Magneto-optical recording medium

Abstract

Disclosed are magneto-optical recording media comprising at least a reflection layer, a recording layer and a dielectric layer laminated on a substrate in this order, wherein the thickness of the dielectric layer is not less than 140 nm or wherein the dielectric layer is provided by the lamination of upper dielectric layer and lower dielectric layer in which the thermal conductivity of the upper dielectric layer is higher than that of the lower dielectric layer. By arranging the thickness of the dielectric layer in a specific range, the surface roughness of a media in not more than 1.5 nm, and providing a reflection layer composed of a noble metal alloy, achieved is a magneto-optical recording medium able to record constantly in near-field magneto-optical recording, suitable for narrow track pitch, and having excellent SNR, resolution, and recording sensitivity.

1 . A magneto-optical recording medium characterized in a plurality of layers comprising at least a reflection layer, a recording layer and a dielectric layer laminated on a substrate in the above order, wherein the thickness of said dielectric layer is not less than 140 nm and not more than 1,000 nm.  
     
     
         2 . The magneto-optical recording medium according to  claim 1 , in which the thermal insulating ratio of said dielectric layer (d 3 /ρ) and the thermal diffusion ratio of said dielectric layer (ρd 3 ) satisfy a relationship represented by  
         d   3 /ρ≧3×10 −11    cm   2   Ks/erg,  and ρ d   3 ≧1.5  erg/Ks,    
       wherein, ρ represents the thermal conductivity of said dielectric layer and d 3  represents the thickness of said dielectric layer.  
     
     
         3 . The magneto-optical recording medium according to  claim 1 , in which the surface roughness (Ra) (the centerline average roughness of a surface) of said substrate is not more than 0.5 nm.  
     
     
         4 . The magneto-optical recording medium according to  claim 1 , in which the surface roughness (Ra) of said dielectric layer is not more than 1.5 nm.  
     
     
         5 . The magneto-optical recording medium according to  claim 1 , in which the refractive index of said dielectric layer (n 3 ), the thickness of said dielectric layer (d 3 ) and the wavelength of a reproducing laser (λ) satisfy a relationship represented by  
       0.6≦( d   3   ·n   3 )/λ≦0.9, or 1.2≦( d   3   ·n   3 )/λ≦1.5.  
     
     
         6 . The magneto-optical recording medium according to  claim 1 , in which said dielectric layer is composed of two layers including a primary dielectric layer (refractive index; n 31 , thickness; d 31 ) having a refractive index of not less than 1.7, and diamond-like carbon layer or silicon dioxide layer (refractive index; n 32 , thickness; d 32 ), wherein the refractive indexes and the thickness of these layers satisfy a relationship represented by  
       1 nm≦d 32 ≦50 nm, and 0.6≦( d   31   ·n   31   +d   32   ·n   32 )/λ≦0.9 or 1.2≦( d   31   ·n   32   +d   32   ·n   32 )/λ≦1.5,  
       wherein λ represents a wavelength of a reproducing laser.  
     
     
         7 . The magneto-optical recording medium according to  claim 6 , in which said primary dielectric layer is composed of a material selected from the group of silicon nitride, germanium nitride, silicon nitride containing hydrogen at an amount of not more than 30 atom %, and germanium nitride containing hydrogen at an amount of not more than 30 atom %.  
     
     
         8 . The magneto-optical recording medium according to  claim 1 , in which said reflection layer is provided by the lamination of a primary reflection layer and a secondary reflection layer in this order, wherein the thermal conductivity of said secondary reflection layer is higher than that of said primary reflection layer.  
     
     
         9 . The magneto-optical recording medium according to  claim 1 , in which said reflection layer is provided by the lamination of a thermal diffusion layer, a thermal insulating layer, and a reflection layer in the above order.  
     
     
         10 . The magneto-optical recording medium according to  claim 1 , in which said reflection layer is composed of a metal film having the thermal conductivity of not less than 4×10 6  erg/(K·cm·s) and not more than 2×10 7  erg/(K·cm·s).  
     
     
         11 . The magneto-optical recording medium according to  claim 9 , in which said thermal diffusion layer is composed of a metal film having the thermal conductivity of not less than 4×10 6  erg/(K·cm·s) and not more than 2×10 7  erg/(K·cm·s).  
     
     
         12 . The magneto-optical recording medium according to  claim 1 , in which said reflection layer is composed of a metal film containing a noble metal or Cu at an amount of not less than 90 atom %.  
     
     
         13 . The magneto-optical recording medium according to  claim 9 , in which said thermal diffusion layer is composed of a metal film containing a noble metal or Cu at an amount of not less than 90 atom %.  
     
     
         14 . The magneto-optical recording medium according to  claim 12 , in which said reflection layer is composed of an alloy obtained by adding at least one element selected from the group of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W at n amount of from 0.1 to 10 atom % to Au.  
     
     
         15 . The magneto-optical recording medium according to  claim 13 , in which said thermal diffusion layer is composed of an alloy obtained by adding at least one element selected from the group of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W at an amount of from 0.1 to 10 atom % to Au.  
     
     
         16 . The magneto-optical recording medium according to  claim 12 , in which said reflection layer is composed of an alloy of Au and Cu.  
     
     
         17 . The magneto-optical recording medium according to  claim 13 , in which said thermal diffusion layer is composed of an alloy of Au and Cu.  
     
     
         18 . The magneto-optical recording medium according to  claim 12 , in which said reflection layer is composed of an alloy obtained by adding at least one element selected from the group of Au, Pt and Pd at an amount of from 0.1 to 10 atom % and at least one element selected from the group of Cu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W at an amount of from 0.1 to 10 atom % to Ag.  
     
     
         19 . The magneto-optical recording medium according to  claim 13 , in which said thermal diffusion layer is composed of an alloy obtained by adding at least one element selected from the group of Au, Pt and Pd at an amount of from 0.1 to 10 atom % and at least one element selected from the group of Cu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W at an amount of from 0.1 to 10 atom % to Ag.  
     
     
         20 . The magneto-optical recording medium according to  claim 1 , in which a thin film having a thickness of from 1 to 30 nm and composed of at least one element selected from the group of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W is provided as an underlayer between said substrate and said reflection layer.  
     
     
         21 . The magneto-optical recording medium according to  claim 9 , in which a thin film having a thickness of from 1 to 30 nm and composed of at least one element selected from the group of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W is provided as an underlayer between said substrate and said thermal diffusion layer.  
     
     
         22 - 31 . (canceled).