Perpendicular magnetic recording medium and process for manufacture thereof

A perpendicular magnetic recording medium, comprising in the following order:

• a base;
• a first magnetic recording layer having a granular structure in which a non-magnetic grain boundary portion is formed between magnetic particles grown continuously in a columnar shape;
• a second magnetic recording layer having a granular structure in which a non-magnetic grain boundary portion is formed between magnetic particles grown continuously in a columnar shape;
• a non-magnetic split layer;
• and
• an auxiliary recording layer magnetically approximately continuous in an in-plane direction of a main surface of the base, wherein
• the first magnetic recording layer and the second magnetic recording layer are Co alloys containing Pt, and the Pt content of the second magnetic recording layer is lower than that of the first magnetic recording layer.

A perpendicular magnetic recording medium, comprising in the following order:

• a base;
• a first magnetic recording layer having a granular structure in which a non-magnetic grain boundary portion is formed between crystal particles grown in a columnar shape;
• a second magnetic recording layer having a granular structure in which a non-magnetic grain boundary portion is formed between crystal particles grown in a columnar shape;
• a second split layer that is disposed on the second magnetic recording layer and that contains a Ru alloy as a main component and;
• a third magnetic recording layer having a granular structure in which a non-magnetic grain boundary portion is formed between crystal particles grown in a columnar shape;
• a split layer that is disposed on the third magnetic recording layer and that contains a Ru alloy as a main component;
• and
• an auxiliary recording layer that is disposed on the split layer and that is magnetically approximately continuous in an in-plane direction of a main surface of the base.

A perpendicular magnetic recording medium, comprising:

• a base;
• a magnetic recording layer having a granular structure in which a non-magnetic grain boundary portion is formed between crystal particles grown in a columnar shape;
• a non-magnetic split layer provided as an upper layer of the magnetic recording layer;
• an auxiliary recording layer that is provided as an upper layer of the split layer and that is magnetically approximately continuous in an in-plane direction of a main surface of the base;
• a protective layer that is provided as an upper layer of the auxiliary recording layer and that contains carbon as a main component;
• and
• a lubricating layer disposed on the protective layer, wherein,
• when the protective layer is excited by an argon ion laser with a wavelength of 514.5 nm to measure a Raman spectrum, fluorescent background in the range of wave number of 900 cm−1 to 1800 cm−1 of the Raman spectrum is corrected by linear approximation, and a D peak that appears at around 1350 cm−1 and a G peak that appears at around 1520 cm−1 are subjected to waveform separation by Gaussian function, the ratio of D peak height (Dh) to G peak height (Gh) is in a range from 0.70 to 0.95.

A method of manufacturing a perpendicular magnetic recording medium, comprising:

• forming, on a substrate, a magnetic recording layer having a granular structure in which a non-magnetic grain boundary portion is formed between crystal particles grown in a columnar shape;
• forming a non-magnetic split layer at an upper layer of the magnetic recording layer;
• forming an auxiliary recording layer magnetically approximately continuous in an in-plane direction of a main surface of the base, as an upper layer of the split layer;
• heating the perpendicular magnetic recording medium such that, when a protective layer, which is formed later, is excited by an argon ion laser with a wavelength of 514.5 nm to measure a Raman spectrum, fluorescent background in the range of wave number of 900 cm−1 to 1800 cm−1 of the Raman spectrum is corrected by linear approximation, and a D peak that appears at around 1350 cm−1 and a G peak that appears at around 1520 cm−1 are subjected to waveform separation by Gaussian function, the ratio of D peak height (Dh) to G peak height (Gh) is in a range from 0.70 to 0.95;
• and
• forming the protective layer by CVD.