The present invention relates to a magnetic recording medium employed in an apparatus such as a magnetic disk apparatus; a process for producing the magnetic recording medium; a magnetic recording and reproducing apparatus comprising the magnetic recording medium; and a method for evaluating a profile in relation to inclination of crystal planes on a magnetic film surface.
A conventional, widely employed magnetic recording medium is of a longitudinal recording type in which most of the easy-magnetization axes in the magnetic film are oriented horizontally with respect to the substrate. The term magnetic anisotropy is used to describe the dependence of internal energy on the direction of spontaneous magnetization, and the stable direction of spontaneous magnetization is called xe2x80x9ceasy-magnetization axisxe2x80x9d. In the case of longitudinal type, the term xe2x80x9cmostxe2x80x9d used herein describes the state of longitudinal orientation when the coercive force in the in-plane direction is higher than the coercive force of the vertical direction when the coercive force of the magnetic recording medium is measured.
In such a longitudinal magnetic recording medium, when recording density is increased, per-bit volume becomes exceedingly small and reproduction characteristics may deteriorate due to thermal instability. In addition, when recording density is increased, the effect of a diamagnetic field at a recording bit boundary may cause an increase in medium noise.
In contrast, in a perpendicular magnetic recording medium in which most of the easy-magnetization axes in the magnetic film are oriented vertically with respect to the substrate, the effect of a diamagnetic field at a recording bit boundary is minimal even when recording density is increased, and recording magnetic domains having clear boundaries are formed. In the case of perpendicular type, the term xe2x80x9cmostxe2x80x9d used herein describes the state of vertical orientation when the coercive force in the vertical direction is higher than the coercive force of the in-plane direction when the coercive force of the magnetic recording medium is measured. As a result, noise can be reduced. In addition, even when bit volume is relatively large, recording density can be increased, and thus resistance to thermal decay is high. Therefore, a perpendicular magnetic recording medium has recently become of interest, and magnetic recording medium structures suitable for perpendicular magnetic recording have been proposed.
In recent years, there has been a demand for magnetic recording media of higher recording density, and in accordance with this trend, further improvements to noise characteristics have been required.
In view of the foregoing, an object of the present invention is to provide a magnetic recording medium exhibiting excellent noise characteristics, and a process for producing the magnetic recording medium effectively.
The present inventors have found that when a rocking curve in relation to a perpendicular magnetic film has a plurality of local maximum points, noise characteristics can be enhanced. The present invention has been accomplished on the basis of this finding.
In order to solve the aforementioned problems, the present invention provides a magnetic recording medium comprising a substrate; an undercoat film formed thereon; and a perpendicular magnetic film in which most of the easy-magnetization axes are oriented vertically with respect to the substrate, the magnetic film being formed on the undercoat film, wherein a rocking curve in relation to the magnetic film has a plurality of local maximum points, the curve being obtained through xcex8-2xcex8 scanning employing X-ray diffraction.
When the magnetic recording medium is subjected to magnetization, the magnetization direction is not a specific direction and varies to some extent, since there are a plurality of local maximum points in the orientation direction of crystals in the perpendicular magnetic film.
Therefore, at the boundary between two adjacent recording magnetic domains, the magnetization direction of one magnetic domain is not completely opposite that of the other magnetic domain, but slightly deviates from the opposite direction. Thus, compared with when the magnetization directions are completely opposite to each other, magnetic fluctuations, which would otherwise stem from magnetic interaction between the magnetic domains, may be absent in the vicinity of the magnetic domain wall.
As a result, generation of noise attributed to magnetic fluctuations can be prevented, and noise characteristics can be enhanced.
In order to enhance noise characteristics, the difference between an incident angle of an incident X-ray beam the incident X-ray beam being employed when the rocking curve is obtained corresponding to either of the local maximum points and an incident angle corresponding to the peak of a diffracted X-ray beam of a dominant crystal plane in the surface of perpendicular magnetic film, is preferably 3-10xc2x0 in the rocking curve.
The half width of a peak portion of the rocking curve is preferably 10-30xc2x0.
Preferably, the perpendicular magnetic film comprises any alloy selected from among a Co/Cr alloy, a Co/Cr/Pt alloy, a Co/Cr/Ta alloy, and a Co/Cr/Pt/X (X: one or more species of Ta, Zr, Cu, Re, Nb, Si, Ge, and B) alloy.
The present invention also provides a process for producing a magnetic recording medium, which comprises forming an undercoat film on a substrate, and forming, on the undercoat film, a perpendicular magnetic film in which most of the easy-magnetization axes are oriented vertically with respect to the substrate, so that a rocking curve obtained through xcex8-2xcex8 scanning employing X-ray diffraction has a plurality of local maximum points.
The present invention also provides a magnetic recording and reproducing apparatus comprising the aforementioned magnetic recording medium, and a magnetic head for recording data onto the medium and reproducing the data therefrom.
The present invention also provides a method for evaluating a profile in relation to inclination of crystal planes in a magnetic film surface, which method comprises: (1) a peak determination step for determining the peak intensity of a diffracted X-ray beam through xcex8-2xcex8 scanning; (2) a step for determining a rocking curve; and (3) a step for determining the number of local maximum points in the resultant rocking curve. In the peak determination step, when a disk including a perpendicular magnetic film on the outermost surface of the disk is irradiated with an incident X-ray beam and the diffracted X-ray beam is detected by a diffracted-X-ray detector, the position of the detector is determined such that the angle of the diffracted X-ray beam with respect to the incident X-ray beam is twice the incident angle of the incident X-ray beam with respect to a disk plane, the incident angle of the incident X-ray beam is varied by varying the direction of the disk during irradiation of the incident X-ray beam, while, simultaneously, varying the position of the detector so that the angle of the diffracted X-ray beam with respect to the incident X-ray beam is maintained to be twice the incident angle of the incident X-ray beam. The intensity of the diffracted X-ray beam is measured by the detector through xcex8-2xcex8 scanning to determine the position of the detector so that the intensity of the diffracted X-ray beam reaches its maximum. Further, in the rocking curve determination step, the detector is fixed at the position determined in the peak determination step, and then the incident angle of the incident X-ray beam is varied by varying the direction of the disk to determine a rocking curve showing the relation between the incident angle and the intensity of the diffracted X-ray beam detected by the detector. In the step for determining the number of local maximum points, the number of local maximum points is counted on the basis of the shape of the rocking curve; and a profile in relation to inclination of crystal planes in the perpendicular magnetic film surface with respect to the disk plane is evaluated on the basis of the shape of the rocking curve and the number of the local maximum points, which are obtained through steps (1) through (3).
When the rocking curve does not seem to have a plurality of local maximum points because of overlapping of local maximum portions of the curve, a profile in relation to inclination of crystal planes in the perpendicular magnetic film surface with respect to the disk plane may be evaluated through the following steps. After steps (1) to (3), the rocking curve is separated into two separation curves through (A), an initial peak value determination step for providing an initial peak value of a separation curve; (B), an initial half-width determination step for providing an initial half-width of a separation curve; and (C), a separation curve preparation step for preparing a separation curve through operation processing by use of the determined initial peak value and initial half-width. In the initial peak value determination step, an initial peak value of each separation curve is determined on the assumption that the difference between an incident angle corresponding to the peak of a first separation curve and an incident angle corresponding to the peak of the diffracted X-ray beam of a dominant crystal plane in the perpendicular magnetic film surface is equal to that between an incident angle corresponding to the peak of a second separation curve and the incident angle corresponding to the peak of the diffracted X-ray beam of the dominant crystal plane in the perpendicular magnetic film surface. In the initial half-width determination step, an initial half-width is determined from twice the difference between the incident angle corresponding to the peak of either separation curve and the incident angle corresponding to the position representing xc2xd of the intensity of an X-ray beam of the rocking curve at the initial peak value. A profile in relation to inclination of crystal planes in the perpendicular magnetic film surface with respect to the disk plane is evaluated on the basis of the shape of the separation curve obtained through steps (A) through (C).