Magneto-optical Thin Films Research Articles

Magneto-optic recording materials with direct overwrite capability

The possibility of achieving direct overwrite capability in magneto-optic thin films is demonstrated. By using films having a compensation temperature tens of degrees higher than the ambient temperature, the demagnetizing field can effectively be used as a bias field for thermomagnetic writing in which writing and erasing of domains are accomplished in the absence of a magnetic field. A read-before-write scheme is proposed to facilitate the write/erase laser trigger signal to perform overwriting in real time.

Magneto-optic waveguide isolators based on laser annealed (Bi, Ga) YIG films

To overcome the effects of linear birefringence which limits the Faraday rotation achievable in magneto-optic thin film waveguides, a novel geometrical pattern of Faraday effect reversals has been designed. This pattern of P/2 segments followed by a P/4 segment where P is the birefringent period, has been built permanently into a (Bi,Ga)YIG film, with composition close to the compensation point, by laser annealing. This film provides nonreciprocal rotation of ±45° for light of wavelength 1.45 μm with an extinction ratio of 500 to 1, corresponding to 27 db of isolation.

A design for a nonreciprocal phase shifter

A design is described for a nonreciprocal phase shifter, which is the key element in the constitution of a Mach-Zehnder interferometric isolator consisting of a magneto-optical channel waveguide. A four-layered structure waveguide is dealt with in which a cover layer having a larger refractive index than that of the film is placed on the magneto-optic thin film; it is revealed that the phase shifter length can be shortened by up to 6 mm at the 1.15 μm wavelength, which is half the length of a nonreciprocal phase shifter constructed of a three-layered waveguide without a large refractive index cover layer. Two types of channel waveguides are investigated: a rib waveguide and a strip-loaded waveguide; they are found to have the same phase shifter length for the optimum condition.

New magneto-optic thin films for storage application

A new magneto-optic thin film having a composition defined by Mnx(Cu1−y′Niy′)yBiz, where x+y+z=1, 0.15?x?0.70, 0.10?y?0.55, 0.11?z⩽0.55, and 0<y′<1, was prepared by vacuum deposition. In this composition range the film has a Curie point between 100 and 200 °C and satisfactorily large magneto-optic figures of merit. It is stable against moisture. The maximum value of the magneto-optic figure of merit 2F/α is 1.1 deg for a wavelength of 6328 Å, where F is the specific Faraday rotation and α is the absorption coefficient. The hysteretic characteristics of the film can be improved by adding Ti, V, or Cr. The film is suitable for a magneto-optic storage medium.

Advanced Optical Storage Techniques for Computers

The growing demand for data storage in computing systems has stimulated the investigation of optical memory techniques because they offer a potential improvement in packing density of about two orders of magnitude over the apparent limits of conventional magnetic storage techniques. Physical properties and optical memory characteristics of magnetooptic thin-films of manganese bismuth have been investigated with regard to both bit-oriented and holographic memories. All the required technology for design of a bit-oriented memory appears to be available, but several key components required for a holographic memory still remain to be developed.

Experimental studies of magnetooptical kerr readout SNR

Characteristics of holography using binary photosensitive materials were investigated by analytical calculations and computer simulations in relation to the hologram recording conditions. It was concluded that by choosing proper intensities of object beam and reference beam for the threshold of the photoresponse, some degree of fidelity can be attained in the reconstructed images. It was also concluded that in the holographic memory where a page composer of a bit array is used, the number of the bits of the array should be limited to a small number (say 10 to 20 for one dimension) to get a clear distinguishability between 1 and 0. The above results are applicable to the holographic recording on magnetooptic thin films which are more or less binary in their photoresponse.

1144. The effect of antimony in magneto-optic thin films on manganese bismuth base. I. Film preparation and studies on the formation process: H Schroder et al, phys stat sol (a), 5 (1), April 1971, 169–175.

1144. The effect of antimony in magneto-optic thin films on manganese bismuth base. I. Film preparation and studies on the formation process: H Schroder et al, phys stat sol (a), 5 (1), April 1971, 169–175.

The effect of antimony in magneto-optic thin films on manganese bismuth base. II. Measurements of some magnetic and magneto-optic properties

The angle φF of the specific magneto-optic Faraday rotation and the coercivity of MnBi1−xSbx ferromagnetic thin films were determined by measuring the hysteresis loops using a magneto-optic method. At the wavelength 560 nm, the angle φF which is proportional to saturation magnetization decreases from about 6 × 105 degrees cm−1 to 0, whereas the coercivity Hc increases when x changes from 0.005 to 0.15. The wavelength dependence of φF was measured in the visible region of the spectrum. Die spezifische magneto-optische Faraday-Drehung φF und die Koerzitivkraft dünner ferromagnetischer MnBi1−xSbx-Schichten wurden bestimmt, indem die Hystereseschleifen auf magneto-optischem Wege aufgenommen wurden. Bei einer Wellenlänge von 560 nm nimmt die spezifische Faraday-Drehung φF, die der Sättigungsmagnetisierung proportional ist, von etwa 6 × 105 Grad cm−1 auf 0 ab, wenn x von 0,005 auf 0,15 steigt. Dagegen nimmt die Koerzitivkraft mit steigendem x zu. Die Wellenlängenäbhängigkeit von φF wurde für den sichtbaren Spektralbereich bestimmt.

The effect of antimony in magneto-optic thin films on manganese bismuth base. I. Film preparation and studies on the formation process

By adding antimony the system MnBi is extended to a three-component one. Using Sb concentrations not exceeding a critical value one gets facilitated conditions for preparation of magneto-optic thin films of the B8 structure with preferred orientations of the c-axis. Thereby a number of advantages could be obtained, compared with “pure” manganese bismuth films, e.g. relatively low formation temperatures and short formation times (in the order of 200 °C and 1 h, respectively), excellent film homogeneity, use of amorphous substrates instead of epitaxial materials. Films with surface protective layers of good quality show no significant difference whether the thermal formation of the vacuum-deposited three-layer-systems BiSbMn takes place in vacuum or in air. The effect of antimony additions to manganese bismuth has been demonstrated by observations chiefly obtained in a heat stage microscope. The results of these investigations are reported. Durch Zusatz von Antimon wurde das System MnBi zu einem Dreikomponentensystem erweitert. Die Herstellung magneto-optischer Schichten vom B8-Typ mit bevorzugter Orientierung der c-Achsen wird hierdurch wesentlich erleichtert, sofern eine kritische Antimon-Grenzkonzentration nicht uberschritten wird. Im Vergleich zu „reinen” Mangan-Wismut-Schichten zeigen sich z. B. folgende Vorteile: niedrigere Formierungstemperaturen und kurzere Formierungszeiten (etwa 200 °C bzw. 1 Stunde), ausgezeichnete Homogenitat der Filme, Moglichkeit der Verwendung amorpher Substrate anstelle epitaxialer Materialien. Wenn die durch Vakuumbedampfung hergestellten dreilagigen Ausgangsschichten BiSbMn mit Oberflachendeckschichten hoher Qualitat geschutzt werden, kann die nachfolgende thermische Formierung sowohl in Vakuum als auch in Luft ausgefuhrt werden. Der Einflus von Antimonzusatzen zu Mangan–Wismut-Schichten wurde in erster Linie mit einem Heiztischmikroskop verfolgt. Uber die erhaltenen Ergebnisse wird berichtet.

The effect of the demagnetizing field on Curie-point writing in magneto-optic thin films of MnBi

The effect of the demagnetizing field on Curie-point writing in magneto-optic thin films of MnBi