Theory of ferromagnetic resonance line shape in insulators

The paper discusses the absorption of the energy of a high-frequency field by a magnetic sample from the point of view of the interaction of spin waves with photons and spin waves amongst themselves. A general expression for the form of the absorption curve is derived, using the method known from the quantum theory of radiation and assuming very weak fields.

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The author thanks S. Krupika, Candidate of Sciences, for the exceptional interest taken in this work, for advice and a number of helpful and critical remarks.     

The microwave resonance line shape in ferromagnetic cubic FeGe

The ferromagnetic resonance as well as the antiresonance in cubic FeGe have been studied in the temperature range 77–300 K using the frequencies 9·5 and 35 GHz. The observed line broadening was found to be due to the shape of the samples. Experimentally determined values are given for saturation magnetizations, g-factors and demagnetization factors. The latter differ considerably from those calculated in the ellipsoidal approximation. The g-factor increases from 2·07 at 35 GHz to 2·18 at 9·5 GHz. The line shape of the magnetic resonances has been calculated for an external magnetic field parallel as well as perpendicular to the plane of a disc-shaped sample. The calculations are outlined in the paper and the results are presented in the form of the derivatives of the calculated spectra. The latter are found to be in excellent agreement with experimental results. Exchange and spin pinning turned out to have negligible influence on the lines. The theoretical results have been obtained from the perturbation theory of Lax and Button which was modified by augmenting the dynamic susceptibility with a constant in order to account for the behavior of the cavity fields at the walls.     

Analysis of magnetic resonance line shape under slow molecular motions

A new approach is considered to the analysis of the magnetic resonance line shape under slow molecular motions. The essence of the approach consists in calculating the coefficientsa _n in the Taylor expansion G(t). A straightforward procedure has been developed for calculating the coefficientsa _n for molecular motions described by random Markov processes.Translated from Izvestiya Vysshikh Uchebnyh Zavedenii, Fizika, No. 7, pp. 48–52, July, 1982.     

Nuclear magnetic resonance in ferromagnetic terbium

The temperature dependence of the magnetic dipole and electric quadrupole hyperfine fields has been measured by NMR in ferromagnetic terbium metal. The results are in excellent agreement with a general theoretical relation connecting moments of the magnetization. This relation allows us to separate ionic and crystalline contributions to the nuclear electric field gradient.     

Width of the ferromagnetic resonance line in an anisotropic magnet in misoriented resonance and scanning magnetic fields

The dependence of the width ΔH_β of the ferromagnetic resonance (FMR) line in anisotropic magnets on the angle of misorientation β between the static (resonance) and scanning magnetic fields was investigated both experimentally and theoretically. The change in the linewidth is due to the dependence of the equilibrium orientation of the magnetization vector on the direction of the magnetic field upon the passage through the resonance. Using iron garnet films as an example, it was shown that under such a misorientation (a nonzero angle β) the linewidth is smallest. It was also shown that a two-dimensional representation of FMR spectra, in contrast to one-dimensional angular dependences of the resonance parameters, contains full information on the spectral characteristics of the film, including noncollinear field configurations.     

Influence of an electric field on the ferromagnetic resonance in a plane-layered magnetic system

The influence of an electric field on the ferromagnetic resonance (FMR) in a multilayer magnetic system consisting of two magnetic layers separated by a thin nonmagnetic interlayer has been investigated. It has been shown that, upon the excitation of magnetization oscillations by a microwave magnetic field, the eigenfrequencies of the ferromagnetic resonance depend on the stationary electric field applied in the plane of the layers. It has also been demonstrated that, in this system, high-frequency magnetization oscillations can be excited by an electric microwave field. The results of the investigation of the polarization properties of the excitation mechanism indicate that this effect can be observed experimentally.     

Magnetic resonance line shape

The long-time asymptote of the magnetization correlation function and its distribution are investigated with slow motion of the spin and molecular subsystem taken into account the most. The influence of molecular drift in the field of the thermal hydrodynamic fluctuations on the magnetic resonance line shape is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 118–121, May, 1976.     

The experimental investigation of the spin packet line shape in an inhomogeneous magnetic resonance line

It is shown that the saturation transient of an inhomogeneous spin system is strongly affected not only by the width but also by the shape of the spin packets. In two cases of main interest, Lorentzian and Gaussian packets, we report approximate analytical expressions of χ(t) during the saturation transient, with which the experimental results may be compared. By this method we give experimental evidence that the packet profile in dilute ruby samples has a Gaussian shape.     

铁磁共振法测磁各向异性

采用铁磁共振方法,研究了铁磁/反铁磁双层膜系统中,因交换耦合以及磁晶各向异性而产生的有效各向异性场.结果表明:被测系统有无交换偏置场以及其正负号性质等均能在共振谱中得到辨析.结果还显示:沿着不同结晶方向施加外磁场,共振场的行为与磁晶各向异性以及铁磁/反铁磁交换耦合作用而诱发的单向各向异性等密切相关.将共振频率的变化看成外磁场(包括其方向和大小)的函数,研究得到了单向各向异性,立方各向异性等对共振频率的影响,并同实验结果做了很好的比较. 关键词： 铁磁/反铁磁双层膜 交换耦合 铁磁共振 单向各向异性     

Defect mode suppression in a photonic crystal with a magnetic defect in the ferromagnetic resonance region

The specific features of the transmission and reflection spectra of a one-dimensional photonic crystal structure with a magnetically active layer placed between dielectric Bragg mirrors have been investigated. If the magnetic resonance frequency coincides with the frequency of the defect mode in one of the photonic bands, the defect mode in the photonic crystal can be completely suppressed, which makes it possible to effectively control the spectrum of such a structure by an external magnetic field.     

Local ferromagnetic resonance imaging with magnetic resonance force microscopy

We report nanoscale scanned probe ferromagnetic resonance force microscopy (FMRFM) imaging of individual ferromagnetic microstructures. This reveals the mechanism for high spatial resolution in FMRFM imaging: the strongly inhomogeneous local magnetic field of the cantilever mounted micromagnetic probe magnet used in FMRFM enables selective, local excitation of ferromagnetic resonance (FMR). This approach, demonstrated here in individual permalloy disks, is straightforwardly extended to excitation of localized FMR modes, and hence imaging in extended films.     

Anomalous shape of cyclotron resonance line in n-GaP in high magnetic fields

Cyclotron resonance in n-GaP has been observed at 119 μm in pulsed magnetic fields up to 410 kG. From the experiments with the magnetic field parallel to the 〈100〉, 〈110〉 and 〈111〉 axes, it is concluded that the transverse effective mass for electron is and that the anisotropy factor of the conduction band is K = 7.9^+3.2_?2.0. An anomalous shape of the absorption curve was found in the magnetic field directions parallel to the crystal axes 〈110〉 and 〈111〉.     

Equation of the ferromagnetic resonance line in polycrystalline ferrites

Ferromagnetic resonance in polycrystalline ferrites is considered in the framework of the independent-grain model. It is shown that the ferromagnetic resonance absorption line can be obtained analytically from its moments. When a limited number of moments of the line are known explicitly, the method of Pearson curves is used to obtain the equation of the line. The obtained expression is analyzed and the resonance field and absorption line width deduced from the equation are compared with results obtained earlier.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 19–23, March, 1981.