Method and device for recording and reproduction, and magnetic recording medium

The present invention relates to a recording / reproducing method and a recording / reproducing apparatus and a magnetic recording medium, and more particularly to a recording / reproducing method and a recording / reproducing apparatus suitable for a magnetic recording medium having a high recording density, and a magnetic recording medium.

In recent years, the improvement of recording density in magnetic recording media such as magnetic recording tapes and magnetic disks has been remarkable. Therefore, various techniques related to the recording / reproducing device have been proposed and put into practical use in response to the increase in the recording density of the recording medium. For example, various technologies have been proposed and put into practical use, such as the adoption of an MR head as a recording / playback head and the improvement of the interface between a recording medium and the head. Furthermore, in terms of signal processing technology, in order to recover from the deterioration of the S / N ratio due to high-density recording, the partial response (PR) method and maximum likelihood decoding (ML: Maximum) are used. The PRML method combined with the Likelihood) method has been put into practical use in a recording / playback device using a recording medium such as a magnetic disk, a digital VTR, a magnetic tape for computer backup, or an optical disk (see Patent Document 1). This PRML signal processing method is PR4ML (PR (1,0, -1) ML), EPR4ML (PR (1,1, -1, -1) ML) according to the number of terms in the signal sequence to be equalized. , EEEPR4ML (PR (1,2,0, -2, -1) ML), EEEPR4ML (PR (1,3,2, -2, -3, -1) ML) and various other methods are known. There is.

Then, if the optimum partial response signal processing is applied according to the characteristics of the magnetic material to be used, the information signal recorded at high density on the magnetic recording medium can be restored at a low error rate, which is effective. For example, a magnetic recording medium having a magnetic layer containing a hexagonal ferrite as a magnetic material has a characteristic that the reproduction output in high-density recording is high and the noise is low. However, since hexagonal ferrite has a vertical magnetization component even in in-plane orientation or non-orientation due to its crystal structure, the isolated inversion regeneration waveform is perpendicular to the in-plane orientation isolated inversion regeneration waveform. It becomes a peculiar waveform by adding the isolated inversion reproduction waveform of, and shows the asymmetric waveform as shown in FIG. 2, for example. For the peculiar isolated inversion reproduction waveform obtained when such hexagonal ferrite is used as a magnetic material, the conventional PRML signal processing optimized for the magnetic recording medium in which the magnetization in the in-plane direction is recorded is applied. However, it was not possible to take advantage of the characteristics peculiar to hexagonal ferrite magnetic materials, such as optimum signal processing, high reproduction output in high-density recording, and low noise.<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2002-157827 (paragraph 0051, Fig. 10)</text></patcit>

<p> Therefore, an object of the present invention is to provide a recording / reproducing method and a recording / reproducing device optimized for a partial response signal processing method when reproducing an information signal from a magnetic recording medium having a high recording density.</p>

<p> In order to solve the above problems, the present invention is a recording / reproduction method in which an information signal recorded on a magnetic recording medium is equalized, demodulated and reproduced by a partial response signal processing method, and is isolated and inverted reproduced from the magnetic recording medium. When γ indicating the asymmetry of the reproduced waveform has a waveform in which γ&gt; 0, the coefficient term of the partial response (1, a)₁, a₂, ..., a_mIf (m = 2n or 2n + 1: n is an integer of 1 or more) satisfies the following equation (1) or equation (2) and has a waveform in which γ is γ &lt;0, the partial response Provided is a recording / reproduction method characterized in that equalization and demodulation is performed under the condition that the coefficient term of the above satisfies the following equation (3) or equation (4).<maths num="5"><img file="JP2005293750A_D0001.tif" /></maths></p><p> In this recording / reproducing method, the coefficient term (1, a) of the partial response depends on the asymmetry of the isolated inverted reproduction waveform reproduced from the magnetic recording medium.₁, a₂, ..., a_mThe sum of the first half terms and the sum of the second half terms of (m = 2n or 2n + 1: n is an integer of 1 or more) are the above equations (1) and (2) or the above equations (3) and equations. By equalizing and demodulating so as to satisfy (4), the optimum PRML signal processing can be applied to the characteristics of the hexagonal ferrite magnetic material.</p><p> Further, the present invention is a recording / playback apparatus having an equalization means for equalizing an information signal recorded on a magnetic recording medium by a partial response signal processing method and a demodulation means for demodulating the equalized information signal. When the demodulation means has a waveform in which γ indicating the asymmetry of the isolated inverted reproduction waveform reproduced from the magnetic recording medium is γ&gt; 0, the demodulation means is the information signal equalized by the equalization means. Partial response coefficient term for (1, a)₁, a₂, ..., a_mWhen (m = 2n or 2n + 1: n is an integer of 1 or more) is demodulated under the condition that the above equation (1) or (2) is satisfied, and the waveform has a waveform in which the γ is γ &lt;0. , The demodulation means is a coefficient term (1, a) of a partial response for the information signal equalized by the equalization means.₁, a₂, ..., a_mProvided is a recording / playback apparatus characterized in that (m = 2n or 2n + 1: n is an integer of 1 or more) is demodulated under the condition that the following equation (3) or equation (4) is satisfied.</p><p> In this recording / reproducing device, the sum of the first half terms of the coefficient term of the partial response for the information signal equalized by the equalizing means according to the asymmetry of the isolated inverted reproduction waveform reproduced from the magnetic recording medium. Hexagonal ferrite by demodulating the information signal so that the sum of the latter terms satisfies the above equations (1) and (2) or the above equations (3) and (4). Partial response signal processing that is optimal for the characteristics of the magnetic material can be performed.</p><p> In the present invention, γ indicating the asymmetry of the isolated inverted reproduction waveform reproduced from the magnetic recording medium is an index indicating whether the peak position of the isolated inverted reproduced waveform is biased to the first half waveform portion or the second half waveform portion. For example, when the half-value width of the left-right asymmetric isolated inversion playback waveform shown in FIG. 2 is PW50, the width on the right side of the half-value width PW50 is PW1, and the width on the left side is PW2, it is expressed by the following equation (5). The ratio to be used. γ (%) = [[(PW1)-(PW2)] ÷ (PW50)] × 100 (5)</p><p> Furthermore, the present invention provides a magnetic recording medium used in the recording / reproducing device.</p>

<p> The recording / reproducing method and recording / reproducing apparatus of the present invention perform partial response signal processing optimal for the characteristics of the magnetic material forming the magnetic layer of the magnetic recording medium when reproducing the information signal recorded on the magnetic recording medium. A reproduction signal with a high S / N ratio can be obtained from a magnetic recording medium on which information is recorded at high density. Therefore, the reproduced signal can be obtained at a low error rate. In particular, in the case of a magnetic recording medium using a hexagonal ferrite magnetic material, it is possible to take advantage of the characteristics of the hexagonal ferrite magnetic material that the reproduction output in high-density recording is high and the noise is low.</p><p> Further, the magnetic recording medium of the present invention exhibits the characteristics of the magnetic material and provides high-density information by performing partial response signal processing that is optimal for the characteristics of the magnetic material forming the magnetic layer in the recording / reproducing device. Can be recorded, and a reproduction signal with a high S / N ratio can be obtained. Therefore, the reproduced signal can be obtained at a low error rate.</p>

Hereinafter, the recording / reproducing method, the recording / reproducing apparatus, and the magnetic recording medium of the present invention will be described. The magnetic recording medium of the present invention has a magnetic layer containing a magnetic material on which an information signal is written by a recording head of a recording / reproducing device on one or both surfaces of a support, and a non-magnetic layer is provided under the magnetic layer. Have. As a specific example of this magnetic recording medium, an information signal is remanently magnetized by a magnetic recording head on a magnetic layer containing a magnetic material such as a magnetic tape, a magnetic disk (hard disk, flexible disk), or a ferromagnetic alloy powder containing Fe as a main component. Examples thereof include a recording medium capable of recording in a form.

Supports include various synthetic resins such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, polyimide, polysulfone, and polyethersulfone, and films and plates made of metals such as aluminum and stainless steel. Etc. can be appropriately molded according to the use, form, etc. of the magnetic recording medium.

When the magnetic recording medium is in sliding contact with the recording head or the reproduction head, it is preferable that the magnetic recording medium has a back layer on the surface of the support opposite to the magnetic layer to facilitate the sliding contact. Further, the magnetic recording medium may have a layer other than the non-magnetic layer, the magnetic layer, and the back layer. For example, it may have a soft magnetic layer containing a soft magnetic powder, a second magnetic layer, a cushion layer, an overcoat layer, an adhesive layer, and a protective layer. These layers can be provided at appropriate positions so that their functions can be effectively exerted. The thickness of the magnetic layer is preferably 10 to 300 nm, more preferably 10 to 200 nm, and particularly preferably 10 to 100 nm. The non-magnetic layer can be 0.5 to 3 μm. The thickness of the non-magnetic layer is preferably thicker than that of the magnetic layer.

As the magnetic material, ferromagnetic metal powder or hexagonal ferrite powder is used. Specific examples of the ferromagnetic metal powder include simple metals or alloys such as Fe, Ni, Fe-Co, Fe-Ni, Co-Ni, and Co-Ni-Fe, and the range is 20% by mass or less of the metal component. Within, aluminum, silicon, sulfur, scandium, titanium, vanadium, chromium, manganese, copper, zinc, ittrium, molybdenum, rhodium, palladium, gold, tin, antimony, boron, barium, tantalum, tungsten, renium, silver, lead. , Phosphorus, lantern, cerium, praseodymium, neodymium, tellurium, bismuth, etc. can be included. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide.

The average particle size of the ferromagnetic powder is preferably 20 to 60 nm. When the ferromagnetic powder used is needle-shaped or the like, the average major axis length is 30 to 100 nm, preferably 35 to 90 nm, and more preferably 40 to 80 nm. By setting the average major axis length to 100 nm or less, noise can be reduced and a good signal SN can be obtained. In addition, a good holding force Hc can be secured by setting the average major axis length to 30 nm or more. The average acicular ratio of the powder particles is 3 to 10, preferably 3 to 8, and more preferably 4 to 8. In the case of a plate shape, the average powder size is represented by the average plate diameter, preferably 25 to 35 nm, and the average plate shape ratio is preferably 2 to 5.

In addition, ferromagnetic metal powder is S_BET(BET specific surface area) is usually 40-80m²/ g, preferably 50-70m²It is / g. The crystallite size is usually 10 to 25 nm, preferably 11 to 22 nm. The pH of the ferromagnetic metal powder is preferably 7 or more.

These ferromagnetic metal powders can be produced according to known methods. The shape of the ferromagnetic metal powder is not particularly limited, but needle-shaped, granular, dice-shaped, rice-granular and plate-shaped ones are usually used. In particular, it is preferable to use a needle-shaped ferromagnetic powder.

The coercive force Hc of the ferromagnetic metal powder is preferably 144 to 300 kA / m, more preferably 160 to 224 kA / m. The saturation magnetization is 85 ~ 150A m.²/ kg is preferable, 100 ~ 130A m²/ kg is even more preferred.

Examples of the hexagonal ferrite include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite and various substituents thereof, for example, Co-substituted product. Specific examples thereof include magnetoplumbite-type barium ferrite and strontium ferrite, magnesium-plumbite-type ferrite whose particle surface is coated with spinel, and composite magnesium-type barium ferrite and strontium ferrite containing a part of spinel phase. Al, Si, S, Nb, Sn, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, W, Re, Au, Bi, It may contain atoms such as La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, B, Ge and Nb. Generally Co-Zn, Co-Ti, Co-Ti-Zr, Co-Ti-Zn, Ni-Ti-Zn, Nb-Zn-Co, Sn-Zn-Co, Sn-Co-Ti, Nb-Zn, etc. It is possible to use a product to which the above elements have been added. It is also possible to use a W-type hexagonal ferrite. Further, it may contain impurities peculiar to the raw material / manufacturing method. These hexagonal ferrites are used in the form of hexagonal plate powder.

By setting the average plate diameter of the hexagonal ferrite magnetic powder to 50 nm or less and the average thickness to 15 nm or less, noise can be reduced and high S / N can be obtained when reproducing at high density, especially with an MR head. The specific surface area by the BET method is usually 30 to 200 m.²/ g, 50 ~ 100m²/ g is preferred. The specific surface area roughly matches the arithmetically calculated value from the powder plate diameter and plate thickness. The narrower the distribution of plate diameter and plate thickness, the more preferable. The distribution is often not a normal distribution, but when calculated and expressed as the standard deviation with respect to the powder size, σ / (average plate diameter or average plate thickness) = 0.1 to 0.5. In order to sharpen the powder size distribution, the powder production reaction system is made as uniform as possible, and the produced powder is subjected to distribution improvement treatment. For example, a method of selectively dissolving ultrafine powder in an acid solution is also known. In the vitrification crystallization method, heat treatment is performed a plurality of times to separate nucleation and growth to obtain a more uniform powder. The coercive force Hc measured with the magnetic powder can be prepared up to about 40 to 400 kA / m, but 144 to 300 kA / m is preferable. High Hc is advantageous for high density recording, but is limited by the ability of the recording head. Hc can be controlled by powder size (plate diameter / thickness), type and amount of contained elements, element substitution sites, powder formation reaction conditions, and the like.

Saturation magnetization σS of hexagonal ferrite powder is 30 ~ 70A m²/ kg is preferred. σS tends to become smaller as the powder becomes finer.

In the present invention, a coating type barium ferrite (BaFe) magnetic layer in which a dispersion liquid containing barium ferrite powder of hexagonal ferrite is coated on a support to form a magnetic layer, particularly barium ferrite magnetism having a plate diameter of 40 nm or less. A magnetic recording medium having a coated barium ferrite magnetic layer using a body is effective because it has excellent reproduction output in high-density recording (particularly, line recording density exceeding 100 kfci) and has low noise characteristics. ..

Generally, in a magnetic recording medium using iron oxide or cobalt-containing ferromagnetic iron oxide as the magnetic material, the isolated inverted reproduction waveform to be reproduced shows asymmetry of γ0, and hexagonal ferrite is used as the magnetic material. In the magnetic recording medium that was used, the isolated inverted reproduction waveform reproduced shows an asymmetry of γ&gt; 0. Further, in a magnetic recording medium having a magnetic layer formed by a vapor deposition method, the isolated inverted reproduction waveform to be reproduced shows a specific symmetry of γ &lt;0. Therefore, according to this asymmetry, the partial response signal processing is equalized so as to satisfy the conditions represented by the above (1) and (2), or (3) and (4), thereby performing the magnetic recording medium. Optimal partial response signal processing can be performed according to the magnetic material forming the magnetic layer.

That is, in the recording / reproducing method and the recording / reproducing apparatus of the present invention, when reproducing an information signal from the magnetic recording medium, first, the analog signal read from the magnetic recording medium by the recording / reproducing head is used as the magnetic recording medium. It can be estimated in advance whether γ, which indicates the asymmetry of the isolated inversion reproduction waveform, is γ&gt; 0, γ0, or γ &lt;0, depending on the magnetic material. Therefore, in the recording / reproducing method and the recording / reproducing apparatus of the present invention, when the γ indicating the asymmetry of the isolated inverted reproduction waveform to be reproduced has a waveform of γ&gt; 0 depending on the magnetic material of the magnetic recording medium used. Is the coefficient term of the partial response (1, a)₁, a₂, ..., a_mThe information signal read from the magnetic recording medium by the partial response signal processing method under the condition that (m = 2n or 2n + 1: n is an integer of 1 or more) satisfies the above equation (1) or equation (2). The equalized and equalized signal is demodulated to restore the original signal. Further, when the γ indicating the asymmetry of the isolated inversion reproduction waveform has a waveform in which γ &lt;0, the coefficient term (1, a) of the partial response is obtained.₁, a₂, ..., a_mThe information signal read from the magnetic recording medium by the partial response signal processing method under the condition that (m = 2n or 2n + 1: n is an integer of 1 or more) satisfies the above equation (3) or equation (4). The equalized and equalized signal is demodulated to restore the original signal. In this way, the optimum partial response signal processing, that is, PR4ML (PR (1,0, -1) ML), EPR4ML (PR (1,1, -1,-), depending on the asymmetry of the isolated inversion playback waveform. 1) ML), EPPR4ML (PR (1,2,0, -2, -1) ML), EEEPR4ML (PR (1,3,2, -2, -3, -1) ML), etc. By selecting whether to perform equalization processing by the response signal processing method, it is possible to restore the reproduced signal at a low error rate.

Next, taking a magnetic recording medium having a magnetic layer containing barium ferrite as a magnetic material as an example, the recording / reproducing method and the recording / reproducing apparatus of the present invention will be described with reference to FIGS. FIG. 1 shows a configuration example of a recording / reproducing device according to the present invention, in which the recording / reproducing device 10 includes a precoder 11, a recording / reproducing amplifier 12, a recording head 13, a reproduction head 14, and an equalizer (equalization). Means) 15, a maximum likelihood decoder 16, and a decoder (demodulation means) 17 are provided.

By placing the precoder 11 before the data recording, it is possible to prevent the propagation of errors that occur during demodulation.

The recording / reproduction amplifier 12 amplifies the signal encoded by the precoder 11 and also amplifies the signal generated by the reproduction head 14 described later. The recording head 13 magnetizes a barium ferrite magnetic material contained in the magnetic layer of the magnetic recording medium 20 to record data having a predetermined clock period on the magnetic recording medium 20.

The reproduction head 14 is in sliding contact with the magnetic layer of the magnetic recording medium 20, reads a change in the magnetization of the magnetic layer, and obtains an analog reproduction signal. This analog signal is a signal obtained by differentiating the signal recorded on the magnetic layer of the magnetic recording medium 20, and is represented by the transmission characteristic (1-D).

FIG. 2 shows an example of the waveform of the analog signal generated by reading by the playback head 14. Here, an isolated inverted reproduction waveform generated at the rising timing of the pulse signal recorded on the magnetic recording medium 20 will be described as an example.

The isolated inversion reproduction waveform shown in FIG. 2 has a peak in the positive direction, and the left and right of the peak are asymmetric. And, in this isolated inversion reproduction waveform, the width PW1 on the right side of the half width PW50 of the peak value is larger than the width PW2 on the left side. This is the sum of the in-plane oriented magnetization component and the perpendicular magnetization component peculiar to barium ferrite.

In FIG. 2, the isolated inverted reproduction waveform having a peak in the positive direction is shown as the waveform of the analog signal, but in reality, the waveform of the analog signal has two isolated inverted reproductions having peaks in the positive direction and the negative direction. It is composed of overlapping waveforms. This is because the isolated inversion reproduction waveform having a peak in the negative direction also occurs at the timing of the falling edge of the pulse signal recorded on the magnetic recording medium 20.

The equalizer 15 (equalizing means) equalizes the signal transferred from the playback head 14 via the recording / playback amplifier 12. The transmission characteristics of PR (1, a, b, c, d, e, ...) are 1 + a D + b D²+ c D³+ d D⁴+ e D⁵+ = (1-D) (1 + f₁ D + f₂ D²+ f₃ D³+ f₄ D⁴At the time of + ...), specifically, the equalizer 15 has a transmission characteristic of 1 + f.₁ D + f₂ D²+ f₃ D³+ f₄ D⁴Equalize as represented by + ...

The maximum likelihood decoder 16 identifies the data equalized by the equalizer 15. Maximum likelihood decoding is a well-known technique for detecting the most probable data sequence when recording and reproducing data with a correlation. Then, the decoder 17 decodes the equalized signal into the original data (for example, (0,1,0)). As a result, the recorded data recorded on the magnetic recording medium 20 can be correctly restored to the original data.

Hereinafter, an example in which the recording / reproducing method of the present invention is specifically performed will be shown.

&lt;Prescription of coating liquid for BaFe magnetic layer&gt; Barium ferrite magnetic powder 100 parts Polyurethane resin 14 parts Mass average molecular weight: 10000 Sulfonic acid Functional group: 0.05meq / g Polishing agent 8 parts Carbon black (particle size: 0.015 μm) 0.5 parts # 55 (manufactured by Asahi Carbon Co., Ltd.) Stearate 0.5 part Butyl stearate 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 100 copies

&lt;Prescription of coating liquid for non-magnetic layer&gt; Non-magnetic powder: 100 parts of α-iron oxide Average primary particle size: 0.09 μm, specific surface area by BET method: 50 m²/ g pH: 7 DBP Oil absorption: 27 ~ 38ml / 100g, Surface treatment layer: Al₂O₃Is present in 8% by mass with respect to the entire particle Carbon Black 25 parts Conductex SC-U (Columbian Carbon) Vinyl chloride copolymer: MR104 (Nippon Zeon) 13 parts Polyurethane resin: UR8200 (Toyo Boseki 9) 5 parts Phenylphosphonic acid 3.5 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 205 parts Cyclohexanone 135 copies

&lt;Manufacturing of tape&gt; Each component was kneaded with a kneader according to the above formulation of the coating liquid. The obtained kneading liquid was pumped through a horizontal sand mill containing an amount of 1.0 mmφ zirconia beads filled in an amount of 80% of the volume of the dispersion part, and the liquid was passed at 2000 rpm for 120 minutes (substantially the time spent in the dispersion part). ) A dispersion treatment was performed to prepare a dispersion liquid for the magnetic layer and a dispersion liquid for the non-magnetic layer, respectively. To the obtained dispersion liquid for the magnetic layer, 3 parts of methyl ethyl ketone was further added and filtered using a filter having an average particle size of 1 μm to obtain a coating liquid for forming the magnetic layer. Further, 2.5 parts of polyisocyanate and 3 parts of methyl ethyl ketone are added to the dispersion liquid for the non-magnetic layer, and the mixture is filtered using a filter having an average particle size of 1 μm to obtain a coating liquid for forming the non-magnetic layer. Prepared.

The obtained coating liquid for forming a non-magnetic layer was applied onto a polyethylene naphthalate base having a thickness of 4 μm so as to have a thickness of 1.5 μm after drying, and dried to form a non-magnetic layer. After that, a coating liquid for forming a magnetic layer is sequentially applied on the non-magnetic layer so that the thickness of the magnetic layer becomes 30 to 210 nm, and the magnetic layer has a magnetic force of 600 mT while still in a wet state. A cobalt magnet and a solenoid with a magnetic force of 600 mT align the BaFe magnetic material in the magnetic layer in-plane, and a 600 mT cobalt magnet applies a magnetic field in the vertical direction to orient the magnetic material diagonally. The vertical magnetic field was retained until drying was complete. Then, the treatment was performed on a 7-stage calendar at a temperature of 90 ° C. and a linear pressure of 300 kg / cm (294 kN / m). Then, the back layer forming layer coating liquid of the following formulation was applied to the surface opposite to the surface on which the non-magnetic layer and the magnetic layer were formed to form a back layer having a thickness of 0.5 μm, and a web raw fabric was obtained.

Coating liquid for back layer formation Carbon black (average particle size: 17 nm) 100 parts Calcium carbonate (average particle size: 40 nm) 80 parts α-alumina (average particle size: 200 nm) 5 parts Dispersion liquid (nitrocellulose resin, polyurethane resin, poly Isocyanate)

As described above, a web raw fabric having a non-magnetic layer and a magnetic layer on one surface and a back layer on the other surface is slit to a width of 3.8 mm, and a non-woven fabric is provided in a device provided with a feeding portion and a winding portion of the slit product. The razor blade was attached so as to press against the magnetic surface, and the surface of the magnetic layer was cleaned with a tape cleaning device to obtain a magnetic tape having a magnetic layer containing a BaFe magnetic material.

Data waveforms having different standardized linear densities K = (PW50) / (bit length) are recorded on a magnetic tape having a magnetic layer containing a BaFe magnetic material using a recording / reproducing device having the configuration shown in FIG. , 3 types of playback samples were prepared. For the isolated inversion reproduction waveform (γ = 22%) reproduced from each of these three types of magnetic tapes, PR (1, a, b, c) ML method, PR (1, a, b, c, d) ML method, PR (1, a, b, c, d, e) By ML method, the error rate with a coefficient where the absolute value of the sum of the first half of the characteristic term is smaller than the absolute value of the sum of the second half of the characteristic term is calculated. It was measured. In addition, the normal PRML method (= PR (1,1, -1, -1) ML method, PR (1,2,0, -2, -1) ML method, PR (1,3,2, -2) , -3, -1) The error rate in the ML method) was also measured.

The same applies to magnetic tapes using metal (ferromagnetic alloy powder containing Fe as the main component, γ = 3%) and ME (magnetic layer by vapor deposition method, γ = -13%) as magnetic materials. And measured the error rate. The results obtained are shown in Table 1.

<tables num="1"><img file="JP2005293750A_D0002.tif" /></tables> From the results shown in Table 1, barium ferrite (BaFe) magnetic material with γ (= 22%)&gt; 0 and metal (ferromagnetic alloy powder containing Fe as the main component) magnetic material with γ (= 3%)&gt; 0. It was found that the error rate was reduced in the case of the above equation (1) or (2) in the magnetic tape using. Further, it was found that the error rate was reduced in the case of the above formula (3) or (4) in the ME (magnetic layer by the vapor deposition method) magnetic tape in which γ (= -13%) &lt;0.

<figref num="1">It is a block diagram which shows the structural example of the recording / reproduction apparatus of this invention.</figref><figref num="2">It is a figure which shows an example of the isolated inversion reproduction waveform.</figref><figref num="3">It is a figure which shows an example of the signal sequence in partial response signal processing.</figref>

Code description

10 Recording / playback device 11 Precoder 12 Recording / playback amplifier 13 Recording head 14 Playback head 15 Equalizer 16 Maximum likelihood decoder 17 Decoder 20 Magnetic recording medium