Perpendicular magnetic recording medium with grain boundary controlling layers

A perpendicular magnetic recording medium, comprising:

• an oxide recording layer comprising an oxide;
• a non-oxide recording layer which does not contain an oxide positioned above the oxide recording layer;
• wherein the oxide recording layer comprises:
• a first recording layer;
• a second recording layer;
• a third recording layer;
• and
• a fourth recording layer,
• wherein an oxide concentration of the first recording layer is greater than an oxide concentration of the second recording layer,
• wherein an oxide concentration of the third recording layer is greater than an oxide concentration of the fourth recording layer, and
• wherein the oxide concentration of the third recording layer is greater than the oxide concentration of the second recording layer.

A method, comprising:

• forming a first oxide recording layer comprising an oxide above a substrate;
• forming a second oxide recording layer on the first oxide recording layer;
• forming a third oxide recording layer on the second oxide recording layer;
• forming a fourth oxide recording layer on the third oxide recording layer;
• and
• forming a non-oxide recording layer which does not contain an oxide on the fourth oxide recording layer,
• wherein an oxide concentration of the first oxide recording layer is greater than an oxide concentration of the second oxide recording layer,
• wherein an oxide concentration of the third oxide recording layer is greater than an oxide concentration of the fourth oxide recording layer, and
• wherein the oxide concentration of the third oxide recording layer is greater than the oxide concentration of the second oxide recording layer.