Magnetic recording medium and magnetic recording and reproducing apparatus

1. A magnetic recording medium comprising:

a substrate;

an under-layer formed on the substrate;

a magnetic layer formed on the under-layer; and

a protective layer formed on the magnetic layer;

wherein the magnetic layer comprises Cc, Cr and Pt;

a thickness of the magnetic layer is from 10 nm to 22 nm;

a coercivity of the magnetic layer is not less than 2000 Oe; and

a fluctuation field of magnetic viscosity at 25° C. and at a field strength equal to remanence coercivity or coercivity is greater than 30 Oe.

2. A magnetic recording medium according to claim 1 , wherein the protective layer comprises at least one material as a single or composite material selected from the group consisting of a carbon film, an oxide film, a plasma polymerized film, a fatty acid, a perfluorocarbon carboxylic acid, and a perfluoropolyether.

3. A magnetic disk unit comprising;

a magnetic head having a reproducing head and a recording head;

a magnetic recording medium comprising a substrate, an under-layer formed on the substrate, a magnetic layer formed on the under-layer and a protective layer formed on the magnetic layer; and

a signal processor system;

wherein said magnetic layer comprises Co, Cr and Pt;

a thickness of the magnetic layer is from 10 nm to 22 nm;

a coercivity of the magnetic layer is not less than 2000 Oe; and

a fluctuation field of magnetic viscosity at 25 ° C. and at a field strength equal to remanence coercivity or coercivity greater than 30 Oe.

4. A magnetic disk unit according to claim 3 , wherein the magnetic recording medium has a recording density of not less than 2 gigabit/square inch.

5. A magnetic disk unit according to claim 3 . wherein the protective layer comprises at least one material as a single or composite material selected from the group consisting of a carbon film, an oxide film, a plasma polymerized film, a fatty acid, a perfluorocarbon carboxylic acid, and a perfluoropolyether.