JP4508183B2 - Dot-coupled pattern magnetic recording medium - Google Patents

Description

  The present invention relates to a patterned magnetic recording medium having a magnetic film in which recording bits are patterned. Such a bit pattern magnetic recording medium relates to a magnetic recording device mounted on various recording devices such as a computer and a video recorder.

As a technique for increasing the recording density of a magnetic recording apparatus, a perpendicular magnetic recording method has attracted attention. In this method, a magnetic thin film having a fine particle structure with magnetic anisotropy in the vertical direction is used as a recording medium, and information is recorded as a minute magnetization pattern by a magnetic head.
In the perpendicular magnetic recording method, adjacent magnetizations are coupled antiparallel with the magnetization transition as a boundary, so it becomes possible to maintain a more stable recording state against thermal magnetic relaxation compared to the in-plane magnetic recording method. Suitable for high density.

However, even in the perpendicular magnetic recording system, as in the case of the in-plane magnetic recording system, it is necessary to reduce the size of the fine particles of the recording medium to about 1/10 as the recording bit length decreases. As the bit length decreases, the magnetic energy held by the magnetic particles decreases and the effect of thermal magnetic relaxation appears.
Increasing the magnetic anisotropy of the magnetic material is effective for increasing the magnetic energy of the magnetic particles. However, the magnetic field strength required for magnetization reversal during recording also increases, and recording with a magnetic head is difficult. There was a problem that it could not be done.

As a method of breaking through the limit due to the thermomagnetic relaxation phenomenon of this magnetic recording medium, a bit pattern magnetic recording medium in which the area of a magnetic dot is the size of a bit has been proposed (see Non-Patent Document 1 and Non-Patent Document 2). .
Bit pattern magnetic recording media can increase the magnetic particle volume by increasing the size of the magnetic dots, thereby increasing the magnetic energy and increasing the magnetic energy without increasing the magnetic anisotropy. Can be secured.
Regarding bit pattern magnetic recording media, there has already been proposed a recording medium with thermomagnetic stability aimed at an areal recording density of 1 Tbit / in ² (Naoki Honda, “1 Tbit / in ² patterned media for recording”). Design, "IEICE Technical Report, vol. 105, no. 115, pp. 51-56, 2005).
However, in order to realize higher density recording, for example, 2 Tbit / in ² , it is necessary to arrange bit patterns at twice the density. In this case, simply reducing the distance between the magnetic dots increases the magnetostatic interaction between the dots, resulting in a decrease in the magnetization reversal start magnetic field and an increase in the saturation magnetic field of the magnetic dot array.
For this reason, in order to ensure the thermomagnetic stability, it is necessary to provide a larger magnetic anisotropy to compensate for the decrease in the magnetization reversal starting magnetic field. However, if this is done, the saturation magnetic field increased by the magnetostatic interaction will further increase, and the magnetic field strength required for recording will become extremely large. For this reason, a recording magnetic field that cannot be realized by a magnetic head is required.
In addition, since the difference between the magnetization reversal start magnetic field and the saturation magnetic field becomes large, even if the magnetization reversal is possible, the allowable deviation in the track longitudinal direction of the head magnetic field for obtaining the intended recording becomes extremely small compared to the reduction of the bit length. End up.
On the other hand, in order to keep the distance between the magnetic dots large, it is conceivable to reduce the size of the magnetic dots, but this also increases the magnetic anisotropy and increases the magnetic energy by the amount of the dot volume. It is necessary to ensure stability. For this reason, even if the magnetic dot size is reduced, it is not a solution to the problem that recording is impossible.

Robert L. White, Richard M. et al. H. New, and R.C. Fabian W. Pease, “Patterned Media: A Viable Route to 50 Gbit / in2 and up for Magnetic Recording ?,” IEEE Trans. Magn. , Vol. 33, no. 1, pp. 990-995, Jan. 1997.

Gordon F. Hughes, “Patterned Media Write Designs,” IEEE Trans. Magn. , Vol. 36, no. 2, pp. 521-526, March 2000.

As described above, when the bit pattern magnetic recording medium achieves a surface recording density of 1 Tbit / in ² or more, an increase in magnetostatic interaction between the magnetic dots is suppressed without reducing the magnetic dot size. The introduction of means is essential.

An object of the present invention is to provide a bit pattern magnetic recording medium capable of effectively suppressing an increase in magnetostatic interaction between magnetic dots even when arranged at a high density in order to realize a recording density of 1 Tbit / in ² or more. There is to do.

The present invention of claim 1 is a patterned magnetic recording medium comprising magnetic dots comprising a magnetic film having a magnetic anisotropy in a vertical direction and patterned in a dot shape , wherein a part of the magnetic dots is in the track longitudinal direction. The coupling section cross-sectional area between the magnetic dots is 30% or less of the maximum cross-sectional area in the track width direction of the magnetic dots, and the surface recording density is ² Tbit / in ² or more. This is a patterned magnetic recording medium.
Furthermore, the present invention of claim 2 is characterized in that the cross-sectional area of the coupling portion between the magnetic dots is 10 to 25% of the maximum cross-sectional area of the magnetic dots in the track width direction. It is a magnetic recording medium.

According to the present invention, in a bit pattern magnetic recording medium having a magnetic anisotropy in the vertical direction and including a magnetic film patterned in a dot shape, the dots are partially coupled in the track longitudinal direction of the dot end. Thus, a method for effectively suppressing the magnetostatic interaction between dots is provided, and a magnetic information recording apparatus having a recording density of 1 Tbit / in ² or more can be realized with a sufficient head deviation tolerance.

  In the dot-coupled pattern magnetic recording medium of the present invention, the cross-sectional area of the dot coupling portion needs to be 30% or less of the maximum cross-sectional area of the dot in the track width direction in order to avoid deterioration of recording characteristics due to the influence of exchange coupling. Yes, a great effect is obtained at 10-25%.

Hereinafter, the present invention will be described in more detail.
In the coupled bit pattern magnetic recording medium according to the present invention, magnetic dots having perpendicular magnetic anisotropy are arranged at high density on a soft magnetic backing layer provided with a nonmagnetic intermediate layer, and between the magnetic dots. Part of the longitudinal ends of the recording tracks of the dots are coupled so that exchange coupling works.
This combined cross-sectional area is set to 30% or less with respect to the cross-sectional area of the dot in the track width direction. Desirably, it is set between 10-25%.
In the bit pattern medium, the magnetostatic interaction acting between the dots increases as the distance between the dots decreases. For this reason, the magnetization reversal start magnetic field of the magnetic dots decreases and the saturation magnetic field increases, and not only a large recording magnetic field is required, but also the magnetization reversal magnetic field width, which is the difference between them, increases, and the switching timing of the recording magnetic field The allowable width for the shift in the longitudinal direction becomes extremely small compared to the decrease in the dot interval.
However, by providing the coupling between the dots, the magnetostatic interaction acting between the dots is effectively suppressed by the exchange coupling, and the magnetization reversal magnetic field width of the magnetic dots is narrowed. For this reason, in addition to reducing the required recording magnetic field strength, it is possible to have a larger allowable width with respect to the deviation in the longitudinal direction of the switching timing of the recording magnetic field.
Further, since anisotropy in the track longitudinal direction is imparted, even if the recording magnetic field is shifted in the track width direction, recording on the adjacent track is suppressed, and a larger displacement tolerance is obtained.
For this reason, if the present invention is applied, a sufficient shift margin in the track longitudinal and width directions is secured for a patterned medium having a high density of 1 Tbit / in ² or more, and a high density magnetic recording system is realized. It becomes possible to do.

The result of confirming that the magnetization reversal magnetic field width is reduced by coupling between magnetic dots will be described.
By DC magnetron sputtering deposition, a Co-Zr-Nb alloy soft magnetic film with a thickness of 50 nm is formed on a glass substrate, a carbon film is formed thereon with a thickness of 5 nm, and further Pt is formed with a thickness of 10 nm. A Co ₈₀ Pt ₂₀ alloy film having a thickness of 20 nm was formed. A 1 μm square region of this Co ₈₀ Pt ₂₀ alloy layer was set to a dot size of 70 nm square and an inter-dot spacing of 20 nm using a FIB (focused ion beam) processing apparatus, thereby producing 10 × 10 dots. At this time, the sample A was manufactured by controlling the etching depth so that the magnetic material height between the dots remained 25%. For comparison, a comparative sample B from which all the magnetic material between dots was removed was also produced.
First, a magnetic field of 15 kOe is applied to these samples in the vertical direction to saturate the magnetization, and then the magnetic field is applied in the opposite direction, and the number of magnetic reversal dots N _rev in the residual state is set to MFM (magnetic force). The ratio [1-2 (N _tot −N _rev ) / N _tot ] with the total number of dots N _tot was _defined as the normalized residual magnetization. Furthermore, the strength of the reverse magnetic field was increased in 1 kOe step, and the number of inverted dots with respect to the applied magnetic field strength was examined.
As shown in FIG. 1, the normalized remanent magnetization curve with respect to the applied magnetic field strength of sample A has a larger slope in the vicinity of zero magnetization than that of comparative sample B. That is, it is shown that the reversal magnetic field width is small in the sample A in which a part between the dots is combined.
In the case of sample B with sufficient separation between the magnetic dots, the spacing between the dots is as small as 20 nm, so it can be interpreted that the slope of the magnetization curve is reduced by the magnetostatic interaction between the dots (Yuji Kondo, Toshiaki Keitoku, Shingo Takahashi, Naoki Honda, Kazuhiro Ouchi, “Magnetic Properties of Magnetic Dot Array with Soft Magnetic Underlayer”, Journal of Japan Society of Applied Magnetics, vol.30, No.2, pages 112-115, 2006 reference).
In sample A, which is partially bonded, exchange coupling works between the dots, which works in a direction that cancels out the magnetostatic interaction between the dots, so that the slope of the remanent magnetization curve increases as shown in the figure. Can be interpreted. That is, the coupling between dots can alleviate the influence of magnetostatic interaction and increase the slope of the remanent magnetization curve. This shows that the reversal magnetic field width can be reduced.

Surface recording density 2 Tbit / in For a ^2- bit pattern magnetic recording medium, the change in the remanent magnetization curve measured in the direction perpendicular to the film surface of the medium when a part of the track longitudinal direction end between bits is coupled is analyzed by micromagnetic simulation. An example of the investigation will be described.

FIG. 11 shows specifications of the bit pattern medium studied. FIG. 2 shows a model of the bit pattern medium for the medium C2. Except for the medium 1T, each track has 51 dots and 3 recording tracks with a track pitch of 25 nm. The connection between dots was performed by inserting 1 to 4 cubic elements each having a side of 2.5 nm.
For comparison, a 1 Tbit / in ² medium 1T in which the number of dots in the longitudinal direction is halved was also used. Each magnetic dot including the coupling portion was divided into cubic elements having a side of 2.5 nm, and the exchange coupling worked between the cubic elements with an exchange stiffness constant A = 4.9 × 10 ⁻⁷ erg / cm. As a result, a very realistic simulation model including a non-simultaneous magnetization rotation mode in which the direction of magnetization differs within a dot or at a dot coupling portion.
The parameters of each cubic element are as follows: saturation magnetization Ms = 1000 emg / cm ³ , average perpendicular anisotropy magnetic field H _k = 18 kOe, anisotropic dispersion (standard deviation) σH _k = 15% between elements, anisotropy axis The orientation dispersion σθ = 2 degrees from the vertical direction was introduced.
A soft magnetic backing layer provided via a nonmagnetic intermediate layer having a thickness of 1 nm was taken into the calculation as a mirror image layer. The calculation is performed by the energy balance method, and time dependence is not considered. Therefore, the obtained residual magnetization curve can be regarded as a magnetization behavior in a short time corresponding to the recording process.
Under these conditions, the perpendicular remanent magnetization curve was obtained by simulation. “Advanced Recording Model, ver. 6” from Euxine Technologies (Dayton, Ohio, USA) was used as simulation software.
FIG. 3 shows the obtained remanent magnetization curve. Here, the remanent magnetization is normalized by a saturation value. Medium 1T is a curve of a medium corresponding to 1 Tbit / in ² density with a wide bit interval (only this medium is H _k = 16 kOe), and medium C0 is a curve of a medium corresponding to 2 Tbit / in ² density with a small bit interval, , Media C1 to C4 show the curves of the media in which the dots are connected by 1 to 4 cubic elements, respectively.
The reversal magnetic field width, which is the difference between the remanent magnetization reversal start magnetic field H _nr and the residual saturation magnetic field H _sr , is 4.2 kOe for the medium T1 with a wide dot interval, whereas it is 7 for the medium C0 with a narrow dot interval. .8 kOe and doubled. This is due to the magnetostatic interaction between the dots as described above.
However, in the medium C1 having the same dot arrangement as that of the medium C0 and connecting the dots with one cubic element, the reversal magnetic field width is reduced to 6.0 kOe. Furthermore, the media C2 and C4 connected by two and four cubic elements showed a significant decrease to 3.6 kOe and 0.3 kOe, respectively. These indicate that the exchange coupling between dots works just the opposite of the magnetostatic interaction.

Comparative example

For the medium 1T and medium C0 corresponding to the surface recording densities 1 Tbit / in ² and 2 Tbit / in ² from the bit pattern medium shown in the second embodiment, the shift margins in the longitudinal direction and the track width direction of the head magnetic field in recording are provided. An example examined by simulation will be described.
As in Example 2, “Advanced Recording Model, ver. 6” from Euxine Technologies (Dayton, Ohio, USA) was used as simulation software. As a recording head magnetic field, a shield planar head (K. Ise, S. Takahashi, K. Yamakawa, and N. Honda, “New Shielded Single-Pole Head with Plane Structure. , Pp. 2422-2424, 2006) was used to analyze the magnetic field distribution obtained by electromagnetic field analysis software (“Maxwell 3D” from Ansoft (Pittsburgh, PA, USA)).
FIG. 4 shows the track length at the magnetic dot position of the medium when the magnetic pole track width is 14 nm, the magnetic pole thickness is 45 nm, the shield gap length is 12 nm, the shield height is 25 nm, and the distance between the magnetic pole tip surface and the soft magnetic layer surface is 12 nm. The vertical direction magnetic field distribution of a direction (Down track direction) and a width direction (Cross track direction) is shown. The figure shows the case where the magnetomotive force of the head is 60 mAT.
FIG. 5 shows 1016 kFCI (magnetic flux reversal / inch) and 2032 kFCI rectangular wave signals for the head magnetic pole tip surface and medium magnetic dot surface spacing for media 1T and C0, respectively, and track the switching timing of the head magnetic field. The result of checking the error rate when recording was performed by shifting in the longitudinal direction and the recording pattern was not performed normally is shown.
In the medium 1T, a normal recording pattern was obtained even when the timing was shifted in the range of 20.5 nm. However, in the medium C0 having a double dot density, a shift margin of 2.5 nm that is much narrower than half of the medium 1T. It became. This is because, as shown in FIG. 3 of Example 2, in the medium C0, the magnetostatic interaction between dots is increased and the reversal magnetic field width is increased.
Further, when the writing rate to the adjacent track due to the deviation of the head magnetic field in the track width direction was examined, as shown in FIG. 6, the track width direction shift margin also decreased from 6.5 nm to 5.0 nm of the medium 1T. did. This is thought to be due to the fact that the dot spacing is narrowed and the magnetostatic interaction between the dots is increased.
In any case, if the dot interval is made larger than the surface recording density 1 Tbit / in ² , the shift margin of the head magnetic field in the track longitudinal direction and the width direction is reduced, making it impossible to realize a high-density recording system.

As in the comparative example, for a bit pattern medium corresponding to a surface recording density of 2 Tbit / in ² , the shift margins in the longitudinal direction and the track width direction of the head magnetic field in recording are simulated by simulation when the magnetic dots are partially coupled. An example of the investigation will be described.
Similarly to the comparative example, “Advanced Recording Model, ver. 6” by Euxine Technologies (Dayton, Ohio, USA) as simulation software and shield planar head (K. Ise, S. Takahashi, K., K.) as a recording head magnetic field. Yamakawa, and N. Honda, “New Shielded Single-Pole Head With Planar Structure,” IEEE Transactions on Magnetics, Vol.42, No.10, p.42, No.10, p. Distribution was used.
As in the comparative example, the head has a magnetic pole track width of 14 nm, a magnetic pole thickness of 45 nm, a shield gap length of 12 nm, a shield height of 25 nm, a magnetic pole tip surface-soft magnetic layer surface distance of 12 nm, and the magnetomotive force of the head is the same. 60 mAT.
For the media C1 to C4 in which the dots are partially coupled, the head magnetic pole tip surface-medium magnetic dot surface spacing is set to 6 nm, and the 2032 kFCI rectangular wave signal is shifted in the track longitudinal direction by switching the head magnetic field switching timing. The error rate was recorded and the recording pattern was not performed normally.
The results are shown in FIG. In the media C1 to C3 having the number of couplings of 1 to 3, a timing deviation margin larger than that of the medium C0 of the comparative example was obtained. This is because, as shown in FIG. 3 of the second embodiment, the width of the reversal magnetic field is reduced by introducing the coupling between dots. However, if the coupling becomes too large, the magnetization of the magnetic dots tends to point in the same direction, and the timing shift margin is reduced.
Further, when the writing rate to the adjacent track due to the deviation of the head magnetic field in the track width direction was examined, as shown in FIG. 8, all the media combined with dots obtained a shift width direction shift margin larger than that of the medium C0. . This is considered to be due to magnetic anisotropy being induced in the longitudinal direction due to the coupling of dots in the longitudinal direction of the track.
As shown in FIG. 9, the anisotropy is induced in the track longitudinal direction due to the difference in the applied magnetic field angle dependence of the remanent coercive force (switching magnetic field) depending on the applied direction in the patterned medium C2 having the coupling between dots. I have confirmed that.
FIG. 10 shows changes in the track longitudinal direction timing shift margin and the track width direction shift margin depending on the inter-dot coupling cross-sectional area ratio in the pattern medium (medium C0 to C4) of 2 Tbit / in ² arrangement. It can be seen that the track width direction shift margin does not decrease as the coupling between dots increases, but the track longitudinal direction shift margin increases when the coupling cross-sectional area ratio is 30% or less of the dot cross-sectional area.
In particular, a large effect was obtained at an area ratio of 10-25%. Thus, it has become clear that the shift margin in the track longitudinal and width directions can be increased by partially coupling the magnetic dots.

The figure which shows the change by the dot coupling | bonding of the perpendicular direction residual magnetization curve of a perpendicular magnetic anisotropic dot pattern film. Medium A: 25% area ratio combined, medium B: complete separation. The figure (medium C2) which shows the structure of a perpendicular magnetic anisotropic bit pattern medium. A nonmagnetic intermediate layer having a thickness of 1 nm is provided between the magnetic dots and the soft magnetic backing layer. The figure which shows the change by the coupling area between dots of the perpendicular direction residual magnetization curve of a perpendicular magnetic anisotropic bit pattern film obtained by computer simulation. The figure which shows the cross-sectional structure of the magnetic head used for recording simulation, and the track length and width direction distribution of the generated magnetic field. Dependence of the recording error rate on the center track when the switching timing of the rectangular wave signal recording magnetic field is shifted in the longitudinal direction of the track in the 1 Tbit / in ² and 2 Tbit / in ² layout pattern media FIG. The figure which shows the shift amount dependence of the writing rate to an adjacent track when the recording magnetic field is shifted in the track width direction in the patterned media of 1 Tbit / in ² arrangement and 2 Tbit / in ² arrangement. Differences in the timing shift amount dependence of the recording error rate at the center track when the switching timing of the rectangular wave signal recording magnetic field is shifted in the track longitudinal direction on a patterned medium with 2 Tbit / in ² layout FIG. The figure which shows the difference by the coupling area between dots of the shift amount dependence of the writing rate to an adjacent track when the recording magnetic field is shifted to the track width direction in the pattern medium of 2 Tbit / in ² arrangement. The figure which shows the difference by the applied direction of the applied magnetic field angle dependence of the residual magnetization coercive force (switching magnetic field) in the bit pattern medium which has the coupling between dots in the track longitudinal direction. The figure which shows the change by the cross-sectional area ratio between dots of a track longitudinal direction timing shift margin and a track width direction shift margin in the pattern medium of 2 Tbit / in ² arrangement. The figure which shows the item of the medium used by the Example and the comparative example.

Claims (2)

In a patterned magnetic recording medium including magnetic dots having a magnetic anisotropy in the vertical direction and formed of a dot-patterned magnetic film, a part of the magnetic dots is coupled in the track longitudinal direction, and the magnetic A bit pattern magnetic recording medium characterized in that the cross-sectional area of the connecting portion between dots is 30% or less of the maximum cross-sectional area of the magnetic dots in the track width direction and the surface recording density is ² Tbit / in ² or more . 2. The bit pattern magnetic recording medium according to claim 1, wherein the cross-sectional area of the coupling portion between the magnetic dots is 10 to 25% of the maximum cross-sectional area of the magnetic dots in the track width direction.