U.S. patent number 3,867,368 [Application Number 05/409,613] was granted by the patent office on 1975-02-18 for read-write magnetic transducer having a composite structure comprising a stack of thin films.
This patent grant is currently assigned to Compagnie Internationale pour l'Informatique. Invention is credited to Jean-Pierre Lazzari.
United States Patent |
3,867,368 |
Lazzari |
February 18, 1975 |
READ-WRITE MAGNETIC TRANSDUCER HAVING A COMPOSITE STRUCTURE
COMPRISING A STACK OF THIN FILMS
Abstract
Each pole-piece of a read-write magnetic transducer having a
geometrical airgap defined by a pair of pole-pieces and wherein
passes a part of a read-write flat winging comprises a first layer
made of magnetically soft material adjacent to the airgap and a
second layer made of magnetically hard material with an intervening
layer of a structure ensuring de-coupling of the magnetizations of
the said soft and hard magnetic material layers.
Inventors: |
Lazzari; Jean-Pierre (Villiers
Saint Frederic, FR) |
Assignee: |
Compagnie Internationale pour
l'Informatique (Louveciennes, FR)
|
Family
ID: |
9106735 |
Appl.
No.: |
05/409,613 |
Filed: |
October 25, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Nov 7, 1972 [FR] |
|
|
72.39317 |
|
Current U.S.
Class: |
360/125.33;
G9B/5.091; G9B/5.064; 360/122 |
Current CPC
Class: |
G11B
5/3153 (20130101); G11B 5/2452 (20130101) |
Current International
Class: |
G11B
5/245 (20060101); G11B 5/31 (20060101); G11b
005/12 (); G11b 005/22 () |
Field of
Search: |
;179/1.2C ;340/174.1F
;346/74MC ;29/603 ;360/122,123,125,126 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Eddleman; Alfred H.
Attorney, Agent or Firm: Kemon, Palmer & Estabrook
Claims
1. A read/write transducer comprising: a pair of magnetic
pole-pieces and read-write conductor means inductively coupled to
said pole-pieces and passing therebetween; each pole-piece
including the superposition of:
a first magnetic layer member close to said conductor means;
a magnetostatically decoupling layer means, over said first
magnetic layer member; and
a second magnetic layer member of substantially lower permeability,
substantially higher saturation flux density and appreciably higher
value
2. A read/write transducer according to claim 1, wherein said
magnetostatically decoupling layer means is comprised of a
non-magnetic
3. A read/write transducer according to claim 1, wherein said
magnetostatically decoupling layer means comprises a stack of thin
films of alternating magnetic materials one of which is of
substantially lower permeability, substantially higher saturation
flux density and appreciably
4. A read/write transducer according to claim 1, wherein said first
magnetic layer member consists of a stack of relatively insulated
thin
5. A read/write transducer according to claim 4, wherein said
second magnetic layer member also consists of a stack of relatively
insulated
6. A read/write transducer according to claim 1, wherein the
material of said first magnetic layer member is an iron-nickel
alloy and the material of said second magnetic layer member is
selected from the group consisting
7. In a read/write magnetic transducer comprising a pair of
magnetic pole-pieces and read-write conductor means inductively
coupled to the pole-pieces and passing therebetween, a composite
pole-piece structure comprising a stack of magnetic material thin
films wherein a first plurality of said films close to the said
conductor means are relatively insulated and of a first magnetic
material, a second plurality of said films over the first plurality
are directly contacting each other and alternate first and second
magnetic materials, and a third plurality of said films are
relatively insulated and of the said second magnetic material over
the second plurality of thin films, and wherein the said second
magnetic material is of substantially lower permeability,
substantially higher saturation flux density and appreciably higher
value
8. In a read/write magnetic transducer comprising a pair of
magnetic pole-pieces and read-write conductor means inductively
coupled to the pole-pieces and passing therebetween, a composite
pole-piece structure comprising a first plurality of relatively
insulated thin film of a first magnetic material close to said
read-write conductor means, a nonmagnetic dielectric material layer
over first plurality of thin films, and a second plurality of
relatively insulated thin films of a second magnetic material over
said dielectric layer, the second magnetic material being of
substantially lower permeability, substantially higher saturation
flux density and appreciably higher value of anisotropy field than
the first magnetic material.
Description
BRIEF SUMMARY OF THE INVENTION
The present invention concerns improvements in or relating to the
read-write magnetic transducers made in layers wherein a flat coil
winding is partially inserted between two magnetic flat pole-pieces
defining a geometrical airgap therebetween. The magnetic circuit of
the pole-pieces carries the field which, for a writing operation,
is generated by the coil winding and during a read-out operation,
said circuit carries the field generated from the magnetization
variations of a record carrier.
In read-out operation, the efficiency of the transducer may be
defined by the ratio of the magnetic flux crossed by the coil
winding to the magnetic flux available at the airgap level: the
reluctance of the magnetic material ought to be in such a condition
as low as possible from the winding to the airgap and, for a fair
definition of the read-out signal, the length of the airgap ought
to be the minimum one.
In write-in operation, on the other hand, the efficiency of the
transducer is related to the ratio of the writing field to the
writing electrical current and of the gradient of the magnetic
field at the airgap level: the magnetic material ought to have a
substantially zero remanent flux density and, on the other hand, a
maximal value saturation flux density, together with a permeability
value well above 50.
These two sets of physical conditions have small compatibility, not
to say they are contradictory. They led the manufacturers to
separately design read-only magnetic transducers and write-only
magnetic transducers.
In view of tentatively obviating such a contradiction, it has been
proposed, for instance in U.S. Pat. No. 3,639,699 issued Feb. 1,
1972 in the name of J.J. TIEMAN, to provide each "leg" or
pole-piece of the magnetic circuit comprised by two layers which
are directly contacting one another and which are of magnetic
materials of different properties: the magnetic material of the
layer closest to the airgap has a substantially higher permeability
and lower saturation flux density than the other layer. This design
however suffers a major drawback. As the magnetic layers are
directly contacting, the magnetization of the inner layer is
blocked by the magnetization of the outer layer so that, in actual
practice, the higher permeability quality of the inner layer is
entirely lost.
It is the object of the invention to provide a magnetic read-write
transducer structure which enables in a very simple way the
efficiency and actuality of this two-layer pole-piece
suggestion.
According to a feature of the invention, this aim is reached by
providing between a magnetically soft inner layer and a
magnetically hard outer layer of a pole-pice, an intervening layer
of such a structure that it provides de-coupling of the
magnztizations of the said two layers.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in full detail with reference to
the accompanying drawings wherein:
FIG. 1 shows an exploded view of a magnetic transducer structure
according to the invention and from which may be plainly derived
any modification within the field and scope of the appended
claims,
FIG. 2 shows a top view of the structure,
FIGS. 3 and 4 show cross-section views along section lines a) and
b) of FIG. 2, and,
FIG. 5 shows a partial cross-section view of enlarged scale, of an
illustrative embodiment of one of the pole-piece of a transducer
made in accordance to the invention.
In the drawings, the relative dimensionings of the layers, and
mainly the thicknesses of said layers are not maintained for the
sake of clarity. For the sake of clarity, too, the actual
deformations of the layers are not indicated in the exploded view
of FIG. 1, Such deformations normally occur during deposition in
vacuo of the successive layers of the structure, according to a
well known technique.
DETAILED DESCRIPTION
Referring to FIG. 1, a layer 2 of a magnetic material of high
saturation induction and high saturation flux density and of a
substantially zero remanent flux density, and of a permeability
much higher than 50, is coated over a substrate 1. The material of
this layer may be cobalt or an iron-cobalt alloy or, preferably,
pure iron which has a saturation flux density higher than that of
cobalt or of the iron-cobalt alloys. Iron can be evaporated at
temperatures compatible with these of the general process of
evaporation of the layers of the structure. The remanent induction
of iron is quite small and practically negligible with respect of
that of the "hard" material which will be later used in the
structure. The saturation flux density of evaporated iron
substantially equals 20,000 gauss whereas the corresponding
parametric value is about 18,000 for cobalt. The permeability of
iron, when evaporated in a thin layer or film at a substrate
temperature of about 200.degree. to 300.degree. C. with a thickness
of about twenty microns for instance, is from 100 to 300. The
saturation field of the layer, which can be considered as
corresponding to the anisotropy field of a uniaxial layer for the
purpose of the invention, may reach and even outpass 25 Oersteds
for identical geometrical dimensions.
Such a layer 2 is coated with a layer 3 the structure of which will
be hereinbelow defined. Over said layer 3 is coated a layer 4 of a
magnetic material having, with respect to the material of the layer
2, a lower saturation flux density, an appreciably higher
permeability and a value of anisotropy field appreciably lower than
the saturation field value of the layer 2. Illustratively, the
material of the layer 4 is an iron-nickel alloy having a saturation
field density of the order of 10,000 gauss, a permeability value
from 5000 to 1000 and an anisotropy field value of about 7
Oersteds, when evaporated to a substantially identical thickness as
the layer 2.
A flat coil winding 5 is formed over the above stack of layers
which, together, constitute one of the pole-pieces of the magnetic
circuit of the transducer. As presently well-known, such a flat
coil winding is made of a flat multi-turn helix of relatively
insulated conductors. The winding is applied by its front branch
over the stack of layers 2 to 4 and directly applies on the
substrate 1 by its lateral and rear branches of legs. Once formed,
it is completely coated with an insulating film 9, FIG. 4 except
its front face which is level to the airgap. In said front face at
least one insulated conductor of the winding is bare. The airgap
faces of the layers 2 to 4 and of the winding 5 are level with an
edge of the substrate 1. The length L3 of said edge equels the
length L1 of the layers 2 and 3 plus twice the width A of the
winding legs. The length L2 of the layer 4 is preferably made lower
than L1.
The thickness of the winding at its airgap face defines a
geometrical airgap for the transducer. The stack 2-3-4 constitutes
one of the pole-pieces of the magnetic circuit of the transducer
and the second pole-piece is formed over the winding and the stack
in symmetrical relation to the first, i.e., a layer 6 of same
material and geometry as the layer 4, a layer 7 of same structure
and geometry as the layer 3 and the layer 8 of same material and
geometry as layer 2. Illustratively though not imperatively, small
blocks such as shown at 11 in FIG. 4, may be formed in insulating
non-magnetic material of same thickness as the layer 6 on either
side of said layer over the front branch of the winding 5. The
composite layer 6-11 then provides a flat surface for deposition of
the layers 7 and 8 at this location of the structure. When such
blocks 11 are omitted, the layers 7 and 8 will reach the lateral
edges of the layer 6 up to the level of the top surface of the
winding airgap leg.
The structure of intervening layers 3 and 7 is such that they
create a magnetostatic decoupling between the layers 2 and 4,
respectively between the layers 6 and 8, so that the magnetizations
of the layers 4 and 6 cannot be disturbed by the magnetization of
the layers 2 and 8. Layers 2 and 8 are made of magnetically "hard"
material as apparent from the above whereas layers 4 and 6 are made
of magnetically "soft" material and, for an efficient operation of
the head comprised of said transducer structure, it is imperative
that the magnetizations of the soft layers cannot be influenced by
the magnetizations of the hard layers so that the soft layers may
preserve their easy magnetization axis parallel to the breadth of
the airgap.
The decoupling layers 3 and 7 may each consists of a nonmagnetic
dielectric material such for instance as Si0.sub.2 with a thickness
ensuring the required de-coupling of the above defined
magnztizations. As a modification, each of the said layers 3 and 7
may consists of a composite structure comprised of alternate thin
layers or films of soft and hard materials. The individual
thickness of such thin films is much lower than the thickness of
the layers between which they intervene, i.e., the layers 2 and 4
and the layers 6 and 8. In such a decoupling composite layer, the
thin films of magnetically hard material duly block the
magnetizations of the thin films of magnetically soft material but
the structure does not present any leakage magnetic field nor any
demagnetizing fields capable of influencing the layers between
which it is inserted, consequently ensuring the required decoupling
between said layers.
The second structure for the layer 3 is shown in FIG. 5 wherein the
thin layers 14, assumed of magnetically soft material, alternate
with the layers 15, assumed of magnetically hard material.
In FIG. 5 is further shown a modification of the structures of the
layers 2 and 4. Instead of forming such layers as "monolithic"
layers, layer 2 is made of a plurality of superposed relatively
insulated thin films 12 and layer 14 is similarly made of a
plurality of superposed relatively insulated thin films 13. The
material of the thin films 12 is a magnetically soft one. The
material of the thin films 13 is a magnetically hard one. The
relative insulation of the thin films is obtained by deposition of
very thin insulating films between the thin magnetic films. The
purpose of such an arrangement, which may, if desired, be provided
only for the magnetically soft material layers, is to enable an
optimalization of the dimensioning of the transducer, mainly of the
overall thickness of said transducer, as it eliminates the effect
of demagnetizing fields which, in "monolithic layers" will have
their paths imperatively closing through the hard material layers
in which they would sink through the air from the soft material
layers which generate such demagnetizing fields. Such demagnetizing
fields would create extraneous couplings of the magnetizations of
the soft and hard material layers, consequently enhancing the
possibilities of blocking the magnetization of the inner layers of
the pole-pieces unless exageration of the thickness of the
decoupling layers in said pole-pieces.
With a structure of transducer such as above desccibed and shown,
the layers 4 and 6 will have negligible action during a write-in
operation whereas the action of the layers 2 and 8 will be
efficient to define a width (e.sub.2, FIG. 4) of the magnetic
airgap. The recording fields will duly penetrate within the
recording magnetic layer moving along the direction of the arrow S
at close proximity of the airgap face of the transducer. On the
other hand, the action of the layers 2 and 8 will be nil during a
read-out operation from such a moving record and the layers 4 and 6
will define the width of the "read" airgap (e.sub. 1) which is
substantially equal to the width of the geometrical airgap e.
The lateral lengths of the soft and hard material layers have been
shown different as it is thought preferable to read on a reduced
length of the magnetic record with respect to the length over which
the record has been written. However, such a dimensioning is not
deemed imperative per se so that lengthes L2 and L1 may be made
equal if desired.
It may conclusively be stated that the magnetic transducer
structures according to the invention have their read and write
functions duly separated as the magnetically soft material layers
are relatively tightly coupled and do not have any substantial
leakage field therefrom and that, further, said soft material
layers are de-coupled from any magnetostatic damageable effect from
the hard material layers and are consequently protected against the
leakage fields from the said hard material layers.
* * * * *