Using local ferromagnetic resonance spectroscopy, we have studied the magnetic properties near edges of thin tangentially magnetized permalloy films, in which a well-defined uniaxial magnetic ...anisotropy was induced perpendicular to one of the edges. In the experiment, two samples with thicknesses of 90 and 300 nm and with slightly different compositions were examined. To explain the magnetization dynamics near edges, we propose a simple yet effective model of a film in the form of a rectangular prism, which yields the modified Kittel formula for the resonance frequency. In this formula, the locally averaged distance-dependent demagnetizing field that emerges near the edges is included as an additional uniaxial anisotropy term. The measurements reveal that at a certain distance from the edge, the resulting (apparent) anisotropy, determined from the angular dependencies of the resonance field, almost vanishes. Moreover, its easy axis reorients to become parallel to the edge. The model predictions agree well with these results, proving that the main resonance mode behavior near the film edges can be accurately described by introducing additional effective uniaxial anisotropy, provided the measuring area is relatively large. However, for the thick (300 nm) sample, additional precession modes are also observed. These modes distort the angular dependence of the main mode, thus demonstrating the limitations of the model.
•Grain size is a key parameter determining magnetic properties of nanocrystalline films.•Stochastic magnetic structure—magnetization ripple—is formed in such films.•If grain exceeds critical size, ...FMR line broadening occurs at certain frequencies.•Effects are caused by two-magnon scattering of spin waves on magnetization ripple.
The size of crystallites is one of the most important factors that determine the key characteristics of nanocrystalline thin magnetic films that make them very promising media for various applications. In this paper, using micromagnetic simulation, we study in detail the influence of the grain size on the magnetic microstructure of the films and its relation with high-frequency dynamics of magnetization. When the grain size exceeds some critical value Dcr, a sharp broadening and shift of the ferromagnetic resonance line are observed at certain frequencies of the alternating magnetic field. Using a two-magnon scattering model, it is shown that these effects are caused by the scattering of spin waves on the inhomogeneous stochastic magnetic structure—magnetization ripple. An expression for the determination of the critical size Dcr is obtained. The micromagnetic simulation results agree with the main conclusions of the static and dynamic theories of magnetization ripple and also confirmed by experimental data reported by other authors.
•Permalloy films with various crystallite sizes were made by magnetron sputtering.•New effect of a sharp broadening and shift of ferromagnetic resonance line is found.•The revealed effect is of the ...threshold nature.•The effect occurs when the crystallite size is greater than the critical value.•The effect is caused by two-magnon scattering of spin waves on magnetic structure.
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With the rapid development of telecommunication technologies and highly integrated electronic devices, researchers show great interest in nanocrystalline soft magnetic thin films with unique characteristics for microwave applications. An important direction of the current research in this field is the study of high-frequency magnetization dynamics that directly depends on the damping processes in a magnetic medium. This paper reports on the effect of sharp broadening and shift of the ferromagnetic resonance (FMR) line revealed experimentally in a 40-nm-thick nanocrystalline permalloy (Fe20Ni80) thin film at a frequency of about 5 GHz. The effect arises only in films with crystallite size exceeding some critical value Dcr. The micromagnetic simulation demonstrates that exchange and dipolar interactions between randomly oriented crystallites form in the film a quasiperiodic magnetic structure with a characteristic wavelength in the range from 36 nm to 3.3 µm. An analysis of the two-magnon scattering model and simulation results shows that the formed magnetic structure provides the energy transfer from uniform magnetization oscillations (uniform FMR) to spin waves, which results in an additional energy dissipation channel and, consequently, sharp FMR line broadening. A theoretical estimate of the critical crystallite size Dcr based on this model yields a value of ~14.3 nm for 40-nm-thick Fe20Ni80 films.
An athlete's diet is influenced by external and internal factors that can reduce or exacerbate exercise-induced food intolerance/allergy symptoms. This review highlights many factors that influence ...food choices. However, it is important to remember that these food choices are dynamic, and their effectiveness varies with the time, location, and environmental factors in which the athlete chooses the food. Therefore, before training and competition, athletes should follow the recommendations of physicians and nutritionists. It is important to study and understand the nutritional strategies and trends that athletes use before and during training or competitions. This will identify future clinical trials that can be conducted to identify specific foods that athletes can consume to minimize negative symptoms associated with their consumption and optimize training outcomes.
Two numerical micromagnetic methods most suitable for calculation of the high frequency magnetic susceptibility of nanocrystalline thin films were considered in detail. The methods are based on the ...Landau–Lifshitz equation, linearized around the equilibrium state leading to an eigenvalue problem or solved using an undetermined coefficients technique. An analysis and estimation of an efficiency of the methods were carried out. Several conclusions about their advantages and shortcomings, as well as specifics of their practical application were drawn.
•Modelling of magnetization dynamics of nanocrystalline thin films is a challenging task.•We analyze two numerical methods for film's high frequency susceptibility calculation.•An eigenvalue-based method is more informative, but is computationally costly.•An undetermined coefficients method is more suitable to model nanocrystalline films.
Thin magnetic films with periodic surface topography are of special interest for microwave applications as their static and dynamic magnetic characteristics can be readily adjusted. In this paper, we ...explore the capabilities of a simple method for producing large-area periodically patterned films by creating regularly spaced grooves on a substrate using a diamond cutter. For 110-nm-thick films, it was found that the substrate-topography-induced magnetic anisotropy was inversely proportional to the pattern period, which in experimental samples varied from 5 to 20 μm. Based on the Netzelmann theory, analytical expressions for demagnetization tensor components were obtained, which accord well with the experimental data. The measurements of the natural ferromagnetic resonance spectra demonstrated that the increase of the topography-induced magnetic anisotropy with the decrease of the pattern period led to the increase of the resonance frequency from 0.65 to 1.86 GHz, and to a decrease of the linewidth and effective damping parameter.
•A simple technique to fabricate parallel microgrooves on substrates was used.•Grooved substrates transform the properties of permalloy films deposited on them.•The grooves period controls magnetic anisotropy and ferromagnetic resonance frequency.•The Netzelmann approach was used to calculate magnetic anisotropy of grooved films.•The grooves also control the magnetization damping parameter.
Magnetic characteristics and their spatial distribution of magnetron sputtered nanocrystalline NiFe thin films of various compositions were investigated by ferromagnetic resonance (FMR) and ...magneto-optical Kerr effect microscopy. A sharp increase in the FMR linewidth and a strong deviation of the uniaxial magnetic anisotropy field were observed near the film edges. It was shown that the observed magnetic anisotropy behavior can be explained by assuming that besides the field-induced uniaxial magnetic anisotropy an additional source of the uniaxial anisotropy near the film edges exists, with the easy axis parallel to the edges. The possible origins of this additional contribution were discussed.
Distribution of the magnetic anisotropy in thin film prepared by thermal vacuum oblique deposition of permalloy with small off-normal angle of incident in the presence of an external magnetic field ...has been studied by ferromagnetic resonance technique. On local area of the sample, a mutual compensation of near orthogonal in-plane uniaxial magnetic anisotropies induced by oblique deposition and by applied magnetic field has been found. Moreover, in addition to the uniaxial (twofold) magnetic anisotropy, fourfold and sixfold magnetic anisotropies have been observed in the sample. To explain the obtained high-order anisotropies, we assumed that the sample has exchange coupled adjacent regions or phases with different parameters of magnetic anisotropy. The results of the micromagnetic analysis of a two-layer model of the sample confirm the hypothesis.
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