Patent ID: 8652660

Claim:
A glass substrate for a magnetic recording medium, which is comprised of glass comprising K 2 O within a range of 0 to 1 mole percent and having: a glass transition temperature of equal to or greater than 600° C., an average coefficient of linear expansion at 100 to 300° C. of equal to or greater than 70×10-7/° C., a Young's modulus of equal to or greater than 81 GPa, a specific modulus of elasticity of equal to or greater than 30 MNm/kg, and a fracture toughness value of equal to or greater than 0.9 MPa m½, wherein the glass further comprises Li 2 O and Na 2 O and has a molar ratio {K 2 O/(Li 2 O+Na 2 O+K 2 O)} of the K 2 O content to the total content of the alkali metal oxides is equal to or lower than 0.13.