Theory Of Spin-wave Resonance Research Articles

Spin-wave resonance in gradient ferromagnets with concave and convex variations of magnetic parameters

The theory of spin-wave resonance in gradient ferromagnetic films with magnetic parameters varying in space described by both concave and convex quadratic functions is developed. Gradient structures such as a potential well, a potential barrier, and a monotonic change in potential between the film surfaces for both quadratic functions are considered. The waveforms of oscillations mn(z), the laws of the dependence of discrete frequencies ωn, and relative susceptibilities χn/χ10 of spin-wave resonances on the resonance number n are studied. It is shown that the law ωn∝n for n<nc, where nc is the resonance level near the upper edge of the gradient inhomogeneity, which is well known for a parabolic potential well, is also valid for the potential barrier and for the monotonic change in potential, if these structures are formed by a concave quadratic function. It is shown that the law ωn∝(n−1/2)1/2, which we numerically derived and approximated by the analytical formula, is valid for all three structures formed by a convex quadratic function. It is shown that the magnetic susceptibility χn of spin-wave resonances for n<nc is much greater than the susceptibility of resonances in a uniform film. An experimental study of both laws ωn(n) and χn(n) would allow one to determine the type of quadratic function that formed the gradient structure and the form of this structure. The possibility of creating gradient films with different laws ωn(n) and the high magnitude of the high-frequency magnetic susceptibility χn(n) at n<nc make these metamaterials promising for practical applications.

Observation of two-critical-angle phenomenon in spin wave resonances in diluted ferromagnetic semiconductor GaMnAs thin films

We have studied surface anisotropy energy and surface pinning parameters of ferromagnetic semiconductor GaMnAs film by analyzing spin wave resonance (SWR) measurements carried out on this material. The SWR spectra were observed in various polar and azimuthal angular orientations of external static magnetic field with respect to crystal axes of an annealed GaMnAs film with a Mn concentration of 8.0 at.%). The observed SWR spectra were interpreted in terms of a recently developed spherical surface pinning (SSP) theory. As predicted by the SSP theory, our data clearly show the existence of two critical angles in specific resonance configurations. The experimental confirmation of this key prediction of the SSP model brings new insights into the behavior of magnetic surface anisotropy of GaMnAs films. In particular, the agreement of our experimental results with SWR theory shows that, by including higher-order terms with cubic symmetry in the description of the surface free energy, our analysis will improve our understandings of the magnetic surface anisotropy of GaMnAs films.

Surface anisotropy energy in terms of magnetocrystalline anisotropy fields in ferromagnetic semiconductor (Ga,Mn)As thin films

Surface anisotropy energy density is a key quantity in the description of the dynamics of surface spins in ferromagnetic thin films and is known to result in a ferromagnetic resonance fine structure of a thin film: A multipeak spectrum is observed in an effect known as spin-wave resonance (SWR). The so-called surface pinning parameter, directly correlated with the surface anisotropy energy, plays a fundamental role in determining the character of an SWR spectrum in the theory of SWR based on the surface inhomogeneity model. Here we extend the theory of SWR by introducing a new formula representing the surface pinning parameter as a series of contributions from different anisotropies existing in (Ga,Mn)As thin films. We show how to determine the coefficients in this series by comparing the SWR theory with data obtained in a resonance experiment. The proposed procedure allows one to determine the proportion with which each type of the anisotropy contributes to the total surface anisotropy of (Ga,Mn)As, and, consequently, to assess to what extent the proportions on the surface differ from those in the bulk. The presented considerations can be used for the study of any other thin-film system, since we provide also a general rule that allows one to express the surface pinning parameter of a thin film, as well as its surface anisotropy energy, by the free energy of the considered thin-film system. This enables the interpretation of experimental SWR spectra in terms of the free-energy density of the thin film.

Spin-wave resonance and magnetization studies in La0.7Mn1.3O3 films

Spin-wave resonance (SWR) in high quality epitaxial La 0.7 Mn 1.3 O 3 films prepared by dc-magnetron sputtering was studied at a frequency of 9.25 GHz. SQUID magnetometry was used to study the film magnetization. A well-resolved structure of the SWR spectrum consists of surface and bulk spin waves modes. The experimentally found SWR spectra are in good agreement with the theory of SWR based on the surface-inhomogeneity model. Using the SWR and magnetization data, the spin-wave stiffness constant and the values of the bulk anisotropies were deduced.

Thickness and temperature dependence of magnetic anisotropies of Ni 77Mn 23 films

Magnetic properties of polycrystalline reentrant Ni 77Mn 23 films of various thickness ( 50, 100, 300, 600, 1000 and 3700 Å) were studied by both spin wave resonance (SWR) and DC magnetization techniques as a function of temperature. All films show spin-glass properties at the temperature range below freezing temperature T f (≅120 K). For temperatures well-above T f, most of the films exhibit multi-peak ESR spectra at both X-and Q-band when the external field is oriented within a small interval of a solid angle around the film normal. The number of peaks increases with film thickness, indicating long spin wave excitation across the film thickness. The angular dependent SWR spectra were successfully analyzed by usual classical SWR theory. Hence, the SWR parameters were deduced for magnetic energy density including Zeeman, effective magneto-crystalline and unidirectional bulk and surface anisotropies, oblique anisotropy, spin-wave energy (exchange energy) and magnetic damping terms. The effective exchange stiffness parameter ( D) remains practically the same for all films above T f, while its value surprisingly increased below T f, showing a strong correlation with spin-glass properties. The films also show easy-axis (perpendicular to the film plane) bulk and easy-plane surface anisotropy energies. The bulk anisotropy was found to strongly increase with decreasing temperature and film thickness, while linearly a temperature dependent surface anisotropy showed a very weak thickness dependence. This easy-plane surface anisotropy on both substrate and free surfaces has been attributed to an intrinsic property for NiMn films rather than accidental surface condition that could be varied from film to film due to variable sample preparation conditions. Furthermore, the spin disorder becomes more significant for thicker films.

Theory of surface states in spin wave resonance

Following a concise review of present achievements in the study of magnetic surface states by spin wave resonance, a discussion of surface state theory and experimentally observed effects is given. The theoretical treatment, starting from the general model assumptions made when dealing with thin magnetic films, concentrates specifically on the Surface Inhomogeneity Model, for which a Hamiltonian is established and diagonalized, leading to the elementary magnetic excitation i.e. spin waves of the system. The appropriate spin wave resonance theory is developed in detail, and the resonance effects are expounded on the basis of a Pinning Diagram, especially constructed for this purpose. Particular attention is given to the existence conditions for surface states, the experimental identification of their respective resonance lines, as well as the use of these lines when determining the surface conditions of the thin film and measuring its magnetic surface anisotropy. The analysis of the surface state properties is based on the exact solution of the eigenvalue problem of a finite linear chain with arbitrary (asymmetric) boundary conditions.

Tensorial Surface Anisotropy in the Theory of Spin‐Wave Resonance

physica status solidi (b)Volume 63, Issue 2 p. K115-K119 Short Note Tensorial Surface Anisotropy in the Theory of Spin-Wave Resonance† H. Puszkarski, H. Puszkarski Institute of Physics, A. Mickiewicz University, PoznańSearch for more papers by this author H. Puszkarski, H. Puszkarski Institute of Physics, A. Mickiewicz University, PoznańSearch for more papers by this author First published: 1 June 1974 https://doi.org/10.1002/pssb.2220630245Citations: 6 † This project was assisted by the U.S. National Science Foundation. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume63, Issue21 June 1974Pages K115-K119 RelatedInformation

Theoretically predictable effects and new interpretations in spin wave resonance of thin films with asymmetric boundary conditions

AbstractThe eigenvalue problem of the finite linear chain with arbitrary asymmetric boundary conditions is solved strictly. The results are used in quantum theory of spin wave resonance (SWR) in thin asymmetric ferromagnetic films. A theory providing some new interpretations of experimentally known effects in SWR and predicting new as yet unobserved effects is proposed. The results are visualized in an especial surface pinning diagram which should prove highly useful for the comparison of experimental data with the theory.

A note on the theory of spin wave resonance in spiral structures

The appearance of two resonant modes of spin waves with different non-zero wave vectors is theoretically predicted for a magnetic arrangement of the type of an antiferromagnetic spiral combined with weak antiferromagnetism in the direction of the spiral axis. A study is made of the question of the Hamiltonian suitable for possible applications of the chosen magnetic arrangement, and the possibility of energetic stability of the considered magnetic structure for two concrete realistic forms of the Hamiltonian is pointed out.

Standing spin waves in ferromagnetic thin films

A theory of spin wave resonance in ferromagnetic thin films is discussed in a manner that permits a computation of the real and imaginary parts of the circularly polarized RF fields as well as the power absorption spectrum. The case of the dc field intensity applied normal to the surface of the film is considered, and the saturation magnetization is taken as constant throughout the body of the film. Variations in dc fields near the surfaces are treated in the boundary conditions for the RF magnetization by considering the unsymmetrical nature of the exchange interaction at the surfaces. The boundary conditions are characterized by a constant for each surface that controls the degree of surface pinning in the RF magnetization. Damping is included in the formulation by means of a phenomenological constant in the spin wave equation and by simulaneous solution of this equation with Maxwell's equations for a conductor. The results of a computer program are presented showing the roles of the various parameters in determining the power absorption spectrum and RF fields. A comparison with experimental spectra is made, and an anomalous resonance at field intensities higher than that for the principal resonance is predicted.

Nonuniform magnetization models in the theory of spin-wave resonance in a thin ferromagnetic film

Nonuniform magnetization models in the theory of spin-wave resonance in a thin ferromagnetic film

Theory of Spin-Wave Resonance in Thin Films

A new theory of spin-wave resonance, based upon the assumption that the saturation magnetization varies linearly across the thickness of the film, is described. The characteristic equation for the normal modes has been solved both for free and for strongly pinned surface spins. According to this theory the lower-order modes are approximately equally spaced, their separation in magnetic field being given by δH≃1.5 (H0′)⅔D⅓, where H0′ is the field gradient and D=2A/M0 a phenomenological exchange constant (A = Landau-Lifshitz constant, M0 = saturation magnetization). The theory agrees remarkably well with the experimental data of Nisenoff and Terhune on Permalloy films.