Sotaro Esho

Anomalous Magneto-optical Hysteresis Loops of Sputtered Gd-Co Films

Hysteresis loop anomaly in Gd-Co films has been studied by measuring magneto-optical Kerr loops at a temperature range from 20 to 60°C. Anomalous loops were observed at one surface of the films and in a certain temperature range. The other surface always gave normal loops. All the features of the observed anomalous loops can be explained by a magnetization gradient model along the film thickness.

Low Loss 1–2 GHz SAW Filters with Submicron Finger Period Electrodes

Low loss GHz SAW filters with submicron finger-period double electrodes have been developed. One was a 1 µm period 0.9 GHz filter with 5 dB insertion loss and the other a 0.5 µm period 1.9 GHz filter with 7 dB loss, both having three-transducer configurations on a 128° Y-X LiNbO3 substrate. These filters were realized by a new fabrication process, using direct wafer electron beam writing, two step mask transfer from electron resist PMMA to photoresist AZ-1350J and ion beam etching. The insertion loss was lowered mainly by optimizing ion beam etching conditions to decrease acoustic propagation losses due to electrode edge geometries, ion etched surface damages and electrode film absorption.

Optimum Thickness of MnBi Films for Magnetooptical Memory

Magnetic behavior of thermomagnetically written domains in MnBi films (400 A to 1200 A thick) has been studied. The written domains were circular in shape but became deformed and irregular with increasing film thickness. The circular domains of 1.5 microm in diameter were stable only in the films thinner than 700 A for writing and erasing processes. The stability of written domains can be explained by introducing measured wall coercivity values into a domain theory. The film wall coercivity was varied from 250 Oe to 800 Oe in inverse proportion to the film thickness.

Dynamic observation of thermomagnetic writing on MnBi films

Thermomagnetic writing on MnBi films was studied by dynamic observation on a change in a magnetization state using a two-beam method. As a writing laser beam increased in pulse duration, four writing characteristics were successively observed: I) nonwritable, II) writable without the first order phase transition, III) writable with the transition, and IV) decomposed. Observation of a nonmagnetic state in a writing cycle in II) revealed that the thermomagnetic writing is the extrapolated Curie point writing. The domain expansion phenomena observed in a writing cycle in II) are discussed based on a domain theory.

Optical and Magneto-Optical Properties of MnBi Films

For oriented MnBi films, the diagonal and off-diagonal components of the complex dielectric tensor were determined from optical and magneto-optical data measured in the 425 to 1000 nm wavelength range. The complex dielectric tensor indicates that several electronic transitions contributed from the magnetic electrons are located in the 600 to 1000 nm wavelength range, and may be responsible for the large Faraday rotation of MnBi films over this wide wavelength range. The Kerr rotations for s and p polarized waves were measured and calculated from the dielectric tensor as a function of the incident angle at 632.8 nm. The calculated results can explain the general behaviour of the dependence of the measured Kerr rotations on the incident angle.

New Organic Dye Medium For Ablative Optical Recording

An organic dye medium has been developed for diode-laser high-density recording. The new medium, having a single layer structure, can be recorded and played back by a laser diode through a substrate. It provides 54 dB signal to noise ratio in a 30KHz bandwidth at 2.5MHz carrier frequency. The medium shows excellent properties for long-term stability.

Intermediate Compounds in the Thin Films of Mn-Bi System

New birefringent compounds are found in films which are prepared by annealing double layers of successively evaporated Mn and Bi with various Mn to Bi ratios. The compounds are classified into three patterns by observation with a polarization microscope: needle-shaped, leaf-shaped and patched patterns which differ from a magnetic domain pattern in MnBi films. These patterns are observed in the films obtained from double layers with Mn to Bi starting atomic ratios, 0.8–1, 1–1.5 and 1.5–3, respectively. Electron probe microanalyses reveal that an Mn to Bi composition ratio of the leaf-shaped compound is about 0.5, and that of the patched compound is slightly greater than 1.