Magnetic recording medium and its manufacturing process

A magnetic recording medium comprising:

• a glass substrate disk;
• an under layer formed on at least one surface of the glass substrate disk, said under layer comprising a layer of a spinel crystal structured magnetic iron oxide layer laminated on a layer of a sodium chloride crystal structured oxide layer, said spinel crystal structured magnetic iron oxide having a spinel crystal structure as determined by X-ray diffraction and comprising an iron oxide containing at least one element selected from the group consisting of zinc, manganese and nickel, and said sodium chloride crystal structured oxide having a sodium chloride crystal structure with crystal orientation in a <100>
• direction perpendicular to the surface of the glass substrate as determined by X-ray diffraction and containing at least one oxide selected from the group consisting of NiO, CoO and MnO;
• a layer of a ferromagnetic Co-containing iron oxide formed on a surface of the under layer in the form of columnar grains which are densely arranged perpendicularly to the surface of the under layer, said ferromagnetic Co-containing iron oxide having a spinel crystal structure with crystal orientation in a <100>
• direction perpendicular to the surface of the under layer as determined by X-ray diffraction;
• and
• a lubricant layer formed on the layer of the ferromagnetic Co-containing iron oxide;
• wherein the under layer is different from the layer of the ferromagnetic Co-containing iron oxide.