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180° and 90° domain walls in Bi-substituted [110] and [100] oriented garnet films with in-plane magnetization are studied by means of planar excitation-detection structures at microwave frequencies. New multiple resonance modes of single domain walls with very low linewidth (4.2 MHz) are observed at frequencies near 1 GHz. The resonances are excited by rf magnetic fields which are parallel or perpendicular to the wall plane. Resonance frequencies show a nonlinear dispersion dependence on the mode number. They decrease with an increasing static in-plane magnetic field normal to the wall plane. With decreasing film thickness the resonance frequencies increase. In addition the well known low-frequency resonances related to the wall translations or its flexural vibrations (Goldstone modes) are also observed in these samples.

The relaxation of 57Fe nuclei in yttrium iron garnet (YIG) is very sensitive to the way in which charge compensation is achieved in these magnetic insulators. Charge compensation becomes necessary either if nontrivalent impurities are incorporated in the garnet structure or in the presence of intrinsic defects. From measurements of the nuclear relaxation times T1 and T2 in epitaxial YIG films doped with small amounts of Ca, Si or Pb, we conclude that the relaxation behavior at low temperatures depends critically on the presence of certain intrinsic defects, namely Fe2+. These ions also increase the optical absorption in the near infrared.

A rigorous theory of parallel pump instability threshold of spin waves in ferromagnetic films is developed. Dipole and exchange interactions, the dipole-dipole hybridization of spin wave branches, and the magnetocrystalline and induced anisotropies are taken into account. Expressions for the parallel pump instability threshold are obtained in general form which can be used to calculate the threshold of a single ferromagnetic layer or a multilayered structure containing an arbitrary number of ferromagnetic films. The influences of the dipole-dipole hybridization of parametrically generated spin waves and of their nonreciprocal propagation properties on the threshold are discussed.

Yttrium-iron-garnet (YIG) films for magneto-optical applications are made by liquid phase epitaxy (LPE) from a melt containing Pb ions. In the course of annealing procedures Pb segregates on the surface of the YIG films. The evidence for and the temperature dependence of the segregation is studied by low energy ion scattering (ISS).

Spatial pattern formation in strongly driven ferromagnets has been predicted theoretically but not yet verified by experiment. We present an experimental set-up to excite the ferrimagnetic resonance of magnetic garnet films locally at high power levels. The spin precession is observed optically by means of Faraday rotation. Using special garnet films with very low saturation magnetization, we were able to observe the formation of spatial patterns.

The weak ferromagnet FeBO3 exhibits a strong dependence of the transverse sound velocity on the external magnetic field. This dependence has been measured for phonons up to the GHz region. The results can be explained satisfactorily by the interaction of the phonon and magnon dispersion branches.

Barium hexaferrite films have been grown by liquid phase epitaxy on Zr and Mg substituted Strontium hexagallate substrates. Continous films of 20 mm diameter have been obtained. The film surface exhibits terrace growth with a step height of about 10 nm. The saturation magnetization and anisotropy field as measured by static and FMR techniques are close to data of bulk crystals. An FMR linewidth of 45 Oe at 53 GHz was found for a 2.1 μm thick film.

Using special microwave structures, strong spin precessions can be excited locally in LPE garnet films by microwaves near the ferrimagnetic resonance frequency. As soon as the precession angle θ exceeds a critical value, the spins tip over creating a bubble domain. If the bubble is small compared with the excitation region, it is ejected out of this region along a spiral path. In the other case, the bubble is trapped at the excitation region and reaching another critical value of θ the spins again tip over, creating a ring domain. Single-ring domains can only be stabilized by the microwave induced spin precession inside the ring. Amplitude modulation of the microwaves leads to a corresponding radial oscillation of the ring. Stripe domains are forced to align either parallel or perpendicular to the gradient of the spin precession. At high bias fields a new type of domain is observed.

It is demonstrated that ferrimagnetic resonance can be applied to induce a dynamical conversion of optical modes in a magnetic garnet film. The fundamental and first‐harmonic Fourier components of the converted mode are measured as a function of frequency and bias field; a dynamical conversion efficiency of 2% is obtained. The amplitude of the first harmonic depends very critically on the orientation of the magnetization with respect to the film normal. The results are confirmed by calculations on the basis of Faraday rotation and Cotton–Mouton effect.

The radial oscillation of bubble lattices in LPE garnet films has been measured as a function of static fields applied perpendicular to the film or in the film plane, using a simple RF technique. While the dependence of the measured resonance frequency on the normal field can be described by theory, the measured frequency increases more rapidly with the in-plane field than calculated; this discrepancy is probably due to an incorrect theoretical dependence of the wall mass on the in-plane field.

In magnetic garnet films spatial minima or maxima of the spin precession are generated by special microwave structures. At these positions bubble domains can be trapped; at a minimum of the spin precession the diameter of a trapped bubble is smaller and at a maximum it is larger than that of a free bubble. This change of the bubble diameter is measured. The experimental results can be explained by a theoretical model which only takes into account the precession induced decrease of the static magnetization. Mit Hilfe spezieller Leitungsstrukturen fur Mikrowellen werden in magnetischen Granatfilmen raumliche Minima oder Maxima der Spinprazession erzeugt. An diesen Stellen konnen Bubble-domanen festgehalten werden; dabei ist der Durchmesser einer gefangenen Bubble an einem Minimum der Spinprazession kleiner, an einem Maximum dagegen groser als der einer freien Bubble. Diese Anderung des Bubbledurchmessers wird gemessen. Die experimentellen Ergebnisse lassen sich mit Hilfe eines theoretischen Modells erklaren, das nur die von der Spinprazession hervorgerufene Verringerung der statischen Magnetisierung berucksichtigt.

Propagation of optical modes in (110) oriented garnet films is calculated. Due to the in-plane anisotropy of these films the phase constants of the modes depend on the direction of propagation. It is shown that this effect can be applied for a fine adjustment of the phase matching between TE and TM modes which is necessary for mode conversion. The optical anisotropy of a (110) oriented garnet film is measured; it is sufficient to achieve phase matching. Die Ausbreitungsbedingungen optischer Moden in (110)-orientierten Granatfilmen werden berechnet. Die Phasenkonstanten der Moden hangen infolge der optischen Anisotropie von der Ausbreitungsrichtung in der Filmebene ab. Es wird gezeigt, das sich dieser Effekt fur eine Feinabstimmung der Phasenanpassung zwischen TE- und TM-Moden, die zur Modenkonversion notig ist, ausnutzen last. Fur einen (110) orientierten Granatfilm wird die optische Anisotropie gemessen; sie ist ausreichend, um Phasenanpassung zu erzielen.

Domain wall oscillations in magnetic garnet films have been observed in the stripe lattice and in the bubble lattice for applied in-plane magnetic fields approaching the saturation limit of the film. Observations are reported in (111) and (001) oriented films. An effective domain wall mass model is developed which allows the variation of the azimuthal angle of the spins in a moving wall when an in-plane field is applied in the plane of the wall. The new model gives results which are in much better agreement with the experimental results than previous models. Reasonable agreement is also observed between theory and experiment when the cubic anisotropy is included. Experimental evidence of the Hubert wall structure and its change for in-plane fields less than 8 M is also reported.

Magnetic bubble films exhibit a number of ferrimagnetic resonance modes due to the spatial variation of the anisotropy. The resonance frequencies have been measured as a function of the applied bias fieldH 0. In the lower field range the magnetization of the transient layer, which has negative anisotropy, is not yet parallel toH 0. In this range the resonance frequencies are shifted to higher values due to pinning effects. In films grown by the vertical dipping method an additional layer on top of the transient layer is observed within which the magnetization rotates from the direction in the transient layer to that of the bulk of the film. In films grown by horizontal dipping no such layer could be detected. Each ferrimagnetic resonance mode excites transverse elastic waves in the film due to the magnetoelastic interaction and thus gives rise to elastic resonances of the whole crystal, film and substrate. These elastic resonances lead to a fine-structure of the ferrimagnetic resonances. The observed fine-structure vanishes periodically with frequency and from this behaviour the thickness of the magnetic film and of the transient layer has been determined.

The wall resonance frequencies of bubble and stripe lattices in the hexagonal ferrites BaFe12O19 and PbFe12O19 have been measured as a function of crystal thickness and magnetic fields applied parallel and perpendicular to the c axis, which is oriented normal to the crystal surface. The dependence of the resonance frequencies on the normal field is in agreement with theory. For the dependence on the in‐plane field, however, a similar deviation between theory and experiment occurs, as is observed in garnet bubble materials; furthermore, the resonance frequencies increase stronger with decreasing thickness of the crystals than is predicted by theory.

Perpendicular ferrimagnetic resonance in (111) oriented epitaxial garnet films is excited by strong rf drive fields causing large foldover effects. The precession angle of the magnetization is derived from the measured change of Faraday rotation of linearly polarized light passing through the films. Precession angles of over 60° have been observed. Measurements of the steady‐state precession angles are in good agreement with calculations on the basis of Gilbert equations. The transient behavior of the precession, however, is slower than calculated. Conditions to achieve large precession angles are given.

Magnetoelastic excitations with a fine structure in the 50kHz range have been observed in the study of the domain wall resonance (DWR) in magnetic garnet thin films. DWR excites standing transverse elastic waves which have a resonance frequency given by f= nv 2d , where f is the frequency, n is an integer, v=3.5×10 5 cm/sec is the transversal velocity of the elastic wave, and d=0.05 cm is thickness of the film/substrate system. A fine structure associated with each of these modes has been identified as due to two dimensional bulk elastic waves by using a set of parallel microstrip lines. The dispersion relation of these elastic waves is ω 2 = v 2 ( k 2 1 + k 2 2 ), where ω is the radial frequency, k 1 and k 2 are the wave vectors in the orientation perpendicular and parallel to the sample surface respectively. In the case of k 1 ⪢k 2 , f= f 0 +v 2 k 2 2 f 0 , where f 0 is the resonance when k 2 =0. The experimental results are in excellent agreement with this model. A linear dispersion, observed when using a shorted slot-line structure, is understood as the excitation of three dimensional modes due to the complex structure of the slot-line and the sample geometry.

In this work the temperature dependence of the absorption of NaCl has been measured in the range from 77 to 370°K and at frequencies between 100 and 300 KMc (3÷1 mm wave-length). The measurements were performed with a grating spectrometer suited forMM-waves and a harmonic generator as radiation source. The experimental results are discussed on the basis of infrared dispersion theory which describes the absorption by two-phonon processes. Below 140°K they are consistent with the theoretical temperature dependence of those two phonon processes which should cause theMM-wave absorption. At higher temperatures higher order processes are indicated.

The infrared absorption due to localized vibrations of H− and D− ions in NaF and LiF is measured between 20 and 300 °K. The oscillator strengths are temperature independent. Measurements with uniaxial pressure show that the frequency of the local mode in NaF:H− is shifted by lattice distortions of the symmetry of Γ and Γ but not of Γ. In NaF:D−, LiF:H−, and LiF:D− two-phonon decays are allowed resulting in relatively large halfwidths at low temperatures. In NaF:H− a two-phonon decay is not possible and the halfwidth becomes smaller than the minimum spectral slit width of the grating spectrometer. The temperature dependence can be described by a scattering process in NaF:H− and by a composition of a scattering process with a two-phonon decay process in the other systems. The anharmonic frequency shift is calculated to a first approximation. In a simple density approximation the side band spectra can be described better by anharmonicity than by nonlinear dipole moments. Die Ultrarotabsorption lokalisierter Schwingungen von H−-und D−-Ionen in NaF und LiF wird zwischen 20 und 300 °K gemessen. Die Oszillatorenstarken sind temperaturunabhangig. Messungen mit uniaxialem Druck an NaF:H− zeigen, das die Frequenz der lokalisierten Schwingung durch Gitterverzerrungen der Symmetrien Γ und Γ, aber nicht durch Γ verschoben wird. In NaF:D−, LiF:H− und LiF:D− sind Zweiphononen-Zerfallsprozesse erlaubt, so das man bei tiefen Temperaturen relativ grose Halbswertsbreiten erhalt. In NaF:H− ist ein solcher Zerfall nicht moglich, und die Halbwertsbreite wird kleiner als die spektrale Spaltbreite des Gitterspektrometers. Der Temperaturverlauf kann in NaF:H− durch einen Streuprozes, in den anderen drei Systemen durch Uberlagerung eines Zweiphononen-Zerfallsprozesses mit einem Streuprozes erklart werden. Die anharmonische Frequenzverschiebung wird in erster Naherung berechnet. Mit einer einfachen Dichtenaherung konnen die Seitenbanden durch Anharmonizitat besser beschrieben werden als durch nichtlineare Dipolmomente.

A study on the horizontally LPE-grown La, Ga: YIG films is presented. With the spin wave resonance technique the ratio of the saturation magnetizations of the bulk and transient layer has been measured. The average saturation magnetization was determined by means of a vibrating sample magnetometer and the Ga concentration by x-ray fluorescence analysis. These data are compared with the growth rates of both the transient and the bulk layer. A systematic dependence of the magnetization on the growth rate is found.

Magnetic bubble and ring domains are generated in LPE garnet films by locally exciting spin precession near the ferrimagentic resonance frequency at high microwave power densities. Due to the spin precession, radial and azimuthal forces act on the bubbles. The radii of the ring domains vary with the microwave power and the bias field. The stability range of these domains extends over a bias field range of about 0.18 times 4πMs. The dynamic behavior of the ring domains could be studied by amplitude modulation of the microwaves.

Among the various synthetic fuels that can be used either as blending stocks, as substitute for crude oil derived gasoline or as fuel for Diesel engines alcohols derived from methane are receiving special attention. The Institute of Reactor Components at the Nuclear Research Centre Julich has started a research program concerning methane and alcohols. The examination of their potential as a synthetic liquid energy carrier with regard to economical production and ecologically beneficial combustion behaviour is the aim of this programme.

In LPE garnet films strong spin precessions can be excited locally by microwaves near the ferrimagnetic resonance frequency. When the precession angle ϑ exceeds a critical value the spins tip over and create a bubble within which the spins keep on precessing due to the microwave excitation. With further increasing ϑ a second critical value is reached where the spins again tip over and create a bubble within the the first one, i.e. a ring domain. Continuing in this way systems of many concentric rings can be generated which are stable even in the case of vanishing microwave power. However, single ring domains in films of low coercivity can only be stabilized by microwaves. To a first approximation the stabilizing forces on these domains are due to the precession induced change of the dc magnetization inside the ring.If the microwave stabilizing a single ring domain are amplitude modulated a corresponding radial motion of the ring is induced. From this motion one can derive the eigenfrequency and velocity o...

The infrared absorption of H-ions in LiF and H- and D-ions in NaF has been measured. The energetic positions of the local modes in NaF:D- and LiF:H- allow 2-phonon decay processes as indicated by the variation of the absorption bandwidth at low temperatures. In NaF side bands have been observed.