The present invention relates to a magnetic recording medium and a magnetic recording apparatus. In particular, the present invention relates to a perpendicular magnetic recording medium suitable for a high recording density and a magnetic recording apparatus having a perpendicular magnetic recording medium.
Attention has been paid to perpendicular recording as a technology for achieving a high recording density in a magnetic recording in lieu of a longitudinal magnetic recording of the prior art. In a perpendicular recording, a combination of a double layer perpendicular magnetic recording medium, which is composed of a soft magnetic underlayer and a perpendicular recording layer, and a single-pole type head is effective to realize a high recording density. In general, because a soft magnetic underlayer is composed of a soft magnetic material with high saturation flux density (Bs), it has been pointed out that problems arise such as leakage magnetic flux generated by domain walls of the soft magnetic underlayer being observed as spike noise and the recorded magnetization being erased by moving the domain walls. Moreover, the thickness of the soft magnetic underlayer is as thick as from several tens of nanometers to several hundreds of nanometers, so that there is a possibility that the surface smoothness is deteriorated, the formation of the perpendicular recording layer and the fly stability of the head influenced harmfully, and the adhesion to the substrate deteriorated because of a large film stress.
As a means to solve these problems, a method is proposed in which the wall motion of the soft magnetic underlayer is prevented by an exchange coupling with an antiferromagnetic layer where the magnetic spin is aligned in the same direction as that disclosed in Patent Document 1 (JP-A No. 103553/1994). Furthermore, in Patent Document 2 (JP-A No.155321/2001), a method is disclosed in which the soft magnetic underlayer is composed of two or more layers of soft magnetic layers being separated from each other by a nonmagnetic layer, and where the magnetization of the soft magnetic layer is fixed toward the opposite direction. However, these methods are effective to prevent the soft magnetic underlayer from wall motion, but the problems such as surface smoothness of the soft magnetic underlayer and the fly stability of the head cannot be solved.
Patent Document 3 (JP-A No. 162806/2003) discloses a method in which a pre-coat layer to increase adhesion with a substrate and an fcc-structured nonmagnetic layer to improve the orientation of the antiferromagnetic layer are formed between the substrate and the anti-ferromagnetic layer. However, the method described above is also effective to prevent the soft magnetic underlayer from wall motion, but it does not describe the effect of the adhesion, so that the problem of the fly stability of the head cannot be solved at the same time.