GB2260846A

GB2260846A - Composite magnetic heads

Info

Publication number: GB2260846A
Application number: GB9214597A
Authority: GB
Inventors: Masanobu Yamazaki; Ryo Goto
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 1991-07-11
Filing date: 1992-07-09
Publication date: 1993-04-28
Anticipated expiration: 2012-07-09
Also published as: GB9214597D0; GB2260846B

Abstract

A flying type composite magnetic head 41 having an improved playback output power and over-write characteristics is provided by fabricating the magnetic head core thereof in a specified manner. The composite magnetic head 31 comprises a pair of single crystal Mn-Zn ferrite cores 32, 32' having arranged in such a manner to face each other, a thin magnetic film 33 of a metal and a magnetic gap being formed on at least one of said cores on the surface facing the other core, and a narrow track the track width of which is defined by a cutting, wherein, the track width Tw and the core width Cw are each defined to be in the range of 3 mu m </= Tw </= 10 mu m and (5 - 8) x Tw mu m </= Cw </= 130 mu m. <IMAGE>

Description

COMPOSITE MAGNETIC HEADS The present invention relates to a composite magnetic head core and a flying-type composite magnetic head of a composite type ( hereinafter referred to simply as "a composite flying-type magnetic head") using the same, which are used in compact magnetic disk apparatuses. More particularly, the present invention relates to a composite magnetic head core comprising a pair of cores made of single crystal Mn-Zn ferrite, provided that at least one of said pair of cores has on the surface facing the other a magnetic thin film of a metal. The present invention also relates to a composite flying-type magnetic head using said core, which is used particularly in compact magnetic disk apparatuses for high frequency and high density recording, in for example, 3.5inch and 2.5-inch disks.

FIG. 3 and FIG. 4 are respectively a perspective view of a magnetic head core and a composite flying-type magnetic head, for use in a compact magnetic disk apparatus capable of high frequency and high density recording.

Referring to FIG. 3, the structure of a composite magnetic core is described. The magnetic head core 31 comprises a pair of single crystal Mn-Zn ferrite core pieces 32 and 32' having high permeability, and one of the core pieces z USisprc##th a magnetic thin film 33 of a metal having high saturation flux density deposited on the surface opposing the other core piece. The pair of core pieces are bonded together with a nonmagnetic material 34 to establish a magnetic gap, and this bonding is further reinforced with a glass bonding 35.

In FIG. 4, a flying-type magnetic head 41 comprises a slider 42 fabricated with a non-magnetic material such as CaTiO3, and the magnetic head core 43 is fixed with a mold glass 45 inside a slit 44 provided in an air bearing 46.

With the recent demands for more compact and higher density recording magnetic disk apparatuses, developments are made on increasing line recording density and track recording density. Accordingly, the magnetic gap length of a magnetic head is reduced to cope with a higher line recording density.

On the other hand, to meet the demand for a higher track recording density, as shown in Fig.3 , a cutting is provided on the magnetic head core having a core width of Cw to confine the track width to Tw.

For example, a magnetic head having a core width Cw of 152 g m and a track width Tw of 13.5g m is disclosed in JP-A-63 -293710 (the term "JP-A-" as used herein signifies "an unexamined published Japanese patent application"), and magnetic heads having specified core widths Cw of 178 g m and 152 R m and a track width Tw of 13.5 g m are disclosed in JP-A -2- 263302.

The planar recording density of a magnetic disk has increased from 60 megabit/inch2 to 100 megabit/ inch2 , and a perspective tells that it further increases to a range of from 200 to 250 megabit/inch2. The present inventors have confirmed through their study that a composite magnetic head comprising a single crystal Mn-Zn ferrite and a thin magnetic film of a metal favorably corresponds to a high density recording of 250 megabit/inch2, an area conventionally believed left for thin film magnetic films.A magnetic head having a reversal magnetization density of around 25,000 FCI, a track recording density of about 2,400 TPI, and a linear recording density of about 33,000 BPI is required to realize a planar recording density of about 100 megabit/inch2; to further achieve a higher planar recording density in the range of from 200 to 250 megabit/inch2, a reversal magnetization density in the range of from 50,000 to 57,000 FCI, a track recording density of from 3,000 to 3,300 TPI, and a linear recording density of from 67,000 to 76,000 BPI is necessary.To realize such a high density recording, the magnetic head must have a track width controlled to 10 ss m or less, and, particularly in a higher density recording in the range of from 200 to 250 megabit/inch2, the track must be further narrowed to a range of from 3 to 8 g m .Similarly, the length of the magnetic gap should be 0.5 a m or less, preferably, about 0.3 ce m Because a composite flying-type magnetic head comprises a non-magnetic slider having fitted therein a magnetic head core in which a magnetic circuit is established by a pair of single crystal Mn-Zn ferrite cores having a high-permeability non-magnetic slider and a thin film of a metal having a high saturation flux density, it has a smaller inductance than a monolithic magnetic head made wholly from polycrystalline Mn-Zn ferrite. However, with increasing frequency for higher density recording, a low inductance which had been ignored previously has been noticed problematic, because it impairs the magnetic head characteristics by increasing the noise level. This is due to the resonance of the inductance with the frequency at playback.

The playback output tends to decrease with reducing track width. This tendency becomes particularly pronounced with a track width of 10 R m or less, and a distinct drop in the overwrite characteristics occurs at the outer peripheral portions.

However, if the core width were to be excessively narrowed, a magnetic field intensity sufficiently strong for the playback at the magnetic gap would not be obtained. If the core width were to be increased in excess, on the other hand, a too high inductance results, thereby increasing the noise.

An object of the present invention is to overcome the problems mentioned hereinbefore, and to provide a magnetic head core for use in a compact magnetic disk suitable for high density recording capable of providing a planar recording density in the range of 250 megabit/inch2. A further object of the present invention is to provide a composite flying-type magnetic head.

The present invention provides a magnetic head core comprising a pair of single crystal Mn-Zn ferrite cores arranged to face each other, a thin magnetic film of a metal and a magnetic gap being formed on at least one of said cores on the surface facing the other core, and a narrow track the track width of which is defined by a cutting, wherein, the track width Tw is defined to be 3 g m or larger but not larger than 10 a m , and the core width Cw is defined to be (5-8) times Tw or larger but not larger than 130 LI m more preferably, the core width Cw is defined in the range of from (5 - 8) times Tw to 100 m . The present invention also provides a composite flying-type magnetic head comprising the magnetic head above buried and fixed in the slit of a non- magnetic slider.

The composite flying-type magnetic head according to the present invention provides a favorable playback output and over-write characteristics because it is equipped with a magnetic head core, the track width Tw and the core width Cw each being confined to a favorable range of from 3 to 10 ss m and from (5 - 8) times Tw to 130 ss m , respectively; the range for Cw more preferably is in the range of from (5 - 8)times Tw to 100 m .

A Tw in the range of from 3 to 10 ss m is preferred in the present invention. In order to achieve a maximum track recording density of ca. 3,300 TPI, a magnetic core with Tw of 10 g m or more cannot follow the high track recording density.

On the contrary, decreasing Tw below 3 a m is no more effective and reversely decreases the yield and efficiency of the cutting process.

A Cw in the range of from (5 - 8)times Tw to 130 ce m is preferred in the present invention. If the Tw were to become 130 g m or larger in a maximum linear recording density of about 76,000 BPI , the inductance becomes too high and hence the core generates too much noise in the desired frequency region.

If the Tw were to become too small as to fall in the range of (5- 8)times the Tw ((5- 8)x Tw) ce m or less, the output becomes excessively low. When the track width is low, in particular, the core width Cw is preferably controlled to 100 LL m or less.

The single crystal Mn-Zn ferrite to be used in the present invention preferably is such a ferrite containing from 26 to 32 mol% MnO, from 14 to 21 mol% ZnO, and balance substantially Fe203 . The magnetic thin film of a metal used in the present invention preferably is an Fe-Al-Si system magnetic film called Sendust, which contains from 2 to 10 % by weight Al, from 3 to 16 % by weight Si, and balance substantially Fe. To obtain a thin film with particularly high permeability, preferred is such containing from 4 to 8 % by weight Al, from 6 to 11 % Si, and balance substantially Fe.

In the accompanying drawings: FIG. 1 is a diagram showing suitable ranges for a track width Tw and a core width Cw for a magnetic head core according to the present invention; FIG. 2 shows schematically a track portion of the composite magnetic head core according to the present invention; FIG. 3 is a perspective view of a composite magnetic head core; and FIG. 4 is a perspective view of a composite flying magnetic head having fixed therein a composite magnetic head core.

FIG. 5 is a diagram showing a relation between a core width Cw and a playback sensitive coefficient a FIG. 6 is a diagram showing a relation between Cw/ Tw and a playback sensitive coefficient a The present invention is explained in further detail below, by way of the following non-limiting examples.

EXAMPLE A 1 X m thick metallic thin film 23 of an Fe-Al-Si system alloy was deposited by magnetron sputtering on a planar single crystal Mn-Zn ferrite substrate 20a, on the surface thereof facing the magnetic gap. The film deposition using sputtering was conducted using a 76 mm diameter and 2 mm thick alloy target containing Fe, Al, and Si, at an RF power of 350 W, at an actual vacuum degree of 5 x 10-4 Pa and a gas pressure of 7 x 10-1 Pa, while maintaining the substrate at 300 C and at a distance of 70 mm from the target.

Separately, SiO2 film was deposited by sputtering on the surface on another single crystal Mn-Zn substrate 20b having an angular-shaped cross section, on the surface on which the magnetic gap 24 is to be formed. The two substrates thus obtained were melt-adhered together by using a PbO-SiO2-B2O3-Na2O system glass at 700 C . The resulting integr ated substrates were cut and lapped to establish a track portion 22, by cutting and thereby defining the track width. Thus was obtained a composite magnetic head core 21 as shown in Fig.2(a).

The magnetic head core 21 was then mounted on a non-magnetic slider, by fitting it into a slit 44 and fixing it with a PbO-SiO2-A12O3-B2O3 system mold glass at 530 C . A composite flying-type magnetic head having mounted thereon a composite magnetic head core as shown in FIG. 4 was then obtained by finishing the surface facing the recording media of the composite-type magnetic head above. As shown in FIG. 2(b), the magnetic head core according to the present example comprises a track portion 22 on one side of the core, but the track portion may be provided in the center of the core as shown in FIG. 2(c), core portion 22'.

FIG. 1 is a diagram showing suitable ranges for a track width Tw and a core width Cw for a magnetic head core according to the present invention. According to this defined range, Tw was maintained constant at 10 R m , while varying the core width Cw alone in three levels of 125, 100, and 75 M m . Separately, a sample having a core width of 150 g m was prepared for comparison. The magnetic heads, 4 sample pieces in total, were subjected to measurements of the head characteristics and the results were studied. The magnetic depth Gd, the gap length G1, and the core height were maintained the same for all the heads, i.e., at 3 ss m , 0.35 LI m , and 610 a m , respectively.

The single crystal Mn-Zn ferrite used contained 27 mol% MnO, 18 mol% ZnO, and balance substantially Foe2 03, and had a permeability in the range of from 1,100 to 1,300 (at 1 MHz) and from 500 to 700 (at 5 MHz), and a saturation magnetic flux density Blo of 5,000 G.

The magnetic thin film contained 85 % by weight Fe, 6% by weight Al, and 9 % by weight Si. This metallic thin film had a permeability along the hard axis direction of 2,100 (at 1 MHz) and 1,700 (at 5 MHz), and a saturation magnetic flux density Blo of 10,500 G.

( EXAMPLE1) The four flying-type magnetic heads using the magnetic head cores varied in core width were subjected to measurements for head characteristics. The measurements were conducted under the following conditions: Coercive force of the magnetic disk : 1,450 Oe Peripheral speed of the disk : 7.64 m/s Flying height of the magnetic head: 0.135 ;z m Measuring current: 25 mAo-p Measuring frequency: 4.5/1.13 MHz Number of turns: 40 turns The results thus obtained are given in Table 1.

Table 1

Sample No. 1 2 3 4 Tw (LI m ) 10 10 10 10 Cw (g m ) 150 125 100 75 Cw/Tw 15 12.5 10 7.5 L ( IL H ) 2.89 2.77 2.57 2.22 HF E (mvp-p) 0.221 0.222 0.224 0.226 Res (%) 87 90 87 85 O/W (-dB) 28.9 29.3 29.3 30.1 E/A (mvp-p/ g H ) 0.130 0.135 0.140 0.152 Legend: L: Inductance; E: Output; A: Square Root of L; Res.: Resolution; O/W: Over-write characteristics; No. 1 is a comparative sample, and Nos. 2 to 4 are the samples of the present invention.

Table 1 clearly shows that the magnetic head samples in accordance with the present invention have a lower inductance, favorable over-write characteristics, and a higher magnetic head efficiency (E/A) as compared with those of the comparative sample. Thus, the present invention provides superior magnetic heads.

It can be seen from the foregoing examples that the present invention provides a composite magnetic head core and a composite flying-type magnetic head using the same, which reduce noise and provide favorable over-write characteristics even in a high density recording of about 250 megabit/inch2, by confining the track width Tw and the core width Cw each to a pertinent range.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

(EXAMPLE2) The flying-type magnetic head using the magnetic head cores varied in core width and track width Tw were subjected to measurements of playback sensitive coefficient a The results thus obtained are shown as Fig.5 . The playback sensitive coefficient a is written as l/(l+Rc/Rg) Rc ; Magnetic resistance of core Rg ; Magnetic resistance of gap portion Rc is written as lc / (Ac R e) , and R6 is Written as G, /(A6 ss cr lc ; Magnetic road length Ac ; Sectional area of magnetic road length a e ; Practical magnetic permeability of core G, ; Gap length Sectional area of gap Xlo; Magnetic permeability of vacuum Fig.5 shows that if the core width Cw were to be narrowed, the playback sensitive coefficient would be decreased.

Then, the flying-type magnetic head using the magnetic head cores varied in Cw/Tw were subjected to measurements of playback sensitive coefficient a . The results thus obtained are shown in Fig. 6 . Fig.6 shows that if Cw/Tw is smaller than (5- 8) , playback sensitive coefficient a is decreased Therefore,it is desirable that Cw/Tw is more than (5 -8).

Claims

CLAIMS:

1. A composite magnetic head core which comprises a pair of single crystal Mn-Zn ferrite cores arranged in such a manner as to face each other, a thin magnetic film of a metal and a magnetic gap being formed between the opposed faces of the cores, and a narrow track the track width of which is defined by a cutting, wherein, the track width Tw and the core width Cw are each defined to be in the range as follows: 3 LI m I Tw ~ 10 IL m and (5 - 8) x Tw g m C Cw C 130 R m .

2. A magnetic head core as claimed in Claim 1, wherein the core width Cw is defined in the range as follows: (5 - 8)x Tw g m ~ Cw j 100 m .

3. A magnetic head core as claimed in claim 1 or claim 2 wherein said single crystal Mn-Zn ferrite comprises 26 to 32 mol% MnO, 14 to 21 mol% ZnO and balance substantially Fe203.

4. A magnetic head core as claimed in any one of claims 1 to 3 wherein said thin magnetic film is an Fe-Al-Si alloy comprising 2 to 10% by wt. Al, 3 to 16% by wt. Si and balance substantially Fe.

5. A flying-type composite magnetic head of a composite type, which comprises a non-magnetic head slider having buried and fixed in the slit thereof a composite magnetic head core as claimed in any preceding claim.

6. A composite magnetic head substantially as herein described in any of the Examples and/or with reference to any of the accompanying drawings.

Amendments to the claims have been filed as follows LAIMS:

1. A composite magnetic head core which comprises a pair of single crystal Mn-Zn ferrite cores arranged in such a manner as to face each other, a thin magnetic film of a metal and a magnetic gap being formed between the opposed faces of the cores, and a narrow track the track width of which is defined by a cutting, wherein, the track width Tw and the core width Cw are each defined to be in the range as follows: 4 # Tw# # 10 ji m < Cw < 130 lt m 2. A magnetic head core as claimed in Claim 1, wherein the core width Cw is defined in the range as follows: (5 - 8)x Tw ii m # Cw # 100 m.

3. A magnetic head core as claimed in claim 1 or claim 2 wherein said single crystal Mn-Zn ferrite comprises 26 to 32 mol% MnO, 14 to 21 mol% ZnO and balance substantially Fe2O3.