초록 ▼

An aspect of the present invention relates to glass for a magnetic recording medium substrate, which includes essential components in the form of SiO2, Li2O, Na2O, and one or more alkaline earth metal oxides selected from the group consisting of MgO, CaO, SrO, and BaO, wherein a molar ratio of a con

An aspect of the present invention relates to glass for a magnetic recording medium substrate, which includes essential components in the form of SiO2, Li2O, Na2O, and one or more alkaline earth metal oxides selected from the group consisting of MgO, CaO, SrO, and BaO, wherein a molar ratio of a content of MgO to a combined content of MgO, CaO, SrO, and BaO (MgO/(MgO+CaO+SrO+BaO)) is equal to or greater than 0.80, and which has a Young's modulus of equal to or greater than 80 GPa, and a glass transition temperature of equal to or greater than 620° C.

대표청구항 ▼

1. Glass for a magnetic recording medium substrate, which comprises: essential components in the form of SiO2, Li2O, Na2O, and one or more alkaline earth metal oxides selected from the group consisting of MgO, CaO, SrO, and BaO;wherein a molar ratio of a content of MgO to a combined content of MgO,

1. Glass for a magnetic recording medium substrate, which comprises: essential components in the form of SiO2, Li2O, Na2O, and one or more alkaline earth metal oxides selected from the group consisting of MgO, CaO, SrO, and BaO;wherein a molar ratio of a content of MgO to a combined content of MgO, CaO, SrO, and BaO (MgO/(MgO+CaO+SrO+BaO)) is equal to or greater than 0.80; andwhich has a glass transition temperature of equal to or greater than 620° C., andwherein a specific modulus of elasticity is equal to or greater than 30 MNm/kg. 2. Glass for a magnetic recording medium substrate, which comprises: essential components in the form of SiO2, Li2O, Na2O, and one or more alkaline earth metal oxides selected from the group consisting of MgO, CaO, SrO, and BaO;wherein a molar ratio of a content of CaO to a combined content of MgO, CaO, SrO, and BaO (CaO/(MgO+CaO+SrO+BaO)) is equal to or less than 0.20; and which has a glass transition temperature of equal to or greater than 620° C., andwherein a specific modulus of elasticity is equal to or greater than 30 MNm/kg. 3. The glass for a magnetic recording medium substrate according to claim 1, which has a Young's modulus of equal to or greater than 80 GPa. 4. The glass for a magnetic recording medium substrate according to claim 2, which has a Young's modulus of equal to or greater than 80 GPa. 5. A magnetic recording medium substrate blank, which is comprised of the glass for a magnetic recording medium substrate according to claim 1. 6. A magnetic recording medium substrate blank, which is comprised of the glass for a magnetic recording medium substrate according to claim 2. 7. A magnetic recording medium substrate, which is comprised of the glass for a magnetic recording medium substrate according to claim 1. 8. A magnetic recording medium substrate, which is comprised of the glass for a magnetic recording medium substrate according to claim 2. 9. A magnetic recording medium substrate, which is comprised of chemically strengthened glass that has been prepared by chemically strengthening the glass for a magnetic recording medium substrate according to claim 1. 10. A magnetic recording medium substrate, which is comprised of chemically strengthened glass that has been prepared by chemically strengthening the glass for a magnetic recording medium substrate according to claim 2. 11. The magnetic recording medium substrate according to claim 1, which is comprised of glass having a fracture toughness value of equal to or greater than 0.9 MPa·m1/2. 12. The magnetic recording medium substrate according to claim 2, which is comprised of glass having a fracture toughness value of equal to or greater than 0.9 MPa·m1/2. 13. The magnetic recording medium substrate according to claim 9, which is comprised of chemically strengthened glass in which a tensile stress distribution is convex in shape such that the convex shape does not contain indentations indenting to a compressive stress side in a stress profile in a virtual cross section perpendicular to two main surfaces as obtained by the Babinet method. 14. The magnetic recording medium substrate according to claim 10, which is comprised of chemically strengthened glass in which a tensile stress distribution is convex in shape such that the convex shape does not contain indentations indenting to a compressive stress side in a stress profile in a virtual cross section perpendicular to two main surfaces as obtained by the Babinet method. 15. The magnetic recording medium substrate according to claim 9, which is comprised of chemically strengthened glass in which an average value Tav of a tensile stress obtained by the Babinet method and a maximum value Tmax of the tensile stress satisfy the following expression (1): Tav/Tmax≧0.5. 16. The magnetic recording medium substrate according to claim 10, which is comprised of chemically strengthened glass in which an average value Tav of a tensile stress obtained by the Babinet method and a maximum value Tmax of the tensile stress satisfy the following expression (1): Tav/Tmax≧0.5. 17. A magnetic recording medium, which comprises a magnetic recording layer on the magnetic recording medium substrate according to claim 7. 18. A magnetic recording medium, which comprises a magnetic recording layer on the magnetic recording medium substrate according to claim 8. 19. A magnetic recording apparatus of energy-assisted magnetic recording system, which comprises: a heat-assisted magnetic recording head having a heat source to heat at least a main surface of a magnetic recording medium, a recording element member, anda reproduction element member; andthe magnetic recording medium according to claim 17. 20. A magnetic recording apparatus of energy-assisted magnetic recording system, which comprises: a heat-assisted magnetic recording head having a heat source to heat at least a main surface of a magnetic recording medium, a recording element member, anda reproduction element member; andthe magnetic recording medium according to claim 18.