Optical Recording Aspects of rf Magnetron Sputtered Iron-Garnet Films

The intrinsic magneto-optical readout performance in reflection is calculated for bismuth and cobalt-substituted iron-garnet films on a multilayer interference mirror at 800-, 633-, 488-, and 420-nm wavelengths and is compared with that of a trilayer medium composed of an antireflection layer, a rare-earth transition-metal film, and a metallic mirror. It is found, when disregarding inhomogeneities, like irregular domain shape, ripple of the magnetic anisotropy, and surface roughness, that iron garnets are superior to rare-earth transition-metal films at blue to near-ultraviolet wavelengths if operated at thicknesses where optical interference occurs in the magnetic layer. Optical transmittance at these thicknesses is sufficiently high so that multilevel recording media can be conceived. In contrast, the optical absorption of rare-earth transition-metal alloys is much higher so that only thicknesses much above interference conditions are feasible, thus precluding them from multilevel recording. This comparative study is supplemented by calculating the magneto-optical performance in reflection of a recently reported multilayer medium composed of an antireflection coating and a periodically repeated sandwich of 4-Å Co and 9-Å Pt layers. In contrast to conventional rare-earth transition-metal films, the magneto-optical Kerr effects of this material do not degrade when decreasing the wavelength from 800 to 400 nm, but still do not reach the performance of bismuth-iron garnets in the green to ultraviolet spectrum. For the garnet system Y3--xBixFe5O12 the spectra of the real and imaginary parts of the diagonal and off-diagonal component of the dielectric tensor εij are reported in the range of photon energies between 1 and 5 eV, i.e., 1240- and 248-nm wavelengths and a bismuth concentration up x=1.4 Bi3+ atoms per garnet formula. In addition, the off-diagonal components ε′12 and ε″12 are parametrized in terms of paramagnetic optical transitions, taking the spectra for x=1.25 as a typical example. Furthermore, optical and magneto-optical spectra are presented for Co 2+- and Co3+- substituted iron garnets and barium hexaferrite BaFe12O19. Finally, the spectral dependence of the magneto-optical figure of merit 2ΘFp/α of (Y,Bi)3Fe5O12 and amorphous TbFe is compared. Furthermore, high-resolution transmission electron micrographs and x-ray double-crystal diffractograms are presented that elucidate the perfect epitaxial alignment of single-crystalline iron-garnet films and the columnar morphology of polycrystalline iron-garnet films prepared by rf magnetron sputtering. The initial nucleation period of polycrystalline garnet films can be influenced by low-energy ion bombardment for improving the film texture. Under favorable sputtering conditions single- and polycrystalline bismuth-iron garnet films develop a perpendicular magnetic anisotopy. It is not yet clear whether sputtered iron-garnet films can meet the critical requirements on magnetic wall coercivity and magnetic remanence

Growth, Morphology and Superconductivity of Epitaxial (RE)1\text{}_{1}Ba2\text{}_{2}Cu3\text{}_{3}O7−δ\text{}_{7-δ} Films on SrTiO3\text{}_{3} and NdGaO3\text{}_{3} Substrates

The growth of (RE)$\text{}_{1}$ Ba$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7-δ}$ (RE: Y, Nd) films on NdGaO$\text{}_{3}$ and SrTiO$\text{}_{3}$ substrates by ion-beam and dc-/rf-magnetron sputter deposition is discussed in the framework of growth kinetics, oxygen exchange, epitaxial relations, substrate crystal orientation, in-plane coherence, vicinal substrate cuts, overgrowth on steps, superconductor/insulator combinations, and patterning by ion-beam etching. The process conditions for ion-beam and magnetron sputter deposition are briefly outlined

A multi-layer process for the fabrication of HTSC flux transformers and SQUIDS

A multi-layer technology, based on YBaCuO as the superconducting material and SrTiO3 as the insulating material, is described. Patterning is performed by photolithography and Ar-ion-beam etching under fiat incidence. Using a resist bake-out prior to the etching, step angles in the patterned lower film of less than 20 degrees are obtained. Superconducting 10-turn thin-film coils have been fabricated with transition temperatures of up to 83 K and critical current densities at 77 K of 2*105 A cm-2. Furthermore we have fabricated a thin-film flux transformer and combined it in flip-chip configuration with a low-noise YBCO step-edge DC SQUID. We measured a magnetic field resolution of the complete magnetometer of 200 fT Hz-1/2 at 1 Hz, dominated by the SQUID noise itself

High- SQUID magnetometers for biomagnetic measurements

We have designed and fabricated three types of high- SQUID (superconducting quantum interference device) magnetometers based on step-edge Josephson junctions using three different concepts of coupling magnetic flux into the SQUID: (i) a single pickup loop galvanically coupled to the SQUID, (ii) a flux transformer inductively coupled to the SQUID and (iii) a multiloop pickup loop used directly as the SQUID inductance. On a substrate we achieved an effective flux capture area of and for the inductively coupled and multiloop devices, respectively. Due to the low white noise levels of for the inductively coupled magnetometer and for the multiloop device high quality magnetocardiograms were recorded inside a magnetically shielded room without signal averaging

SQUIDs aus Hoch-T_c-Supraleitern Abschlussbericht

In this research project low-noise SQUIDs (Superconducting Quantum Interference Devices) for biomagnetic measurements were made of high-Tc-superconductors. 1. YBaCuO films were prepared by ''off-axis''-sputtering and by a newly developed ionbeam sputter deposition technique. 2. The influence of the substrate material and its crystallographic orientation on the film properties was investigated systematically. 3. For film patterning Ar-plasma etching and Ar-ionbeam etching were used. Superconducting constrictions down to 200nm width were prepared. 4. Several concepts of Josephson junctions were investigated. The most successful one was the ''step-edge'' SQUID. Many SQUIDs have been prepared showing a reasonably large modulation depth at 77K (7.5 #mu#V). Using a bias-modulation technique a flat noise spectrum was obtained with a noise level of 70#mu##PHI#_0/#sq root#Hz at 77K. 5. A multilayer-technology was developed using insulating layers of SrTiO_3 with which superconducting coupling coils were realized. (orig.)In diesem Forschungsvorhaben wurden rauscharme SQUIDs (Superconducting Quantum Interference Devices) aus Hoch-Tc-Supraleitern fuer biomagnetische Messungen hergestellt. 1. Es wurden YBaCuO-Filme mit dem ''off-axis''-Sputterverfahren und mit der neu entwickelten Ionenstrahlsputter-Deposition hergestellt. 2. Es wurde der Einfluss vom Substratmaterial und dessen kristallographischer Orientierung auf die Schichteigenschaften systematisch untersucht. 3. Fuer die Mikrostrukturierung wurde Ar-Plasma-Aetzen und Ar-Ionenstrahl-Aetzen eingesetzt. Es gelang, supraleitende Bahnen bis zu einer kleinsten Breite von 200 nm herzustellen. 4. Es wurden verschiedene Konzepte zur Realisierung von Josephson-Kontakten untersucht. Am erfolgreichsten erwies sich das ''Stufen-Kontakt''-SQUID. Hier konnten viele SQUIDs hergestellt werden, die bis 77K eine relativ grosse Modulation (7.5 #mu#V) aufweisen. Mit Bias-Modulation konnte bei 77K ein flaches Rauschspektrum mit 70#mu##PHI#_0/#sq root#Hz gemessen werden. 5. Es wurde eine Mehrlagentechnologie mit isolierenden Zwischenlagen aus SrTiO_3 entwickelt und fuer supraleitende Einkoppelspulen eingesetzt. (orig.)Available from TIB Hannover: RN 3289(806)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

SQUID-Module aus Hoch-T_c-Supraleitern fuer die Magnetometrie Abschlussbericht

SIGLEAvailable from TIB Hannover: RN 3289(824)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Magnetokardiographiesystem aus Hoch-Tc-Supraleitern Abschlussbericht

Ziel dieses Forschungsvorhabens ist die Entwicklung eines Vielkanal-Magnetometers fuer die Kardiologie, welches mit SQUIDs aus Hochtemperatursupraleitern ausgestattet ist. Des weiteren soll die Abschirmkabine durch ein leichteres und preisguenstigeres Kompensationssystem ersetzt werdenA multi-channel magneotometer with high-Tc SQUIDs for magnetocardiography has been developed. Further developments focus on the screening component, which is to be designed as a much lighter and less expensive component for noise compensation. (orig./CB)SIGLEAvailable from TIB Hannover: RN 3289(836) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman