Jens-Peter Krumme

Optical and magneto‐optical tensor spectra of bismuth‐substituted yttrium‐iron‐garnet films

We report on the complete dielectric tensor spectra of Y3−xBixFe5O12 with 0≤x≤1.42 in the photon energy range 1≤ℏω(eV)≤4.8, i.e., 1240–248 nm wavelength. In an attempt to identify the involved optical transitions we have (i) parametrized these spectra in terms of Gaussian (e‘11 spectra) and diamagnetic or paramagnetic (e’12 and e‘12 spectra) line shapes, and (ii) come up with a set of coefficients of a cubic interpolation polynomial for each spectral ‘‘line’’ from which any of the n, α, ΘF, eF, ΘK, eK, e’11, e‘11, e’12, e‘12 spectra can be calculated for any bismuth substitution in the above compositional and spectral range. It is found that such a line‐shape analysis is not unique and requires physical knowledge on the optical excitations involved which, however, is still incomplete for iron garnets.

Energy distribution of negative O− and OH− ions emitted from YBaCuO and iron garnet targets by dc and rf magnetron sputtering

Energy‐dispersive mass spectrometry has been used to analyze the energy distribution of O− and OH− species ejected from YBaCuO and iron‐garnet targets by Ar+, Kr+, and Xe+ bombardment in H2‐ and in O2‐doped dc and rf magnetron plasmas at 0.05–4.2 Pa pressure. The orifice of the plasma monitor was at 70 mm from the erosion groove underneath the plasma ring. The energy spectra of O− and OH− ions are found to exhibit two major peaks: a sharp one at typically 20 eV termed A and a sharp (dc case) or broad (rf case) peak termed B at higher energies. Peak‐A ions may be formed near the edge of the cathode sheath by electron attachment to sputtered neutral oxygen atoms accelerated in the remaining potential gradient of the sheath. Peak‐B ions are shown to be accelerated from the target surface to kinetic energies given by the potential gradient across the cathode sheath. In the case of rf magnetron plasmas the total flux of O− and OH− ions associated with the peak B steeply increases with pressure up to ∼0.6 Pa fo...

Bismuth-substituted iron garnet films prepared by RF diode sputtering

Single-phase, magnetically uniaxial Gd 3-x Bi x Fe 5-y Al y O 12 films have been prepared by RF diode sputtering with RF substrate bias on single-crystal (Gd,Ca,Mg) 3 (Ga,Zr) 5 O 12 and amorphous substrates. Epitaxial growth is observed by annealing of amorphous films for lattice misfits <0.03A (tensile stress). Intrinsic properties, such as lattice constant, saturation magnetization, and polar magnetooptic effects, compare well with liquid-phase epitaxial films of equal composition. Film imperfections originating from particles expelled from the ceramic targets cause some optical loss, increased coercivity and increased linewidth in X-ray diffraction.

Ferrimagnetic garnet films for magnetooptic information storage

Reversible magnetooptic memories are believed to compete favorably with magnetic bubble devices and CCDs if economic low-power light sources can be used. For optical information storage at data rates of >106bit/s and blocks of 103bit, memory materials are required exhibiting an optical recording sensitivity on the order of the photographic plate. The presented contribution outlines the recently proposed concept of a magnetooptic/photoconductive sandwich, called MOPS, and shows that certain ferrimagnetic garnet compositions can especially be adapted to such applications.

Ion-beam etching of groove patterns into garnet films

The technique of ion-beam milling is applied to the structuring of garnet layers. Rf-sputtered titanium is found to be an appropriate masking material as its sputter etch rate is small and almost independent from the angle of incidence of the ion beam. In contrast, the garnet has a prominent etch rate angular dependence. The optimal conditions for the generation of grooves in garnet layers, masked by rf-sputtered Ti, are reported. By applying this technique, a well-resolved mosaic pattern of 20 μm periodicity and 5.5 μm depth has been formed in an LPE iron garnet film of 5 μm thickness.

Critical assessment and modification of Robinson's method for the ellipsometric investigation of thin film materials

Abstract Local optical properties of thin film materials can be easily studied using an ellipsometric method devised by Robinson. We have modified the optical components and measuring technique and investigated some critical parameters limiting the accuracy of this method. The analysis of the state of polarization, i.e. azimuth and ellipticity, of the beam emerging from the sample is exclusively based on the measurement of azimuths. By means of modulating the beam azimuth with a Faraday cell and using either a lock-in technique or an X–Y oscilloscope display for detection a very sensitive measurement of the beam polarization is possible. We have evaluated the beam ellipticity both for small and large azimuthal angles, and have used the Poincare sphere for the graphical representation of all measuring procedures. To eliminate depolarization by reflection all optical components, with emphasis on the wave plate and non-birefringent collimating lens, have been anti-reflection coated. Experimentally an absolute accuracy of 10 −2 degrees was achieved in the determination of ellipticity and azimuth.

Sputter-emission of negative and neutral mon-atomic oxygen from YBCO targets

In this article the production and energy distribution of negatively charged atomic oxygen O- in dc- and rf- magnetron sputtering are discussed based on recent work from other laboratories and our own. It is shown that a majority of these energetic secondary O- ions originate from the target surface and that their flux and kinetic-energy distribution are related to the target-sheath voltage, the energy distribution of the primary sputter-ions, such as Ar+, and collisional losses of the Ar+ and O- ions when traversing the target sheath. Factors affecting the yield of O- ions, such as target composition, dc- or rf-sheath, primary-ion mass, and oxygen and hydrogen admixture to the sputter-gas are briefly touched.