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
  • G11B5/127—Structure or manufacture of heads, e.g. inductive
  • G11B5/187—Structure or manufacture of the surface of the head in physical contact with, or immediately adjacent to the recording medium; Pole pieces; Gap features
  • G11B5/23—Gap features
• • 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
  • G11B5/127—Structure or manufacture of heads, e.g. inductive
  • G11B5/187—Structure or manufacture of the surface of the head in physical contact with, or immediately adjacent to the recording medium; Pole pieces; Gap features
  • G11B5/1875—"Composite" pole pieces, i.e. poles composed in some parts of magnetic particles and in some other parts of magnetic metal layers
  • G11B5/1877—"Composite" pole pieces, i.e. poles composed in some parts of magnetic particles and in some other parts of magnetic metal layers including at least one magnetic thin film
  • G11B5/1878—"Composite" pole pieces, i.e. poles composed in some parts of magnetic particles and in some other parts of magnetic metal layers including at least one magnetic thin film disposed immediately adjacent to the transducing gap, e.g. "Metal-In-Gap" structure
• • 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
  • G11B5/127—Structure or manufacture of heads, e.g. inductive
  • G11B5/187—Structure or manufacture of the surface of the head in physical contact with, or immediately adjacent to the recording medium; Pole pieces; Gap features
  • G11B5/23—Gap features
  • G11B5/232—Manufacture of gap

Definitions

• This invention relates in general to magnetic heads and to their methods of manufacture. More particularly, though, the invention is directed to magnetic heads which are comprised of gapped ferrite cores.
• FIG. 1 is a diagram useful in describing a prior art problem solved by means of the invention
• Fig. 2 is a side elevation view of a prior art head over which the invention provides improvement
• FIG. 3 is a not-to-scale diagram useful in describing the invention
• Figs. 4-6 illustrate various procedures employed in producing a magnetic head incorporating the invention
• Fig. 7 is a diagram useful in describing the invention.
• OMPI is, in fact, the particular head structure which last coacts with the record zone(s) of the medium, it is widely accepted that the definition of the record zone(s) will be pronounced so long as the record gap trailing edge is sharply defined (i.e. the record zone(s) will be easily discernible during playback) .
• teaching of U.S. Patent No. 4,302,790 has been found to provide not only as good, but better, playback of recorded signals, despite the fact that the depth of recording is only about as great as the length of the record head gap.
• One explanation for this playback improvement is that, with the recording practice of U.S. Patent No. 4,302,790, there is little or no overlapping of (arcuate) record zones which algebraically add to knockdown the playback signal, the record zones being (resolution-wise) extremely narrow and sharp because of the extremely short transducer gap employed to effect recording.
• Ferrites exhibit many properties which are highly desirable in magnetic heads: ferrites are hard and wear well; they have high resistivity and thus tend to inhibit eddy current losses at high recording frequencies; and they have relatively high permeability.
• ferrite saturation magnetization of ferrite material (typically, ferrite saturation occurs at about 4000 gauss) is considerably less than that of other head materials such as ternary alloys of aluminum, iron and silicon (which are often referred to as Sendust; and typically saturate at about 10,000 gauss), ferrite material nonetheless has found wide usage in connection with magnetic recording heads, especially - -
• Fig. 1 is a widely accepted showing of the field strength distribution in the vicinity of the gap of a recording head. Such field strength distribution has been discussed by C. D. Mee, The Physics of Magnetic Recording, Vol. II, 1964, page 40, and by C. B. Pear, Magnetic Recording in Science and Industry, 1967, page 32, the field H identified in Fig. 1 being the field within the depicted record head gap g, and the field H being that at various distances from such head gap.
• a high energy recording medium which the assignee hereof has employed has a typical coercivity of 850 oersteds, a saturation magnetization of 1600 gauss, a permeability of about two, a nominal 90 percent of saturation remanence that occurs for an applied field H of about 1375 oersteds, and a nominal 10 percent of saturation remanence that occurs for an applied field of about 500 oersteds.
• the depth y of recording in a medium when recording as taught in U.S. Patent No. 4,302,790, approximates the lengthwise dimension of the record gap g.
• the depth y within the recording medium at which the aforesaid 1375 oersteds of applied field appears equals the length of the record gap g.
• edge g' to saturate during recording (a problem known as pole tip saturation), whereby the permeability of the edge-defining core material became equal to one, the effective gap would not only enlarge, but its dimensions would become fuzzy, i.e. the recording field gradient would become slight.
• the relationship between core permeability and field gradient has been discussed both by T. Suzuki et al, IEEE Transactions on Magnetics, MAG-8, September 1972, page 536, and by
• FIG. 2 shows a magnetic head comprised of a « 5 ferrite core 10 having a non-magnetic transducer gap 12 defined by Sendust pole pieces 14 bonded at 16 to the ferrite core 10.
• a magnetic head constitutes a compromise at best: relatively high permeability and eddy-current limiting is provided by the ferrite core 10; and high satura ⁇ tion magnetization is provided by the Sendust pole pieces 14 at relatively little sacrifice in overall permeability.
• the general concept of the invention is to coat at least the trailing pole face of a pair of ferrite pole faces, which define a transducer gap, with high-saturation material such as Sendust.
• the long-wearing ferrite will desirably constitute the principal head part that slidingly coacts with a recording medium, (2) the high reluctance glue line will be obviated, and (3) the signal flux will enter the gap region uniformly over the surface of the gap, thereby providing enhanced high frequency efficiency.
• the Sendust coating on the ferrite pole face is produced, prefer ⁇ ably, by sputtering.
• Fig. 3 which is similar to Fig. 1 but shows the existence of (sputtered) coatings 18 of Sendust on both ferrite pole parts 20.
• the coatings are between about 0.25 and 2.0 microns thick, the showing of Fig. 3 being clearly not to scale. Notwithstanding this intentional mis-showing (for ease of comparison with Fig.
• a ferrite head embodying the invention In making a ferrite head embodying the invention (see Figs. 4, 5), the prior art practices of forming a rectangularly shaped ferrite half-bar, chamfering it to form a half-window 25, and lapping the chamfered bar to provide a precisely defined pole face part 26 are employed. Rather than deposit high- saturation material directly on the lapped down pole face part 26, however, the invention (preferably) calls for the removal of the Beilby layer that exists as a result of the lapping operation. As is known, cold-working, e.g. lapping, ferrite material has the effect of causing a stress induced permeability change at the surface of the material being worked, such sur- face change constituting a relatively high reluctance (Beilby) layer.
• Beilby relatively high reluctance
• Beilby layer is removed, for example, by ion milling away several microns of the ferrite pole face part prior to the sputtering procedure.
• the chamfered half-bar is then provided with a deposition 30 of Sendust (or the like) .
• a deposition 30 of Sendust (or the like) .
• Such a coating may be produced by a sputtering set-up as depicted in Fig. 6, wherein a target of Sendust is as ⁇ aulted by the ions of a plasma discharge, thereby causing Sendust to sputter onto the milled pole face part 26. Care must be taken that the Sendust target is devoid of an oxide coating since such may cause a "ghost-producing" gap just like the above noted “Beilby-produced” gap.
• Sendust may have lower permeability than the indicated ferrite material, it may be desirable to prevent a coating of Sendust from appearing at the back gap region 34 of the half-bar.
• This precaution a ⁇ ure ⁇ that, when two half-bars are brought together for purposes of forming a structure that is diceable into gapped cores, there won't be any Sendust in the back gaps of such diced cores which would render their overall reluctance higher than would otherwise be.
• a po ⁇ itionable mask 40 is provided as part of the sputtering set-up and, when properly positioned, the mask 40 will limit the deposition of Sendust to the pole tip region of the half-bar being coated.
• a non-magnetic gap spacer material 36 e.g. SiO
• Sendust-coated chamfered half-bar 37 is brought into face-to-face relationship with the first half-bar (39).
• the unitary a ⁇ embly of half- bar ⁇ i ⁇ contoured After bonding, the unitary a ⁇ embly of half- bar ⁇ i ⁇ contoured; and then diced into individual tran ⁇ ducer core ⁇ , each having a Sendust liner in its transducer gap.
• a thin layer locates the vestigal gap in close proximity to the main record gap. Assuming the head in question is, again, to be used for both record and playack, both the main and vestigal gaps will see, depending both on the spacing between such gaps and the wavelength of the recorded signal, essentially the same signal flux. Widely spaced main and ve ⁇ tigal gaps (thick layer) will see the same flux-sense for long wave ⁇ length recorded signal ⁇ , whereas closely spaced main and vestigal gaps (thin layer) will see the same flux-sense for short wavelength recorded signals. Thus, by using an extremely thin pole face layer, any "bumps" that may occur in the reproduce curve by virtue of the coaction of the two gaps in que ⁇ tion will be located well-out in the higher frequency region of such curve. Given the conflicting requirements for layer thickness, it would seem that a layer from somewhere between about 0.25 and 2.0 microns would be a reason ⁇ able compromise for layer thickness.

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• Manufacturing & Machinery (AREA)
• Magnetic Heads (AREA)

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• 1983
  • 1983-02-25 EP EP19830901054 patent/EP0108074A4/de not_active Withdrawn
  • 1983-02-25 WO PCT/US1983/000260 patent/WO1983003918A1/en not_active Application Discontinuation

Patent Citations (8)

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