U.S. patent number 3,639,699 [Application Number 05/014,945] was granted by the patent office on 1972-02-01 for magnetic transducer having a composite magnetic core structure.
This patent grant is currently assigned to General Electric Company. Invention is credited to Jerome J. Tiemann.
United States Patent |
3,639,699 |
Tiemann |
February 1, 1972 |
MAGNETIC TRANSDUCER HAVING A COMPOSITE MAGNETIC CORE STRUCTURE
Abstract
A magnetic transducer for read-write applications is disclosed
in which a composite core having two closely spaced legs is
provided with each leg having one layer of magnetic material of
higher permeability and lower saturation flux density than the
second layer of that leg. The read-write conductor means is
positioned between the two legs and is thereby inductively coupled
to the core. The higher permeability layer is narrow in a direction
perpendicular to both the length of the leg and the thickness of
the layer, is adjacent the conductor means and is saturated at flux
densities encountered in writing so that the wider lower
permeability outer layers of the two legs are effective during
writing and the higher permeability narrower layers are effective
or dominant during reading. In a modification, a composite shim is
employed in the gap of a more conventional stacked lamination head
to obtain some of the advantages of the present invention.
Inventors: |
Tiemann; Jerome J.
(Schenectady, NY) |
Assignee: |
General Electric Company
(N/A)
|
Family
ID: |
21768704 |
Appl.
No.: |
05/014,945 |
Filed: |
February 27, 1970 |
Current U.S.
Class: |
360/125.33;
G9B/5.089; G9B/5.086; G9B/5.064 |
Current CPC
Class: |
G11B
5/2452 (20130101); G11B 5/3143 (20130101); G11B
5/313 (20130101) |
Current International
Class: |
G11B
5/245 (20060101); G11B 5/31 (20060101); G11b
005/22 () |
Field of
Search: |
;179/1.2C ;340/174.1F
;346/74MC |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Fears; Terrell W.
Assistant Examiner: Tupper; Robert S.
Claims
What I claim as new and desire to secure by Letters Patent of the
United States is:
1. A read-write head comprising a magnetic core having a pair of
legs in series magnetic relation, read-write conductor means
inductively coupled to said legs and passing therebetween, each leg
comprising two superimposed layers, each of a different magnetic
material, the magnetic material of the layers closest to said
conductor means have a substantially higher permeability and lower
saturation flux density than the other layers.
2. The read-write head of claim 1 wherein said one layer is
physically narrower in a direction perpendicular both to the
thickness of the layer and to the length of the leg of which it is
a part than the other layer.
3. The read-write head of claim 1 wherein said one layer saturates
at flux densities therein during writing so that the other layer of
each leg provides the dominant magnetic circuit during writing.
4. A read-write head comprising a magnetic core having a pair of
legs in series magnetic relation, read-write conductor means
inductively coupled to said core and passing between the legs
thereof, each leg comprising two superimposed layers, each of
magnetic material having different initial permeability, the layers
having higher permeability being adjacent said read-write conductor
means so that the last-mentioned layers dominate the magnetic
characteristics of said head during the read operation.
5. The read-write head of claim 4 where the axis of easy
magnetization of the layers adjacent said conductor being parallel
to the width of said layers and the axis of easy magnetization of
the other two layers being parallel to the length of said layers.
core.
6. The read-write head of claim 4 wherein the width of the magnetic
layers adjacent the read-write conductor means is narrower than the
other of said layers.
7. A read-write head comprising a magnetic core having a stack of
laminations of magnetic material terminating in spaced opposed pole
faces defining a gap and a composite shim including a layer of
magnetic material adjacent each pole face having a substantially
higher permeability and lower saturation flux density than the
magnetic material of said core and a layer of nonmagnetic material
interposed between said layers of magnetic material, said composite
shim having a lesser width dimension than that of the stack of
laminations of said core for providing a narrower effective head
during reading than during writing and read-write conductor means
inductively coupled to said core.
Description
The present invention relates to an improved transducer and
particularly to an improved magnetic read-write head having
improved operating characteristics for the read-write
functions.
The requirements for high quality operation of a magnetic head for
the writing function are substantially different from those
required during the reading function. Accordingly, it has been
difficult to provide a single structure with entirely satisfactory
characteristics for both functions. Some attempts have been made to
improve the compromise in the characteristics of read-write heads
and in some cases separate heads have been employed for the two
functions even though this has resulted in more expensive and more
complex systems.
Accordingly, it is an important object of the present invention to
provide an improved magnetic transducer for both reading and
writing functions which provides for deep penetration of the
recording medium by the magnetic field in writing as well as good
resolution and high sensitivity in reading.
While not limited thereto, the invention is particularly applicable
to deposited film-type transducers and makes use of at least two
layers of magnetic material in each leg of the magnetic circuit of
the transducer with the materials having different characteristics
and, in the preferred embodiment, having different compositions.
The present invention also provides for a head whose read-write gap
is effectively wider for the writing function than it is for the
reading function in a direction perpendicular to the direction of
relative movement between the head and recording medium and the
length of the magnetic circuit and whose read-write gap is
effectively wider in the direction parallel to the relative
movement between the recording medium and the magnetic head for the
writing function as compared to the effective gap width for the
reading function. These characteristics result from the magnetic
properties of the material employed in the different layers and the
orientation of their magnetic anisotropy with respect to the
read-write gap and the conductive means associated with them. These
properties and orientations are chosen so that the different
magnetic states that exist during writing and reading automatically
produces the changes in effective length and width of the
read-write gap.
Further objects and advantages of my invention will become apparent
as the following description proceeds, reference being had to the
accompanying drawing and its scope will be pointed out in the
appended claims.
IN THE DRAWING
FIG. 1 is an isometric view of a deposited film-type of read-write
head embodying the present invention;
FIG. 2 is a sectional view along the line 2--2 of FIG. 1;
FIG. 3 illustrates a modification of the invention as applied to a
more conventional stacked lamination-type of read-write head;
and
FIG. 4 is an enlarged sectional view of the read-write gap of the
head of FIG. 3.
In FIGS. 1 and 2 of the drawing, the present invention is shown
embodied in a deposited film-type of transducer in which the
multiple layer structure providing the magnetic circuit and
associated inductively coupled conductor means is produced by the
deposition of successive layers on a substrate 10 of suitable
material, such as silicon, which provides a support for the head
assembly as well as a heat sink for absorbing heat generated in the
device. Certain ceramics such as beryllia and alumina may also be
employed as the substrate material. As is well understood, the
deposited film technique is particularly suited to the production
of an array of small and closely spaced transducer assemblies and
the structure described in connection with FIG. 1 may be one of a
series of such structures positioned in side-by-side relation on
the substrate 10.
As illustrated in the drawing, the structure is made up of
successive layers of material deposited on the substrate 10 and
upon one another. The first layer 11 is magnetic material such as a
cobalt-iron alloy. The second layer 12 is also of magnetic material
and is narrower in width than layer 11 and is of a suitable alloy
such as nickel-iron. This second layer has a higher initial
permeability and lower saturation flux density than the first layer
or lamination 11. Next is a layer 13 of insulating material such as
silicon dioxide and then a conductor 14 such as copper or gold
having one edge thereof connected with what may be considered a bus
15 which interconnects one terminal of the conductor of each of a
plurality of magnetic heads which, as mentioned, may be located
side-by-side on substrate 10. The other terminal of the conductor
14 is provided by the portion 16 which is individual to each
device. The device is completed by successive layers in the reverse
order including an insulating layer 17 of silicon dioxide, the
layer 18 of relatively high permeability low-saturation flux
density magnetic material such as nickel-iron and finally the outer
layer of magnetic material 19 of lower permeability higher
saturation flux density material. As will be readily understood by
those skilled in the art, the head operates in very closely spaced
relation with a disk or, as illustrated, a tape 20 providing the
magnetic recording medium, and the relative movement between the
medium and the head during reading or writing is in a vertical
direction as viewed in FIGS. 1 and 2 and as indicated by the arrow
in FIG. 1.
As indicated earlier, the head is preferably formed as a deposited
film device and methods for making such deposited films are well
developed in the art and include evaporation, electroplating and
sputtering. Sputtering is the preferred method since the deposition
of a sputtered layer of predetermined composition is much more
easily obtained an controlled than it is in evaporation, for
example.
As an example of specific materials and method of fabricating a
device embodying the present invention, a substrate of silicon of
suitable dimensions for an array of magnetic heads in side-by-side
relation, perhaps 200 or so, is placed in a suitable vacuumtight
enclosure or bell jar for carrying out the sputtering process and
the layers are then applied and photoengraved to the required
pattern in succession as will be readily understood. The first
layer 11 of magnetic material may have a width on the order of 10
mils and a thickness of 1 microns and a composition of pure cobalt,
pure iron, or alloys thereof with up to 20 percent of either the
cobalt or the iron. A preferred composition for providing the lower
permeability, high-saturation flux density characteristics desired
for the two outer or write layers 11 and 19 is 95 percent cobalt, 5
percent iron. The next layer or lamination 12 is of iron-nickel and
has a composition such that the permeability is much higher and the
saturation flux density much lower than those same parameters of
the cobalt-iron layer 11 and is physically narrower than layers 11
and 19, preferably about 80 percent of the width or 8 -mils-wide.
The desired characteristics are readily obtained with a composition
of 85 percent nickel and 15 percent iron, for example. Next, a
layer of silicon dioxide is sputtered over the laminations in an
area near the free edge thereof to provide insulation between the
laminations and the conductive layer 14. This layer is preferably
as thin as possible consistent with providing adequate electrical
insulation between the magnetic layer and the conducting layer and
may be approximately 1,000 A. thick. The gold or copper conductor
is then deposited over the insulating layer and over the two
magnetic layers 11 and 12 near the edge of the substrate and
extending over the substrate to provide the conductor and terminal
areas 15 and 16. The desired configuration can be obtained by
electroplating through holes in an insulating film which are of the
desired shape, or since the previously deposited metal films are
now covered by the insulating film, photoetching can also be used
to define this member. The conductor may be rather thin and in the
particular example being described is 3 -to 5 -microns-thick. Steps
similar to these are then carried out to establish the second
insulating layer of silicon dioxide 17, the nickel-iron layer 18
and the cobalt-iron layer 19. If desired, a thin-sputtered layer of
chromium may be provided over the substrate and/or both sides of
the silicon dioxide layers to promote adherence of the films.
As will be readily understood, the construction just described
provides a magnetic circuit terminating in pole pieces at the edge
of the substrate which are spaced apart with each leg of the
magnetic circuit provided with two layers of magnetic material with
different characteristics, and in the example just described of
different compositions. Also, the conductor is near the free ends
of the spaced leg portions of the magnetic circuit and is
inductively coupled to the magnetic structure to provide means for
the writing input to the magnetic head or the reading output
connection to the magnetic head by way of the common terminal 15
and individual terminal 16 and the associated read and write
circuitry. It will be understood that the edge of assembly may be
machined or ground to a smooth surface, which coincides with the
aerodynamic surface of a flying head shoe, to provide a recording
gap or a reading gap. The flux passing across the gap passes
through the adjacent material of the recording medium to magnetize
the recording medium during the write operation or to sense the
magnetic state of the recording medium in the read operation.
It is an important feature of the present invention that the width
of the head be greater for writing in a direction perpendicular
both to the direction of relative movement between the magnetic
head and the recording medium and to the length of the magnetic
circuit of the head as compared with the effective width during the
reading operation. This is accomplished in the embodiment
illustrated by the magnetic properties and the relative widths of
the two layers of each leg. At the relatively low flux density
encountered during the read operation, the narrower laminations 12
and 18 of relatively high permeability are unsaturated and dominate
in the magnetic circuit associated with the conductor 14. During
the write operation, much higher flux densities are encountered and
said inner layers are saturated. The characteristics of the head
during writing are therefore determined by the lower permeability
high-saturation flux density material of the outer or write
laminations or layers of magnetic material 11 and 19. It will be
noted that by having the read magnet circuit provided by the layers
12 and 18 adjacent the conductor that the gap is much shorter in
the direction of relative movement between the head and the medium
for read than it is for the write operation and by making the width
of the inner layers less than the outer layers, which are effective
during writing, that a narrower width of the recording material is
sensed during reading than the width of the track in writing. By
providing a narrower gap associated with the read circuit,
sensitivity to short wavelength signals is improved and by
providing a narrower track during reading, the edge or marginal
portions of the recorded track are eliminated. Since the edge
portion of the track is not recorded with good fidelity, and since
spurious signals may be found in these regions, the fidelity of the
read back is improved.
While particular materials have been described above, it is
apparent that the advantages of the present invention may be
obtained with any combination of materials in which the layer
adjacent the conductor means has a relatively high permeability and
low-saturation flux density compared to the material on the outer
layer. It is possible to obtain much of the advantage of the
present invention by providing the layer adjacent the conductor
means with a much higher permeability than the outer layer, even
though the saturation flux density may be the same. This may be
accomplished in a simple manner by using the same composition for
all of the magnetic layers and making use of the large difference
in permeability produced by shifting the axis of easy magnetization
by 90.degree. in the inner layers as compared with the outer
layers. As is well understood by those skilled in the art, this
axis of easy magnetization is determined by the direction of the
magnetic field applied during the deposition of the film layers and
the axis of easy magnetization is in the direction of such applied
magnetic field. The axis of easy magnetization is shown by the
arrows on the inner and outer layers of magnetic material in FIGS.
1 and 2 of the drawing. For such an embodiment utilizing a single
material, nickel-iron alloy is particularly well-suited and the
permeability may be changed by a factor of 100 in this manner for
an alloy of 60 percent nickel, 40 percent iron. Satisfactory
results are readily obtained with nickel ranging from 50 percent to
80 percent and iron ranging from 50 percent to 20 percent. It will
be understood that the affect of the direction of the easy axis of
the magnetization will be used in the embodiment of the invention
utilizing different compositions in the inner and outer magnetic
films to enhance the difference in the magnitudes of the
permeabilities of the inner and outer layers.
In FIG. 3 I have shown a further modification embodying features of
my invention in which by a suitable composite shim certain
advantages of my invention are obtained with a more conventional
type of laminated head structure. As shown in FIG. 3, the head may
include a stack of laminations 21 of generally "C" shape
terminating with opposed faces 22 and 23 across which the flux
extends and couples with the recording medium. A read-write coil 24
is inductively coupled to the core.
A composite shim 25 which fills the entire gap or space between the
pole pieces may be made up of two layers 26 and 27 adjacent the
pole pieces 22 and 23 of high-permeability, low-saturation flux
density magnetic material such as a nickel-iron alloy, described
above, separated by a layer 28 of nonmagnetic material, such as
copper. Preferably, the high-permeability material is of a lesser
dimension in a direction into the paper as shown in FIG. 3 than the
other laminations at the pole faces 22 and 23 so that the width of
the shim adjacent the magnetic material of the core is less than
the width of the laminations, thus giving a narrower effective head
during reading than the effective width of the head during writing.
It will be apparent that with this construction, the
high-permeability material is not saturated during the read
operation and sensitivity as well as good resolution are provided
because of the narrowed width for reading as well as the relatively
narrow gap during reading. During write, the high-permeability
material is saturated and the effective gap as well as width of the
head for writing is greater, being determined by the laminations of
the head.
Thus, it will be seen that by this relatively simple modification
of what may be considered a somewhat conventional laminated
construction of a read-write head that improved operating
characteristics for the combined functions of reading and writing
are obtained.
* * * * *