Magneto-optical memory element

Abstract

A magneto-optical memory element has a multi-layer construction in the order from a side first receiving light from a light-source which includes a first transparent dielectric film, a rare earth transition metal alloy film, a second transparent dielectric film and a reflective film. The magneto-optical device uses circular dichroism effect of a magnetic mater for reading information. The rare earth transition metal alloy film has a refractive index represented by n±Δn wherein n=3.2-3.55i and Δn=0.05-0.03i. The thickness of film is about 18 to 46 nm. The second transparent dielectric film has a refractive index of 2.0±0.2 and a film thickness of 80 to 108 nm.

What is claimed is: 
     
       1. A magneto-optical memory element having a multi-layer construction and a magnetic material to produce a circular dichroism effect, comprising: a first transparent dielectric film;   a rare earth transition metal alloy film positioned on said first transparent dielectric film;   a second transparent dielectric film positioned on said rare earth transition metal alloy film; and   a reflective film positioned on said second transparent dielectric film;   said rare earth transition metal alloy film having a refractive index represented by n±Δn wherein n=3.2-3.55i and Δn=0.05-0.03i;   said rare earth transition metal alloy film having a film thickness of 18 to 46 nm;   said second transparent dielectric film having a refractive index of 2.0±0.2 and a film thickness of 80 to 108 nm. .Iadd.   
     
     
       2.  In a magneto-optical memory element having a multi-layer construction comprising in sequence from a side on which light is incident a first transparent dielectric film, a rare earth transition metal alloy film, a second transparent dielectric film and a reflective film, the improvement wherein circular dichroism effects of the rare earth metal alloy transition film are used for reading information, said rare earth transition metal alloy film has a refractive index represented by n±ΔN wherein n=3.2-3.55i and Δn=0.05-0.03i and a thickness of 18 to 46 nm, and said second transparent dielectric film has a refractive index of 2.0±0.2 and a thickness of 80 to 108 nm. .Iaddend..Iadd.3. A magneto-optical memory element according to claim 2, in combination with an optical system including a semiconductor laser for directing light onto said magneto-optical memory element, and a light intensity detector for receiving light emitted by said magneto-optical memory element. .Iaddend..Iadd.4. A magneto-optical memory element according to claim 2, in combination with an optical system including means for directing circularly polarized light onto said element, and a light intensity detector for receiving light emitted by said magneto-optical memory element. .Iaddend..Iadd.5. A magneto-optical memory element according to claim 2, in combination with an optical system including a quarter wavelength plate, a semiconductor laser for directing light through said plate onto said element, and a light intensity detector for receiving light emitted by said magneto-optical memory element. .Iaddend..Iadd.6. A magneto-optical memory element according to claim 2, in combination with an optical system including a semiconductor laser for directing light onto said element, and a light intensity detector for receiving light emitted by said magneto-optical memory element, including means for transmitting said emitted light directly onto said light intensity detector. .Iaddend..Iadd.7. An optical reading apparatus comprising:   semiconductor laser means for emitting linear polarized light;   means for changing the linear polarized light emitted by the laser means to circularly polarized light;   a magneto-optical memory element for changing the light intensity of circularly polarized light from the laser means incident thereon in accordance with information stored therein and reflecting the light so changed, said magneto-optical memory element having a multi-layer construction comprising in sequence from a side on which light is incident a transparent substrate, a first transparent dielectric film, a rare earth transition metal alloy film, a second transparent dielectric film and a reflective film, the improvement wherein said second transparent dielectric film has a film thickness of 80 to 108 nm; and   detector means for detecting the light intensity of the circularly polarized light reflected from the magneto-optical memory element, said reading apparatus not including a polarization analyzer for analyzing the circularly polarized light detected by said detector means.   
     
     
        .Iaddend..Iadd..  The apparatus of claim 7 wherein said detector means detects said light intensity reflected from said magneto-optical memory element without regard to the direction of any linearly polarized light. .Iaddend..Iadd.9. The apparatus of claim 7 or 8 wherein said means for changing the linear polarized light to circularly polarized light 
     
     
        comprises a 1/4 wavelength plate. .Iaddend..Iadd.10.  An optical reading apparatus comprising: semiconductor laser means for emitting linear polarized light;   means for changing the linear polarized light emitted by the laser means to circularly polarized light;   a magneto-optical memory element for changing the light intensity of circularly polarized light from the laser means incident thereon in accordance with information stored therein and reflecting the light so changed; and   detector means for detecting the light intensity of the circularly polarized light reflected from the magneto-optical memory element, said reading apparatus not including a polarization analyzer for analyzing the circularly polarized light detected by said detector means. .Iaddend..Iadd.11. The apparatus of claim 10 wherein said detector means detects said light intensity reflected from said magneto-optical memory element without regard to the direction of any linearly polarized light. .Iaddend..Iadd.12. The apparatus of claim 10 or 11 wherein said means for changing the linear polarized light to circularly polarized light comprises a 1/4 wavelength plate. .Iaddend..Iadd.13. An optical reading apparatus consisting essentially of:   semiconductor laser means for emitting linear polarized light;   means for changing the linear polarized light emitted by the laser means to circularly polarized light;   a magneto-optical memory element for changing the light intensity of circularly polarized light from the laser means incident thereon in accordance with information stored therein and reflecting the light so changed, said magneto-optical memory element having a multi-layer construction comprising in sequence from a side on which light is incident a transparent substrate, a first transparent dielectric film, a rare earth transition metal alloy film, a second transparent dielectric film and a reflective film, the improvement wherein said second transparent dielectric film has a film thickness of 80 to 108 nm; and   detector means for detecting the light intensity of the circularly polarized light reflected from the magneto-optical memory element, said reading apparatus not including a polarization analyzer for analyzing the circularly polarized light detected by said detector means.   
     
     
        .Iaddend..Iadd.4.  The apparatus of claim 13 wherein said detector means detects said light intensity reflected from said magneto-optical memory element without regard to the direction of any linearly polarized light. .Iaddend..Iadd.15. The apparatus of claim 13 or 14 wherein said means for changing the linear polarized light to circularly polarized light comprises a 1/4 wavelength plate. .Iaddend..Iadd.16. An optical reading apparatus consisting essentially of: semiconductor laser means for emitting linear polarized light;   means for changing the linear polarized light emitted by the laser means to circularly polarized light;   a magneto-optical memory element for changing the light intensity of circularly polarized light from the laser means incident thereon in accordance with information stored therein and reflecting the light so changed; and   detector means for detecting the light intensity of the circularly polarized light reflected from the magneto-optical memory element, said reading apparatus not including a polarization analyzer for analyzing the circularly polarized light detected by said detector means.   
     
     
        .Iaddend..Iadd.7.  The apparatus of claim 16 wherein said detector means detects said light intensity reflected from said magneto-optical memory element without regard to the direction of any linearly polarized light. .Iaddend..Iadd.18. The apparatus of claim 16 or 17 wherein said means for changing the linear polarized light to circularly polarized light comprises a 1/4 wavelength plate. .Iaddend.