Perpendicular magnetic recording medium and magnetic recording and reproducing apparatus

1. A perpendicular magnetic recording medium comprising a nonmagnetic substrate, and at least a soft magnetic layer (SUL), an alignment control layer, a magnetic recording layer and a protective layer formed on the nonmagnetic substrate;

wherein the magnetic recording layer is constituted of two or more layers

and includes a first magnetic recording layer and a second magnetic recording layer from the nonmagnetic substrate side and,

regarding magnetocrystalline anisotropic energy Ku of each magnetic recording layer,

the first magnetic recording layer has 4×10 6 erg/cc or higher

and the second magnetic recording layer has 2×10 6 erg/cc or lower,

wherein the first magnetic recording layer is constituted of CoCrPtRu magnetic alloy crystal grains and grain boundaries made of an oxide, wherein the first magnetic recording layer contains 3 to 8 atomic % of at least one element selected from the group consisting of Al, V, Ti, Mo, Nb, Zr, W, Ta, Hf, Re, Gd, Tb, Sm, Ce, Nd and Pr in CoCrPtRu magnetic alloy crystal grains,

and the area of grain boundaries is 30% to 35% based on the entire area in a planar TEM observation of the first magnetic recording layer.

2. The perpendicular magnetic recording medium according to claim 1 , which includes an exchange coupling control layer between the first magnetic recording layer and the second magnetic recording layer.

3. The perpendicular magnetic recording medium according to claim 1 ,

wherein the first magnetic recording layer

also contains at least one element selected from the group consisting of Al, B, Bi, Ca, Cr, Fe, Hf, Mg, Mo, Nb, Ru, Si, Ta, Ti, W and Zr in grain boundaries.

4. A magnetic recording and reproducing apparatus comprising a magnetic recording medium, and a magnetic head for recording information on the magnetic recording medium and reproducing information from the magnetic recording medium, wherein the magnetic recording medium is the perpendicular magnetic recording medium according to claim 1 .

5. The perpendicular magnetic recording medium according to claim 1 , wherein the area of grain boundaries is 32% to 35% based on the entire area in a planar TEM observation of the first magnetic recording layer.

6. The perpendicular magnetic recording medium according to claim 5 , wherein the first magnetic recording layer has a magnetocrystalline anisotropic energy Ku of 4×10 6 erg/cc to 5.8×10 6 erg/cc.

7. The perpendicular magnetic recording medium according to claim 1 , wherein the area of grain boundaries is 32% to 34% based on the entire area in a planar TEM observation of the first magnetic recording layer.

8. The perpendicular magnetic recording medium according to claim 7 , wherein the first magnetic recording layer has a magnetocrystalline anisotropic energy Ku of 4×10 6 erg/cc to 5.8×10 6 erg/cc.

9. The perpendicular magnetic recording medium according to claim 1 , wherein the first magnetic recording layer has a magnetocrystalline anisotropic energy Ku of 4×10 6 erg/cc to 5.8×10 6 erg/cc.