WO1995035566A1 - Support multicouches d'enregistrement magnetique pour enregistrements a hautes densites lineaires de bits - Google Patents

Support multicouches d'enregistrement magnetique pour enregistrements a hautes densites lineaires de bits Download PDF

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Publication number
WO1995035566A1
WO1995035566A1 PCT/US1995/004962 US9504962W WO9535566A1 WO 1995035566 A1 WO1995035566 A1 WO 1995035566A1 US 9504962 W US9504962 W US 9504962W WO 9535566 A1 WO9535566 A1 WO 9535566A1
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WO
WIPO (PCT)
Prior art keywords
layer
magnetic recording
magnetizable
coercivity
recording medium
Prior art date
Application number
PCT/US1995/004962
Other languages
English (en)
Inventor
Richard E. Fayling
Original Assignee
Minnesota Mining And Manufacturing Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Minnesota Mining And Manufacturing Company filed Critical Minnesota Mining And Manufacturing Company
Publication of WO1995035566A1 publication Critical patent/WO1995035566A1/fr

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/64—Record carriers characterised by the selection of the material comprising only the magnetic material without bonding agent
    • G11B5/66—Record carriers characterised by the selection of the material comprising only the magnetic material without bonding agent the record carriers consisting of several layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
    • G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
    • G11B5/716—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by two or more magnetic layers

Definitions

  • the invention relates to a magnetic recording medium for recording binary data.
  • the invention is specifically concerned with a multi-layer magnetic recording medium that enables binary data to be recorded at increased linear bit densities without pulse crowding.
  • NRZ non return to zero
  • MFM binary or other magnetic recording technique
  • the Kougami patent says: "In general, in prior-art methods of recording digital signals, a rectangular wave is used as the magnetic head driving current.... It is well known that the playback signal becomes a mountain-like pulse waveform with respect to one reversal of the driving current" (col. 1, lines 21-31). The Kougami patent shows that a playback signal which indicates "1” does "not become zero at the centers of the adjacent information bits of '0', as shown at numerals 4 and 5 in FIG. 1(c)" (col. 1, lines 48-54).
  • U.S. Pat. No. 4,786,988 (Kobayashi) concerns a high-speed contact printing technique for duplicating video information recorded on a master tape and specifically concerns control signals on a sub-master tape which is duplicated from the master to obtain a mirror of the master signals from which "slave tapes" can be made by contact duplication.
  • the control signals (which are binary write signals generated from NRZ write current) are re-formed as shown in Fig. 1(B) "to lower the spike noise components Nl, N2, N3 and N4 conventionally produced at the leading and trailing edges of the differentiated control signal spikes reproduced from the slave tape as shown in FIG. 1(C)" (col. 4, lines 3-8).
  • FIGs. 1(B) are similar to the modified write signal of Fig. 10(b) of the above-discussed Kougami patent, but every leading edge of Kobayashi's write waveform is re-formed, not just those that are at least 1.5 times the bit period.
  • Figs. 3(A) to 3(E) of the Kobayashi patent "show some possible modifications to the waveform of the control signals to be recorded on the sub-master tape" (col. 5, lines 5-7).
  • Fayling I "Edge Profile Studies of Recorded Flux Transitions", IEEE Transactions on Magnetics, Vol. MAG-16, No. 3, Sept. 1980, pp 1249-1255 (here called “Fayling I”). Fayling I teaches that when a square-wave current pulse is recorded on magnetic recording tape that has a longitudinally oriented easy axis and has been premagnetized uniformly in the direction opposite to that of the head field, each flux transition produced in the medium normally has curved leading and trailing edges like those shown in several photographs. A second of these is Fayling et al.: "A Model for Overwrite Modulation in Longitudinal Recording", IEEE Transactions on Magnetics, Vol. MAG-20, No. 5, Sept.
  • Fayling IT illustrates in each of Figs. 1, 2 and 3 a series of magnetically recorded bits (flux transitions) as viewed from the side, showing a curved boundary at each edge of each flux transition.
  • Fayling III shows in Fig. 4 experimentally determined flux transition edge ("ft e") profiles for different He magnetic recording media which have a longitudinally oriented easy axis and have been premagnetized uniformly in the direction opposite to that of the head field. Fayling HI points out that the curvature of most of the illustrated ft e profiles approximate the form predicted by the Kariqvist equation. "The four pairs of flux transition profiles in Figure 4 ... show decreasing separation with increasing coercive force at recording head-to-medium spacing less than 0.25 mm" (p. 1214, first column).
  • Magnetic recording media are known wherein an outer layer is of lower coercivity than an inner layer.
  • the inner layer is of such high coercivity that it can be recorded with data which is not affected when an outer layer of lower coercivity is recorded or erased.
  • the two magnetizable layers do not function together as they do in the above- discussed multi-layer magnetic recording media.
  • the invention provides a novel magnetic recording medium designed to be recorded with binary data at higher linear bit densities than can be achieved with prior magnetic recording media.
  • the magnetic recording medium of the invention has at least two coextensive, contiguous magnetizable layers of differing coercivity (He) which function together in such a way that trailing f t e profiles which separate adjacent binary cells recorded on the medium are straighter than are trailing f t e profiles recorded on a magnetizable layer having a thickness equal to the total thickness of said at least two layers and only one of those coercivities.
  • trailing f t e profiles which separate adjacent binary cells recorded on the novel multi layer medium can be closer to perpendicular to the surface of the magnetizable layer than are trailing f t e profiles of prior magnetic recording media.
  • trailing f t e profiles which separate adjacent binary cells recorded on the novel multi layer medium can be closer to perpendicular to the surface of the magnetizable layer than are trailing f t e profiles of prior magnetic recording media.
  • the novel magnetic recording medium has at least two coextensive, contiguous magnetizable layers of differing coercivity (He) that function together.
  • the coercivity of the outer or surface magnetizable layer of the novel medium usually is less than that of an inner (adjacent) magnetizable layer.
  • the coercivity of the outer magnetizable layer is at least one-half the coercivity of the inner layer, preferably at least 70% that of the inner layer.
  • each magnetizable layer should be sufficiently high to afford stable recording, while being sufficiently low to be recordable at high frequency by recording heads now in common use.
  • the coercivity of each magnetizable layer should be at least 300 Oe, preferably from 500 to 2000 Oe.
  • Each magnetizable layer that covers another magnetizable layer should be as thin as is economically feasible so as to minimize the spacing between the head and the magnetizable layer it covers, preferably not greater than 10_mm in thickness, more preferably not greater than l_mm, and ideally less than 0.25_mm.
  • the innermost magnetizable layer can also be thin, because it normally would be difficult to magnetize it to a significant depth due to its spacing from the head.
  • Layers of magnetizable particles and nonmagnetizable binder can currently be made to provide a uniform, defect-free layer as thin as 100 nm and can be used for outer and inner layers of the novel magnetic recording medium.
  • magnetizable thin films such as can be made by vapor deposition, by sputtering, plating, etc. to have thicknesses from 10 to 1000 nm. Particularly useful thicknesses are from 15 to 50 nm.
  • FIG. 1 is an edge view of fragments of a magnetic recording head and a single-layer magnetic recording medium of an NRZ binary magnetic recording system of the prior art and shows idealized trailing f t e profiles of successive binary cells of the prior art
  • FIG. 2 is an enlarged fragmentary edge view of the same system as that of FIG. 1 except showing trailing f t e profiles of binary cells of the prior art recorded on four different magnetic recording media, each having a single recording layer of a different single magnetizable material;
  • FIG. 3 is an enlarged fragmentary edge view of the same system as that of FIG. 1 except using a multi-layer magnetic recording medium of the invention.
  • FIG. 4 is an edge view like that of FIG. 3 except using a different multi-layer magnetic recording medium of the invention.
  • a magnetic recording medium 10 which has a nonmagnetizable backing 11 and a single magnetizable layer 12, is driven at a constant velocity v in the direction of an arrow 17 across the gap between the pole tips 14 and 15 of an ordinary ring-type head and at a small head-to-medium spacing 18.
  • the magnetizable layer 12 Before being driven across the head, the magnetizable layer 12 has been erased to be uniformly magnetized in the direction of a second arrow 19.
  • a write current applied to the head forms a magnetizing region 20 within which the magnetic field component extends in the direction of a third arrow 21.
  • the magnetizing region 20 is substantially circular as viewed in Fig. 1, typical of a longitudinally oriented, uniaxially anisotropic magnetic recording layer.
  • Different magnetic recording materials afford different f-t-e profiles.
  • Magnetic recording materials useful in the invention include, but are not limited to, iron oxide, cobalt-doped iron oxide, chromium dioxide, barium ferrite, and cobal
  • NRZ recording systems can record binary cells by rapidly reversing the polarity of a substantially constant-magnitude write current, thus creating a transient leading ft e profile 22 and a persistent trailing ft e profile 23 each time the polarity of the write current reverses.
  • the idealized, arcuate, trailing f-t-e profile 23 is identical to each of the previously recorded trailing f-t-e profiles 23a, 23b, 23c, and 23d which separate adjacent oppositely magnetized regions and are similar to the ft e profiles of Figs. 1-3 of the above-cited Fayling II publication.
  • f t e profiles are shown as lines even though they are zones of appreciable width, as can be seen in Figs. 4, 5 and 6 of the above-cited Fayling I publication.
  • trailing f t e profiles are as straight as possible, because this minimizes noise or intersymbol interference in adjacent binary cells upon read-out, thus permitting increased linear bit densities.
  • trailing f t e profiles are less straight than are the idealized f t e profiles shown in FIG. 1 and are more likely to be shaped like those of FIG. 2.
  • FIG. 2 shows trailing f t e profiles 25, 26, 27 and 28 of digital data that was recorded on magnetizable layers having coercivities of 317, 597, 740, and 816 Oe, respectively. Those four magnetizable layers are collectively indicated as magnetizable layer 12a. Because of idiosyncrasies of the magnetizable particles of those layers, none of the trailing f t e profiles 25, 26, 27 and 28 is approximately straight or extends approximately perpendicular to the surface 24 of the magnetizable layer 12a.
  • Portions 25a and 26a of the trailing ft e profiles 25 and 26, respectively, are dotted to meet the following conditions: (a) the dotted portion 25a extends to the same depth into the magnetizable layer 12a as the dotted portion 26a begins and (b) the centers of dotted portions 25a and 26a lie on an imaginary line (not shown) that is perpendicular to the surface 24 of the magnetizable layer.
  • the NRZ binary magnetic recording system of FIG. 3 is identical to that of FIG. 1 except that its magnetic recording medium 30 has a nonmagnetizable backing 32 bearing two coextensive, contiguous magnetizable layers.
  • the coercivity of the outer layer 33 is 317 Oe, and that of the inner layer 34 is 597 Oe, the coercivities that provided the FIG. 2 trailing f t e profiles 25 and 26, respectively.
  • the thickness of the outer layer 33 has been selected to equal the depth to which the dotted portion 25a penetrates into the magnetizable layer in FIG. 2.
  • the thickness of the inner layer 34 has been selected to equal the region of the magnetizable layer occupied in FIG. 2 by the dotted portion 26a.
  • the dotted portions 25a and 26a together indicate the trailing ft e profile that separates adjacent binary cells recorded on the magnetic recording medium 30.
  • trailing f t e profile is a jagged composite, it is straighter than are either of the trailing f t e profiles 25 and 26, and it is closer to being perpendicular to the surface of the magnetizable layer 33 than are either of the trailing ft e profiles 25 and 26.
  • portions 27a and 28a of the trailing f t e profiles 27 and 28, respectively, are dotted to meet the following conditions: (a) the dotted portion 27a begins at the same depth into the magnetizable layer 12a as the dotted portion 25a extends, and the dotted portion 27a extends to the same depth as the dotted portion 28a begins and (b) the centers of dotted portions 27a and 28a lie on an imaginary line (not shown) that is perpendicular to the surface of the magnetizable layer.
  • the NRZ binary magnetic recording system of FIG. 4 is identical to that of FIG. 1 except that its magnetic recording medium 40 has a nonmagnetizable backing 42 bearing three coextensive, contiguous magnetizable layers.
  • the coercivity of the outer layer 43 is 317 Oe
  • that of the first inner layer 44 is 740 Oe
  • that of the innermost layer 45 is 816 Oe.
  • the thickness of the outer layer 43 is identical to that of the outer layer 33 of FIG. 3, and the thicknesses of the inner layers 44 and 45 have been selected to equal the depths of the dotted portions 27a and 28a, respectively in the magnetizable layer in FIG. 2.
  • FIG. 1 The coercivity of the outer layer 43 is 317 Oe
  • that of the first inner layer 44 is 740 Oe
  • that of the innermost layer 45 is 816 Oe.
  • the thickness of the outer layer 43 is identical to that of the outer layer 33 of FIG. 3, and the thicknesses of the inner layers 44 and 45 have been selected to equal
  • the dotted portions 25a, 27a, and 28a together indicate the trailing ft e profile that separates binary cells recorded on the magnetic recording medium 40.
  • trailing f t e profile is a jagged composite, it is straighter than are each of the trailing ft e profiles 25, 27 and 28 of FIG. 2, and it is closer to being perpendicular to the surface of the magnetizable layer 33 than are any of the trailing ft e profiles 25, 27 and 28.
  • the head-to-medium spacing 18 is the same.
  • different recording devices require different head-to-medium spacings.
  • Even in contact recording there is an effective head-to-medium spacing due to irregularities in the surface of the magnetic recording medium.
  • a specific recording device might require a head-to-medium spacing equal to the distance between the pole tips 14,15 and the magnetizable layer 44 of FIG. 4.
  • a suitable magnetic recording medium could be identical to the medium 40 of FIG. 4 except omitting the outer layer 43.
  • the ability to achieve straighter trailing f t e profiles arises from the phenomenon discussed above in connection with Fayling III and verified in FIG. 2.
  • the innermost magnetizable layer can have lower coercivity than central magnetizable layer for reasons comparable to those disclosed in the above-cited Perrington patents, and the presence of an inner magnetizable layer of lower coercivity does not necessarily detract from the straightness of the trailing f t e profile.
  • the coercivity (He) of each inner layer of the magnetic recording medium of the invention preferably does not exceed that of any outer layer by more than 25%.

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Abstract

Support magnétique d'enregistrement pour données binaires à hautes densités linéaires de bits comportant au moins deux couches magnétisables coextensives contiguës de coercitivité (HC) différente choisies pour que lors de l'enregistrement de données binaires les profils arrière du bord de transition de flux séparant les cellules binaires contiguës soient plus droits et plus voisins de la perpendiculaire à la surface magnétisable du support que celui des profils arrière du bord de transition de flux de chacune des couches magnétisable prise isolément. La coercitivité de la couche extérieure est normalement moindre d'au moins un facteur 2 que celle de la couche intérieure contiguë. La couche extérieure doit être suffisamment mince pour réduire au minimum l'espace compris entre la couche de tête et la couche intérieure, et la coercitivité de la couche extérieure suffisamment élevée pour assurer la stabilité de l'enregistrement de préférence entre 500 et 2000 Oe.
PCT/US1995/004962 1994-06-17 1995-04-24 Support multicouches d'enregistrement magnetique pour enregistrements a hautes densites lineaires de bits WO1995035566A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US26171794A 1994-06-17 1994-06-17
US08/261,717 1994-06-17

Publications (1)

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WO1995035566A1 true WO1995035566A1 (fr) 1995-12-28

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0454139A2 (fr) * 1990-04-26 1991-10-30 Fuji Photo Film Co., Ltd. Milieu d'enregistrement magnétique et procédé pour sa fabrication
DE4142052A1 (de) * 1990-12-20 1992-07-02 Fuji Photo Film Co Ltd Magnetaufzeichnungsmedium

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0454139A2 (fr) * 1990-04-26 1991-10-30 Fuji Photo Film Co., Ltd. Milieu d'enregistrement magnétique et procédé pour sa fabrication
DE4142052A1 (de) * 1990-12-20 1992-07-02 Fuji Photo Film Co Ltd Magnetaufzeichnungsmedium

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