Surface Spin-wave Modes Research Articles

A dipole-exchange theory for Brillouin light scattering from ferromagnetic thin films

A dipole-exchange theory is presented for Brillouin light scattering from the surface and bulk spin-wave modes propagating in perpendicularly magnetized films with general asymmetric pinning at the surfaces. The approach is based on a spin-wave theory with mixed exchange boundary conditions and a Green’s-function (linear-response) formalism for light scattering from magnetic films. The influence of dipole-dipole hybridization of the spin-wave dispersion branches on the calculated light-scattering intensities is taken into account, and the dependence of the Brillouin spectra on the pinning conditions investigated. Applications of the theory to Fe thin films are discussed.

Investigations of bulk and surface spin wave modes in FeNi multilayers by spin wave resonance

The SWR spectra of an FeNi multilayer have been studied experimentally and theoretically. Non-propagating surface spin wave modes as well as standing volume modes could be observed. Values of the surface anisotropy, the spin wave stiffness constant and the effective magnetisation have been deduced from the spectra. The results obtained by SWR and torque measurements are discussed.

Theory for Brillouin light scattering from dipole-exchange surface spin waves in ferromagnetic films

A theory is presented for Brillouin light scattering from spin-wave excitations in ferromagnetic films. The approach is based on a tensorial Green-function theory of the dipole-exchange spin wave spectrum in magnetic films. Mixed exchange boundary conditions are used, and the particular case of antisymmetric pinning in perpendicularly magnetized ferromagnetic films is discussed in detail. Explicit analytical expressions for the light-scattering cross sections are obtained in this case of scattering from both surface and bulk spin-wave modes. Applications of the theory to films of Fe and EuO are discussed. >

Spin wave resonance in FeAlN films

Results are presented on the 33-GHz ferromagnetic resonance and spin wave resonance spectra of single and multilayer NiFe/FeAlN films deposited by RF diode sputtering. The following films were prepared: FeAlN/glass, NiFe/glass, NiFe/FeAlN/glass and NiFe/FeAlN/NiFe/glass. For all the FeAlN films a spectrum of volume spin waves is observed. The exchange constant A calculated from the spin wave resonance spectrum is between 1.6 and 1.8*10/sup -6/ erg cm/sup -1/. The effective anisotropy field 4 pi M/sub s/ and g-values are -17.7 kOe, 18.1 kG, 2.19 and -9.1 kOe, 9.4 kG, 2.14 for the FeAlN and the NiFe, respectively. In the bilayer and the trilayer films, an extra resonance is observed which lies at a field value in between the NiFe and FeAlN resonances for the in-plane applied field. This resonance is attributed to a surface spin wave mode. >

Temperature dependence of magnetization in nickel thin films

The spin-wave density of states for Ni thin films is calculated within the framework of the multiband model. Parameters of the model are chosen in such a way that one-electron ground state results consistent with ab initio theories are obtained. The calculated surface density of states is considerably enhanced as compared to the density of states in the central layer. The enhancement is a result of the presence of the acoustic surface spin-wave modes. The temperature dependence of the magnetization is also investigated. It is obtained that the surface magnetization decreases faster than the central layer magnetization. A range of the temperatures in which the magnetization decreases according to a T 3 2 law is found.

Surface phase transitions and spin-wave modes in semi-infinite magnetic superlattices with antiferromagnetic interfacial coupling.

We analyze the bulk and surface spin-wave modes of a semi-infinite Fe/Gd superlattice. If an externally applied magnetic field is increased from zero, one surface mode is driven soft, indicating a surface phase transition which occurs at a field value about 5 times lower than that necessary to cause a bulk phase transition. The phase transition is shown to nucleate at the surface and has a large penetration depth (on the order of a few hundred angstroms) even for fields just slightly above the value needed to induce the transition.

Photoinduced Effect on Magnetic Properties of Ion-Implanted YIG Thin Films--Resonance Field Dependence on Annealing Temperature in Hydrogen Atmosphere

The photoinduced effect studied here is the decrease ΔH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> in the ferromagnetic resonance field of surface spin wave modes in an ion-implanted layer of YIG film during optical illumination. The H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> or He <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> implanted films were annealed in a hydrogen gas atmosphere. The results on annealing show various ΔH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> behavior caused by the implanted and diffused hydrogen, and the formation of a large anisotropy in the surface layer of the He <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -implanted films. Proposed models for changes in the chemical reaction between hydrogen and ferrous ions, and the origin of the large anisotropy, are discussed.

イオン打込みＹＩＧ薄膜の光磁気効果 水素中アニーリング依存性

The photoinduced effect of this study is presented as the decrease ΔHp of ferromagnetic resonance field of surface spin wave modes in an ion-implanted layer of YIG films during light irradiation. The H2+ or He+-implanted films are annealed in a hydrogen atmosphere. The results with annealing show various behaviors of ΔHp caused by implanted and diffused hydrogen, and the formation of large anisotropy in the surface layer of He+ -implanted films. Proposed models on the changes of chemical reaction between hydrogen and ferrous ion and the origin of the large anisotropy are discussed.

Relaxation of photoinduced effect on surface spin-wave modes in H+2 -implanted YIG thin films (abstract)

Previously Tsuchiya and Uematsu reported their discovery of a photoinduced effect in which the decrease ΔHp of ferromagnetic resonance field of surface spin-wave modes in the H+2 -implanted layer of YIG thin films is observed during light irradiation at 77 K, and etching depth dependence of ΔHp is measured. The decrease ΔHp in as-implanted films is attributed mainly to generation of Fe2+ ions with hydrogen presence. The main hydrogen distribution has been introduced from the study.1 Here the authors describe ΔHp relaxation as the irradiation is turned on and off in the cases of as-implanted films and films covered with a sputtered SiO2 layer, before and after annealing. (111)-oriented YIG films are used. The energy of H+2 implantation is 30 keV and the dose is 1×1016 ions per cm2. The FMR frequencies are 9.2–9.4 GHz. First, an as-implanted film is irradiated for 10 min without applying a magnetic field and then after removing the irradiation ΔHp is able to be observed (class II). Next, ΔHp is measured to increase during irradiation with a field (class I), and then after removing ΔHp decreases to a class II level. Class I and II are explained from ‘‘one-center model’’ and ‘‘two-center model’’ of photoinduced magnetic anisotropy effect,2 respectively. Relaxation of ΔHp mentioned above, as well as that of ΔHp about films covered with SiO2 are measured and their particular properties are discussed.

Conditional replaceability of magnetic surface anisotropies by effective volume anisotropies in the ferromagnetic resonance of ultrathin films

Specific conditions are proposed for the replaceability of magnetic surface anisotropies by effective volume anisotropies and for the concomitant replaceability of the actual ferromagnetic resonance (FMR) surface mode or spin wave mode by a uniform mode. These conditions are then applied to the parallel and perpendicular FMR configurations in monocrystalline and amorphous ferromagnetic films. The significance and limitations of the results are discussed.

Strong influence of magnetic surface anisotropies on the Damon-Eshbach mode frequency of ultrathin Fe(110) layers (abstract)

Epitaxially grown Fe(110) layers on W(110) with thicknesses between 8 and 150 Å have been investigated in situ by Brillouin scattering. A strong increase of the frequency of the Damon-Eshbach (surface spin wave) mode by a factor of up to 3 has been observed with decreasing layer thickness below 60 Å. The frequency increase is accompanied by a strong line width broadening. In good agreement with earlier observations,1–3 the change over of the easy axis of the saturation magnetization from [001] to [1-10] could directly be observed at a critical thickness dc=95±5 Å with an applied residual magnetic field of 30 G. The anomalous behavior of the Damon-Eshbach mode is quantitatively described by a model fit, which takes explicitly into account magnetic surface anisotropies. The magnetic in-plane surface anisotropy constant Ks,p=2.4×10−2 erg cm2 has been calculated from the literature value of the bulk anisotropy constant K1, the residual applied magnetic field and the critical thickness dc, using the homogeneous magnetization approximation.2 The fitted value of the magnetic out-of-plane anisotropy constant Ks=2.8±0.7 erg/cm2 is smaller than the value obtained for the case of Fe(110) on GaAs(110).1 While for Fe thicknesses larger than 30 Å the film quality is not very crucial for the spin-wave spectra, 10-Å-thick films show a strong increase of the Damon-Eshbach mode frequency with increasing density of steps on the surface. Since these steps are aligned parallel to the [001] direction as observed by LEED, we attribute the frequency increase to additional uniaxial surface anisotropies induced by the steps. On the other hand, the formation of islands leads to a frequency decrease due to reduced anisotropies.

Spin-wave resonance in CoCr magnetic thin films

Spin-wave resonance spectra were observed at 9.8 and 35.2 GHz in CoCr thin magnetic films on both silicon and glass substrates. The perpendicular spectra of samples on the glass substrates had both even and odd numbered modes, while the perpendicular spectra of samples on silicon substrates had only odd numbered modes. The films had HKeff =−5.9 to −7.4 kOe and geff =2.12–2.38 for the most intense mode in the perpendicular spectra. The lower values of HKeff were observed for the films on the silicon substrates. Evidence of a surface spin-wave mode was seen in some of the spectra as a less intense mode observed at a higher applied field than the most intense mode in the perpendicular spectra. The resonance fields of the modes with mode number n&amp;gt;4 followed the n2 dispersion relation from which the exchange constant A has been estimated as A=1.0×10−6 erg/cm. The films had other resonances besides the spin-wave modes and the results of VSM studies showed evidence of a transition layer effect in the in-plane hysteresis loop. The results of x-ray diffraction studies show the films have predominate 002 growth axis on both substrates. The SEM cross section did not show any evidence of columnar structure on either of the substrates.

Vortices in 3He–A in Restricted Geometries

We have studied vortices in 3He–A between a stack of plates with about 20 µm spacing and within an array of long cylinders of 0.5 mm diameter. Taking advantage of localised surface spin-wave modes, trapped by the \\hatℓ texture near the walls, we have determined the critical velocity for vortex formation as well as the pinning velocity for vortices in the plate geometry. In 0.5-mm cylinders vortices are similar to those in the bulk liquid but a broad hysteresis in the number of vortices (1-4/tube) is observed when the cryostat is accelerated or decelerated.

Temperature dependence of FMR surface spin-wave mode of amorphous Fe 40Ni 40B 20 alloys

The temperature dependence (3 to 300 K) of the FMR surface spin-wave mode on annealed ribbons of the Fe 40Ni 40B 20 alloy was measured at 48 GHz. Using the macroscopic FMR theory the values of the surface anisotropy constant were determined as 1.15 erg/cm 2 at 3 K decreasing to 0.6 erg/cm 2 at 293 K; the exchange-stiffness constant at 0K amounts to 169 meVå 2.

Observation of FMR Surface Spin Wave Mode in Bulk Amorphous Ferromagnets

AbstractA secondary mode is observed (at RT) in the FMR spectra of the bulk amorphous alloy Fe40Ni40B20 subjected to an anneal at 250°C. This mode is interpreted as the surface spin wave mode because the observed magnetic resonance field dependences on the microwave frequency and on the direction of the external field towards the sample surface agree with the conclusions of the macroscopic FMR surface‐mode theory.

Long-Wavelength Surface Spin Waves on Antiferromagnets

The first discussion of a long-wavelength, magnetostatic, surface spin-wave mode on uniaxial antiferromagnets is presented. In the absence of an applied field, the frequency of the surface wave depends on the angle between the direction of propagation and the easy axis. With a magnetic field applied parallel to the surface, and along the easy axis, the surface mode does not propagate in all directions, but is limited to a restricted set of angles.

Effects of Surface Spin Waves and Surface Anisotropy in Magnetic Thin Films at Finite Temperatures

AbstractThe validity of the Green function theory developed by Haubenreisser et al. for ferromagnetic thin films (TF) is investigated. Their method, although to rough for the calculation of magnetization spatial distribution, is found useful for the calculation of critical temperature. By using their method, the effect of surface spin wave modes on the critical temperature is analyzed of both ferro‐ and antiferromagnetic TF. The film thickness dependence and the surface anisotropy dependence of the critical temperature are presented. The condition of the appearance of the so‐called “hard surface” and “pinned spin wave” is discussed. The effect of temperature in ferro‐ and antiferromagnetic resonance is also studied.

Spin wave resonance in single-crystal nickel films

The room-temperature observation of extensive spin wave resonance spectra in (100) single-crystal nickel films is reported including the presence of surface spin wave modes. The variation of the spectrum with the angle between the applied magnetic field and the film normal is interpreted semiquantitatively in terms of Puszkarski's surface inhomogeneity models (1972). The value of the exchange constant D, is found to be 47+or-5*10-30 erg cm-2 for the applied field normal to the film surface.

Surface spin waves and surface spin arrangements in helical magnets

In order to investigate the nature of the spin arrangement in the surface of a semi-infinite helical magnet, we calculate both the surface spin-wave frequency spectra and the classical spin-ordering energies. We present detailed calculations for a (100) surface of a body-centered tetragonal lattice with nearest neighbor and next nearest neighbor exchange interactions (J1 and J2, which are both negative). The possibility that the exchange interactions in the surface (Js2) may differ from those in the bulk (J2) is taken into account. We find the following: In the case 0≳Js2≳J2, the surface spin-wave frequencies are real and positive, and hence the uniform helical spin arrangement is stable. On the other hand, in the case Js2&amp;lt;J2, there exist soft surface spin-wave modes, which indicate that the uniform helical spin arrangement is not stable. In the latter case, it is shown that a nonuniform spin arrangement, characterized by a rearrangement of spins in the surface, has a lower classical spin-ordering energy than the uniform state and hence is stable.

Effects of diffusion on magnetic excitations in films of yttrium iron garnet

We have investigated the effects of a diffusion located at the yttrium iron garnet-gadolinium gallium garnet (YIG-GdGaG) interface on spin-wave excitations. We calculate at ambient temperatures that a localized or surface spin-wave mode can be excited in chemical vapor deposited but not in liquid phase epitaxy (LPE) films of YIG. This localized state can be excited for the magnetic field applied parallel but not perpendicular to the film plane, in agreement with experimental observations. The dependence of spin-wave intensities on the direction of the magnetic field, observed in LPE films, is explained in terms of a nonuniform distribution of the cubic magnetic anisotropy field at the interface.