence of the absorption field of the uniform FMR mode allowed the measurement of the effective magnetic anisotropy constants of 5.3×10⁶ , 6.4×10⁶ , and 6.7×10⁶ erg/cm³, related, respectively, to the [1 1 1], [1 0 0], and [1 1 0] textures present in the films.     

Oscillations of the Faraday rotation in Co/Pd multilayer films

We have discovered oscillations of the Faraday rotation as a function of the thickness of Pd layers in Co/Pd multilayer films. A correlation is traced between the behavior of the Faraday rotation as a function of the thickness of the Pd layers and the magnitude of the saturation field determined from the field dependences of the Faraday rotation. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 735–738 (10 May 1996)     

Structural ordering and self-organization effects in multilayer Pd/Fe films

The structural features of the distribution of Pd and Fe atoms in multilayer films derived via Penning-discharge sputtering are studied. The preparation of films is a highly nonequilibrium process; at the same time, it is relatively simple in terms of possible structural implementations, which are shown during the self-organization of sputtered atoms through the formation of clusters with an individual ordered structure. It is important that the “dynamic chaos” that appears during sputtering is stabilized during crystallization, which makes it possible to study the resulting structures using nondestructive inspection methods with fairly wide possibilities. Therefore, it is of interest to study self-organization during the sputtering of multilayer films in order to reveal the mechanisms of cluster formation and to simulate them. It is also shown that the self-organization during sputtering and subsequent crystallization is accompanied not only by the ordering in the form of clusters, buts also by an ordered arrangement of these clusters.     

Magnetic resonance in multilayer Gd/Si/Co magnetic films

The magnetic properties of multilayer Gd/Si/Co magnetic films are experimentally studied by electron magnetic resonance and analyzed theoretically. The introduction of a semiconductor silicon interlayer is found to substantially affect the magnetic interlayer coupling and the magnetic dynamics of the system. The interlayer coupling is shown to be ferromagnetic for the (Gd/Si)_n films and to be antiferromagnetic for the (Gd/Si/Co/Si)_n films. The temperature dependences of the exchange parameters and the gyromagnetic ratios are determined. Possible mechanisms responsible for the formation of the interlayer coupling are discussed.     

Spin-wave resonance in magnetic films under conditions of the skin effect

The spin-wave resonance spectrum of a ferromagnetic film magnetized normally to its surface is investigated as a function of the finite depth of penetration of the high-frequency field into the film with due regard for damping in the spin system and different types of surface-spin pinning. The exact numerical solution of the equation of motion for magnetization is obtained by considering the finite thickness of the skin layer. For a substantially inhomogeneous distribution of the high-frequency field over the layer thickness, the change in the resonance shape at frequencies close to the ferromagnetic resonance frequency is observed in addition to the broadening of all the resonance peaks and the decrease in their amplitudes.     

Thickness dependent magnetization dynamics of perpendicular anisotropy Co/Pd multilayer films

We present the measurements of the picosecond magnetization dynamics of Co/Pd multilayer films. The dynamic magnetization properties of sputtered multilayer films were analyzed as a function of Co layer thicknesses and applied bias field. Both the eigenfrequencies of the magnetization precession in the multilayers and the associated Gilbert damping exhibit extreme sensitivity to the magnetic layer thickness on an atomic monolayer scale. The eigenfrequency increases more than threefold when the Co thickness decreases from 7.5 to 2.8 Å, mainly due to the changes in effective saturation magnetization and perpendicular anisotropy constant. A concomitant 2.6-fold increase in the damping of the oscillations is observed and attributed to stronger interface dissipation in thinner Co layers. In addition, we introduce a quasi-1D micromagnetic model in which the multilayer stack is described as a one-dimensional chain of macrospins that represent each Co layer. This model yields excellent agreement with the observed resonance frequencies without any free parameters, while being much simpler and faster than full 3D micromagnetic modeling.     

Spin-wave resonance spectra for two-layer films with strongly different uniform resonance fields in the layers

It is shown that, if the uniform resonance fields in the layers of a two-layer film differ considerably, the spin-wave resonance spectrum consists of two series of peaks corresponding to harmonic spin modes localized in the first and the second layer. This means that effective pinning of spins can be ensured by the layer in the state of a reactive (elastic) medium, as well as by the layer which is a dispersive medium for spin waves.     

Spin-wave dispersion in two-layer magnetic films

The change in spin-wave resonance spectra in multilayer magnetic films occurring under the gradual transformation of a spin-pinned layer from the reactive medium into a dispersive state or vice versa is studied. Spatial spin-wave dispersion associated with the spin-pinned layer is established to occur. This dispersion is most markedly pronounced in films with a mixed mechanism of spin pinning. The dispersion observed allows the so-called effect of “repulsion” of spin-wave modes to be accounted for.     

Spin-wave resonance spectra of films with a uniform gradient of anisotropy field

It has been shown that the number of high-intensity spin-wave modes in the spin-wave resonance spectrum of films with a uniform gradient of the effective anisotropy field depends on the thickness of the film and on the exchange stiffness. It has been established that there is a “critical” thickness of the film which depends on the exchange stiffness and the anisotropy field gradient. When the thickness of the film is less than the “critical” value, only one high-intensity mode is excited in the resonance absorption spectrum.     

Experimental study of the energy gap in the spin-wave spectrum in Co/Pd multilayer films

The energy gap appearing in the spin-wave spectrum as a result of Bragg scattering by the modulation period q=2π/(d ₁+d ₂) of a one-dimensional superlattice is observed by the method of spin-wave resonance in Co/Pd multilayer films. It is shown that this gap is asymmetric: The “positive” deviation is from two to three times greater than the “negative” deviation. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 12, 938–941 (25 June 1996)     

Angular dependence of the spin-wave resonance spectra in multilayer films

The angular dependence of the spin-wave resonance spectra is investigated in multilayer magnetic films in which the spin pinning mechanism changes from dynamical to dissipative. A fundamental difference is observed in the character of the angular dependences of the spectra for three-layer films as opposed to two-layer films. In particular, the number of peaks in the spectrum of three-layer films is observed to decrease and then increase twice as the angle between the magnetic field and the normal to the film is varied by π/2. Zh. Tekh. Fiz. 69, 97–101 (November 1999)     

Spin-wave resonance in a tangentially magnetized thin film

The imaginary part of the magnetic susceptibility determining the position, amplitude, and width of damped bulk and surface spin-wave eigenmodes in the spin system of a thin film magnetized in the film plane along the uniaxial bulk and surface anisotropy axis is analyzed numerically for various values of the degree of surface spin pinning. The presence of damping and the finiteness and asymmetry of the degree of surface spin pinning are shown to cause significant changes in the spin-wave resonance spectrum.     

Surface plasmon resonance biosensor modified with multilayer silver nanoparticles films

We alternately deposited negatively charged Ag-(3-mercaptopropionic acid) (Ag-MPA) sol and positively charged poly-(diallyldimethylammonium) (PDDA) on gold substrate modified with 4-aminothiophenol (4-ATP), through electrostatic layer-by-layer (LBL) self-assembly. We characterized the prepared three-dimensional Ag/PDDA multilayer films by surface plasmon resonance (SPR) and atomic force microscope (AFM). The thickness of each film in the multilayer films, the deposition effect of Ag nanoparticles, and the processing of DNA adsorption are characterized by SPR. AFM characterization shows that DNA/3(PDDA/Ag)/4-ATP composite is uniformly and firmly distributed on the surface of gold films. Compared with other sensors, gentamicin could be highly sensitively measured by DNA/3(PDDA/Ag)/4-ATP/Au sensor. There is a good linear relationship in the concentration range of 5 × 10⁻⁸ to 1 × 10⁻⁴ mol/L. The linear equation is found to be Δθ_SPR = 1.3521 × 10⁻⁵c + 0.08641 (the correlation coefficient is 0.9983) with detection limit of 1 × 10⁻⁹ mol/L. Since such LBL assembly film is simple to prepare, the work described here provides an effective method for studying small molecule drugs on SPR.     

Effect of diffusion and stresses on the magnetic properties of multilayer Fe/Pd and Fe/Ge films

Multilayer [Fe/Pd]₁₀ and [Fe/Ge]₁₀ films were studied using ferromagnetic resonance, magnetic-force and atomic-force microscopies, magneto-optical Kerr effect, and X-ray diffraction. It was shown that an increase in the interlayer thickness causes changes in magnetic parameters, such as the induced anisotropy, effective magnetization, coercive force, and the parameters of the fine magnetic structure. Reasons of the changes in the magnetic parameters were established.