Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2002-05-23
2004-01-13
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S900000, C427S128000, C427S131000, C204S192200
Reexamination Certificate
active
06677061
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetic recording medium, to a process for producing the medium, and to a magnetic read/write apparatus including the medium.
BACKGROUND OF THE INVENTION
Most conventional magnetic recording media are of a longitudinal recording type, in which easy-magnetization axes in a magnetic film are mostly (more than 50%) oriented horizontally with respect to a substrate.
When recording density is increased in such a longitudinal magnetic recording medium, bit volume becomes excessively small, and read/write properties of the medium may deteriorate as a result of thermal instability. In addition, when recording density is increased, the effect of a diamagnetic field at a recording bit boundary causes an increase in medium noise.
In contrast, in a perpendicular magnetic recording medium, in which easy-magnetization axes in a magnetic film are mostly (more than 50%) oriented vertically with respect to a substrate, even when recording density is increased, the effect of a diamagnetic field at a recording bit boundary is minimal, and recording magnetic domains having clear boundaries are formed, thus enabling noise reduction. Furthermore, even when bit volume is relatively large, recording density can be increased, and thus thermal decay can be enhanced. Therefore, a perpendicular magnetic recording medium has recently become of interest.
In recent years, there has been a demand for magnetic recording media of higher recording density.
In order to increase recording density, a single-pole head exhibiting excellent ability to record data onto a perpendicular magnetic film is employed. Therefore, there has been proposed a magnetic recording medium including a film formed from a soft magnetic material (called a “backing layer”) provided between a substrate and a perpendicular magnetic film serving as a recording layer. Such a magnetic recording medium is advantageous in that the ratio of magnetic flux into the medium to magnetic flux from the single-pole head can be enhanced.
However, the aforementioned magnetic recording medium including a soft magnetic film (a backing layer) is not satisfactory in terms of read/write properties, and thus there has been a demand for a magnetic recording medium which exhibits excellent read/write properties.
Japanese Patent Application Laid-Open (kokai) No. 2-152208 discloses a magnetic recording medium including a soft magnetic film (a backing layer) formed from Co (50 to 75 at %)−M′ (wherein M′ is Ti, Zr, Hf, Nb, Ta, Mo, or W) (4 to 25 at %)−N (1 to 35 at %).
In general, saturation magnetization of a soft magnetic film formed from a Co alloy is lowered when the Co content is less than 85 at %. Therefore, the soft magnetic film must be thickened, resulting in high surface roughness.
Thus, in the case of the aforementioned magnetic recording medium, the flying height of a magnetic head (the distance between the top surface of the magnetic recording medium and the lower surface of the magnetic head) cannot be reduced sufficiently during read/write of data, resulting in difficulty in attaining high recording density. In addition, formation of a thick soft magnetic film results in lowered productivity.
Japanese Patent Application Laid-Open (kokai) No. 11-149628 discloses a magnetic recording medium including a soft magnetic undercoat film formed from an FeAlSi alloy or an FeTaN alloy, which medium prevents generation of sporadic spike noise and improves envelope properties.
Although the aforementioned magnetic recording medium exhibits improved envelope properties, the medium generates increased medium noise attributed to the soft magnetic undercoat film. This is because, micronized crystal grains of the soft magnetic undercoat film increase magnetic bonding between the crystal grains, resulting in an increase in magnetic cluster size (i.e., size of magnetically bonded grains).
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a magnetic recording medium which enables reduction of medium noise generated from a soft magnetic undercoat film, to thereby improve read/write properties and to attain high read/write density; a process for producing the medium; and a magnetic read/write apparatus including the medium.
In order to attain the aforementioned object, the present invention provides the following.
The magnetic recording medium of the present invention comprises a non-magnetic substrate; a soft magnetic undercoat film containing at least a soft magnetic material; an orientation-regulating film for regulating the crystal orientation of a film provided directly thereon; a perpendicular magnetic film in which easy-magnetization axes are mostly oriented vertically with respect to the substrate; and a protective film, the films being formed on the substrate, wherein the soft magnetic undercoat film contains a material represented by the following composition:
aFe-bCo-cM-dX1b-fN
wherein M is one or more elements selected from the group consisting of Ti, Zr, Nb, Hf, Ta, V, and Mo; X1 is one or more elements selected from the group consisting of Cr, Ga, Al, Si, and Ni; and a, b, c, d, and f represent atomic percentages and satisfy the following relations: 60≦a+b≦90, 30≦a≦90, 5≦c≦20, 0.1≦d≦7, and 3≦f≦30.
The soft magnetic undercoat film may contain a material represented by the following composition:
aFe-bCo-cM-eX2-fN
wherein M is one or more elements selected from the group consisting of Ti, Zr, Nb, Hf, Ta, V, and Mo; X2 is one or more elements selected from the group consisting of P, C, B, and O; and a, b, c, e, and f represent atomic percentages and satisfy the following relations: 60≦a+b≦90, 30≦a≦90, 5≦c≦20, 0.1≦e≦10, and 3≦f≦30.
The soft magnetic undercoat film may contain a material represented by the following composition:
aFe-bCo-cM-dX1-eX2-fN
wherein M is one or more elements selected from the group consisting of Ti, Zr, Nb, Hf, Ta, V, and Mo; X1 is one or more elements selected from the group consisting of Cr, Ga, Al, Si, and Ni; X2 is one or more elements selected from the group consisting of P, C, B, and O; and a, b, c, d, e, and f represent atomic percentages and satisfy the following relations: 60≦a+b ≦90, 30≦a≦90, 5≦c≦20, 0.1≦d≦7,0.1≦e≦7, and 3≦f≦30.
Preferably, the aforementioned a through f satisfy the following relations: 60≦a+b≦80, 30≦a≦80, 5≦c≦20, 0.1≦d≦3, 0.1≦e≦5, and 8≦f≦25.
Preferably, the soft magnetic undercoat film comprises fine crystals containing Fe as a primary component and having an average grain size of 13 nm or less, and an amorphous phase containing M (M is one or more elements selected from the group consisting of Ti, Zr, Nb, Hf, Ta, V, and Mo) and N in amounts greater than those contained in the fine crystals.
Preferably, the fine crystals have a bcc structure.
Preferably, the soft magnetic undercoat film has a saturated magnetic flux density (Bs) of at least 1 T. More preferably, the soft magnetic undercoat film has a saturated magnetic flux density of at least 1.4 T.
The product of the saturated magnetic flux density (Bs) and thickness (t) of the soft magnetic undercoat film; i.e., Bs·t, is preferably at least 50 T·nm, more preferably at least 100 T·nm.
The orientation-regulating film may comprise an hcp-structure material containing one or more elements selected from the group consisting of Ti, Zn, Y, Zr, Ru, Re, Gd, Tb, and Hf in a total amount of at least 50at %.
The orientation-regulating film may comprise an fcc-structure material containing one or more elements selected from the group consisting of Ni, Cu, Pd, Ag, Pt, Ir, Au, and Al in a total amount of at least 50at %.
Preferably, a portion or the entirety of a surface of the soft magnetic undercoat film facing the perpendicular magnetic film is oxidized.
Preferably, the perpendicular magnetic film has a nucleation field (−Hn) of at least 0 (Oe).
The process of the present invention for p
Sakai Hiroshi
Sakawaki Akira
Shimizu Kenji
Rickman Holly
Showa Denko Kabushiki Kaisha
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