ALBERT

Notes: We communicate a detailed study of the epitaxial growth of CeO2 on MgO. The key feature of the growth is the dependence of the in-plane orientation of the CeO2 epitaxial layer on the MgO surface morphology. Atomic force microscopic (AFM) measurements, x-ray analyses, as well as high-resolution transmission electron microscopy (HRTEM) investigations reveal that on rough substrates a cube-on-cube growth of CeO2 on MgO occurs while on smooth substrates the CeO2 unit cell is rotated around the surface normal by 45° with respect to the MgO unit cell when the deposition rate is low (∼0.3 A(ring)/s) during the first stages of growth. This growth mechanism can be used for a defined fabrication of 45° grain boundaries in the CeO2 layer by controlling the surface roughness of the MgO substrate. This report demonstrates that these 45° grain boundaries may be used to fabricate YBa2Cu3O7−x Josephson junctions. © 1995 American Institute of Physics.

Notes: The static and spin wave properties of regular square lattices of magnetic dots of 0.5–2 μm dot diameter and 1–4 μm periodicity patterned in permalloy films have been investigated by Brillouin light scattering. The samples have been structured using x-ray lithography and ion beam etching. The Brillouin light scattering spectra reveal both surface and bulk spin wave modes. The spin wave frequencies can be well described taking into account the demagnetization factor of each single dot. For the samples with smallest dot separation of 0.1 μm a fourfold in-plane magnetic anisotropy with the easy axis directed along the pattern diagonal is observed, indicating anisotropic coupling between the dots. © 1997 American Institute of Physics.

Notes: The switching dynamics of magnetic tunnel junctions has been studied by means of time resolved magneto-optic Kerr magnetometry. Magnetic field pulses as short as 250 ps are found to be sufficiently long to switch the storage content of the element. In order to test the write endurance the magnetization of one single element has been reversed 1011 times. Shortly after the initialization of the hard magnetic layer the magnetization reversal process of the soft magnetic layer remains unchanged, indicating that no further degradation of the pinned layer comes into effect. © 2002 American Institute of Physics.

Notes: The photoluminescence spectrum of melt-grown GaSe single crystals was investigated with a confocal Raman microscope equipped with a HeNe laser. Three luminescence bands of different intensity were observed, which are mainly located to the blue of the laser line. The luminescence signals show a quadratic dependence on excitation intensity. The effect is interpreted as second-harmonic generation in the strongly optically nonlinear material followed by the excitation of electrons into the conduction band and luminescence emission from direct-gap Wannier excitons. The relative intensities of the three luminescence peaks exhibit a spatial variation on the crystal surface, which was mapped with the confocal microscope. Possible explanations of this effect are discussed. In an external electric field the luminescence shows a strong increase and a quadratic redshift, whose magnitude is consistent with the Franz–Keldysh mechanism. © 2002 American Institute of Physics.

Notes: A new advanced space- and time-resolved Brillouin light scattering technique is used to study diffraction of two-dimensional beams and pulses of dipolar spin waves excited by strip-line antennas in tangentially magnetized garnet films. The technique is an effective tool for investigations of two-dimensional spin wave propagation with high spatial and temporal resolution. Nonlinear effects such as stationary and nonstationary self-focusing are investigated in detail. It is shown that nonlinear diffraction of a stationary backward volume magnetostatic wave (BVMSW) beam, having a finite transverse aperture, leads to self-focusing of the beam at one spatial point. Diffraction of a finite-duration (nonstationary) BVMSW pulse leads to space–time self-focusing and formation of a strongly localized two-dimensional wave packet (spin wave bullet). © 2000 American Institute of Physics.

Notes: We report results of the switching properties of thin magnetic films described by Stoner-like magnetic blocks subject to ultrashort, laterally localized magnetic field pulses, obtained by numerical investigations. Perpendicularly magnetized films exhibit a magnetization reversal due to a 4 ps magnetic field pulse, which can be explained with a coherent rotation model. Although the magnetic field pulse is short compared to the ferromagnetic resonance precession time, the time needed for the relaxation of the magnetization to the equilibrium state is rather large. In addition, we show numerical results for the magnetization reversal of an in-plane magnetized sample with uniaxial in-plane anisotropy. © 2000 American Institute of Physics.

Notes: We report on investigations of the crystallographic structure and the magnetic anisotropies of epitaxial iron films deposited onto periodically stepped Ag(001) surfaces using low energy electron diffraction, x-ray diffraction, second harmonic generation (SHG), as well as the Brillouin light scattering (BLS) technique. The focus of the present study lies on the interrelation between the surface morphology of the buffer layers and the magnetic properties of the Fe films, epitaxially grown onto them. Especially the symmetry breaking at the atomic steps is found to create an uniaxial magnetic anisotropy measured by BLS and a very strong anisotropic signal in magnetic SHG. © 2000 American Institute of Physics.

Notes: We report on the exchange bias effect as a function of the in-plane direction of the applied field in twofold symmetric, epitaxial Ni80Fe20/Fe50Mn50 bilayers grown on Cu(110) single-crystal substrates. An enhancement of the exchange bias field, Heb, up to a factor of 2 is observed if the external field is nearly, but not fully aligned perpendicular to the symmetry direction of the exchange bias field. From the measurement of the exchange bias field as a function of the in-plane angle of the applied field, the unidirectional, uniaxial and fourfold anisotropy contributions are determined with high precision. The symmetry direction of the unidirectional anisotropy switches with increasing NiFe thickness from [11¯0] to [001]. © 1999 American Institute of Physics.

Notes: Static and dynamic magnetic properties of epitaxial Fe(001) films with Pd overlayers have been measured by means of Brillouin light scattering and magneto-optic Kerr effect magnetometry. From low energy electron diffraction studies, the initial growth of Pd [dPd〈2 monolayer (ML)] is identified as a self-formation process of quasione-dimensional Pd structures. Auger electron spectroscopy examinations proved that for dPd≥2 ML the Pd overlayers cover the Fe films almost completely. The measured frequencies of the dipolar spin wave mode and the derived anisotropy constants show a linear change with increasing dPd up to 5 ML with following saturation. The M(H) curves show pronounced anomalies in the coercive field for dPd〈2 ML accompanied by large tails in the hysteresis loops. The results are interpreted as a strong pinning of domain walls caused by large local changes in the surface anisotropy due to the inhomogeneous Pd cover layer in this regime. © 1997 American Institute of Physics.

Notes: We have investigated the propagation of surface and backward volume spin waves (BVSW) with the in-plane wavevector k(parallel)=10–900 cm−1 excited by microwaves in YIG and Lu2.04Bi0.96Fe5O12 (LBIG) films with the film thicknesses 5 and 1.5 μm, respectively. In all cases the magnetization and k(parallel) were in the film plane. The frequencies of the spin wave excitations as well as the spatial distribution of their intensities in the linear and in the nonlinear excitation regime were measured by means of a fully automated, high-stabilization, small-angle Brillouin light scattering (BLS) setup with a spatial resolution of 30 μm. It is well known1 that in the case of BVSW modes, the Lighthill criterion2 for modulational instability is fulfilled for both the longitudinal and the transverse perturbations of the initially constant-amplitude wave beam. Therefore, this mode is very much suitable for the investigation of the evolution of a plane-front, constant-amplitude initial beam, and for a direct experimental study of two-dimensional nonlinear diffraction effects of the beam leading to self-focusing. The garnet films with in-plane dimensions of 2×10 mm2 were grown by liquid phase epitaxy onto a single crystalline (111)-oriented gallium gadolinium garnet substrate. Two strip antennas, 35 μm wide and situated at the ends of the films, were used for the excitation of the spin waves and for monitoring. The working frequency was 8.10 GHz. Special efforts were taken to minimize the beam divergence due to the finite length of the input antenna. For all nonlinear studies the initial angular beam divergence was not larger than aitch-thetamax=0.05 rad. In the linear regime the attenuation factor was measured, and the reflection of the spin waves from the sample boundaries was studied. We also observed the interference between the two lowest order lateral modes having different initial spatial distributions of the magnetization. The BLS technique was shown to provide a signal to noise ratio exceeding 60 dB. In the nonlinear regime the propagation of the BVSW mode was thoroughly investigated. We have found clear evidence for the self-focusing effect, which exists in a narrow interval of input powers. In these studies overheating of the sample by the microwave power was carefully avoided by using an intermittent source of maximum average power of 100 mW working at a frequency of 4 kHz. That allowed us to claim that the observed focusing of the spin waves was not an artifact caused by sample heating. The distance between the focusing maximum and the antenna was 1.5 mm for LBIG sample and 6 mm for YIG sample. These values are in a good agreement with our theoretical calculations, if one takes into account the thicknesses of the films. For a comparison of the observed values of the width and the length of the focusing spot and their dependence on the microwave power with the theory, more numerical calculations are needed. Our results demonstrate the wide applicability of an advanced combined microwave-BLS technique for a two-dimensional mapping of the spin wave amplitudes in the media. © 1997 American Institute of Physics.