Optical read-out magnetic head

An optical read-out magnetic head of a single pole type having a main pole, an auxiliary pole, and a writing coil. The main pole consists of a high permeability film and a magneto-optical film, the magneto-optical film has an easy magnetization axis parallel to or in the extension direction of that film surface high permeability film. Writing is carried out magnetically by employing the coil, and reproduction is effected optically by employing the magneto-optic film.

BACKGROUND OF THE INVENTION 
The present invention relates to a magnetic recording and reproducing head 
which can magnetically write and optically read out, and more particularly 
to a single pole magnetic head of write and read out composite type which 
is suitable to effect writing and reproducing by means of a single head. 
As recording/reproducing systems with high recording density, there are 
known a perpendicular magnetic recording and reproducing system and a 
magneto-optical writing and reproducing system. Further, there is also 
known a recording/reproducing system using a perpendicular magnetic head 
in recording and an optically read-out head utilizing magneto-optic effect 
in reproducing, with coupled use of the advantages of both systems. 
Heretofore, as a method for optically reproducing magnetized information 
from a recording medium by means of a magneto-optic effect (Faraday 
effect, Kerr effect and the like) by magnetically transferring it on a 
high permeability magnetic film perpendicularly disposed in close 
adjacency of a medium surface, there can be found a disclosure in the 
Japanese Patent Application Laid-Open, No. 1244/72 which is based upon 
U.S. Pat. No. 3,665,431. In case when such a device is used as a head for 
exclusive use in reproducing, a thin film material with large 
magneto-optical effect is sufficient to be used as a high permeability 
thin film, and can display a sufficient characteristic as a single layer. 
However, in order to write and reproduce at high speed in a magnetic disc 
apparatus, a magnetic tape device and the like, a structure should be 
devised which is capable to write and read out with the same head. In this 
respect, the above-mentioned example lacked the consideration on the 
function as a head for writing use. 
On the other hand, in a prior art optically reproducing type single pole 
magnetic head shown in FIG. 1, capable of writing and reproducing with the 
same head, a high permeability magnetic thin film 1 of the main pole was 
divided into two, and further there was arranged a second magnetic thin 
film 2, which had an easy magnetization axis in a direction perpendicular 
to the film surface and was closely adhered thereto, as described in the 
Japanese Patent Application Laid-Open, No. 169946/82. Thus, a polarized 
laser beam 9 was irradiated perpendicularly to this second thin magnetic 
film and the magnetized state of the main pole was discriminated by a the 
polar Kerr effect, the Faraday effect by perpendicularly incident optical 
beam, and the like. That is, the reproduction of high density recording 
was effected by converting the magnetization induced in the main pole from 
the magnetic medium into the difference of the strength of light. However, 
in this method, as shown in FIG. 1, since the second magnetic thin film 2 
is a perpendicular magnetizable film, almost all of the magnetic flux 4 in 
the magnetic circuit goes out from the magnetic circuit in the surface of 
the second magnetic thin film. Therefore, in such a construction, the 
magnetic circuit of the main pole becomes to have a large open end, and 
even when the magnetized state of the main pole is required to be reversed 
in dependence with a magnetic signal, it is necessary to expend extremely 
large energy. That is, it becomes difficult to let the magnetized state of 
the main magnetic pole faithfully follow the magnetic signal from the 
medium. As described above, in the above-described latter example, there 
lacked the consideration on the magnetic circuit construction for making 
an optical reproducing head with a high sensitivity. 
In FIG. 1, the symbol 3 designates the direction of magnetization, 5 the 
recording medium, 6 a substrate of the recording medium, 7 an auxillary 
magnetic pole and 8 a coil for writing. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a new type 
writing/reproducing composite type magnetic head which magnetically writes 
and optically reproduces by using the magneto-optical effect in a single 
pole type magnetic head, and more particularly to provide a 
writing/reproducing composite type magnetic head with a good signal versus 
noise ratio by forming a magnetic circuit construction wherein the 
magnetized induction is faithfully provoked for the magnetic signal from 
the medium in an optical read-out single pole magnetic head. 
In order to attain the above-described object, the optical read-out 
magnetic head of the present invention has such construction that in a 
single pole type magnetic head having a main pole, an auxiliary pole and a 
writing coil, the above-mentioned main pole has a first magnetic thin film 
having high permeability and high saturation magnetization and a second 
magnetic thin film having a large magneto-optic effect, such as the 
Faraday effect, the longitudinal Kerr effect and the like, and the 
above-mentioned second magnetic thin film is arranged to be capable of 
being magnetized by the leakage magnetic field from the recording medium, 
the said second magnetic thin film having an easy magnetization axis 
parallel to or in the film surface and the writing coil circumventing at 
least the first magnetic thin film of the main pole or the auxiliary pole. 
In the optical read-out magnetic head of the present invention, the writing 
for the recording medium is magnetically effected by means of said coil in 
the same manner as in the prior art perpendicular magnetic recording 
system, and the reading out of recorded signals from the recording medium 
is effected by the irradiation of the polarized laser beam on the surface 
of said second magnetic thin film and by measuring the change of polarized 
angle of the laser beam reflected therefrom to optically reproduce the 
recorded information. This optical reproducing method is fundamentally the 
same as the optical reproducing system using the magneto-optic effect in 
the prior art magneto-optical recording and reproducing system with the 
exception that the laser irradiated body is the second magnetic thin film 
mentioned above. 
As a recording medium for recording information by use of the magnetic head 
of the present invention, the prior art perpendicular magnetic recording 
medium may be used. 
For the above-described first magnetic thin film, a magnetic material 
having high permeability and high saturation magnetization, such as, for 
example, the known Fe-Ni alloy, Fe-N alloy, Co-Zr alloy or the like as in 
the main pole of a prior art perpendicular magnetic recording head may be 
used. In case when the crystallomagnetic anisotropy is present in the 
first magnetic thin film, it is desirable that the easy magnetization axis 
is present parallel to or in the film surface, but is not necessarily be 
limited to such a manner since the anisotropy is comparatively low in 
general. For said second magnetic thin film a magnetic material having 
large longitudinal Kerr effect and/or Faraday effect as well as an easy 
magnetization axis parallel to or in the film surface, such as, for 
example, magnetic garnet such as the known Y.sub.3 Fe.sub.5 O.sub.12 (a 
so-called YIG) and the like, a magnetic amorphous alloy consisting of a 
rare earth element and a transient metal element such as Gd-Co, or a 
magnetic amorphous alloy such as Fe-Co-B-P, Fe-B, Co-Zr or the like may be 
used. 
In order to arrange said second magnetic thin film to be capable of being 
magnetized by the leakage magnetic field from a recording medium, it is 
acceptable, for example, to magnetically couple the second magnetic thin 
film to said first magnetic thin film, or to arrange the second magnetic 
thin film at approximately right angles to and in close vicinity to the 
recording medium surface. In order to couple both members magnetically, it 
is recommended, for example, that the second magnetic thin film is 
laminated on the first magnetic film to form a main pole with a 
multi-layered structure, or that the first magnetic thin film is divided, 
with the divided first magnetic thin films being connected with the second 
magnetic thin film closely adhered thereto. 
Further, a reflection film may be provided in correspodence to needs to 
make the light path of the laser suitable. 
It is needless to say that a substrate for adhering the magnetic materials 
or the like thereon may be provided and a spacer formed of non-magnetic 
material may also be provided between layers of the multi-layered films.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
At first, in Examples 1-3, there are shown embodiments wherein the main 
pole of the single pole type magnetic head is formed in a multi-layered 
thin film structure. This multi-layered thin film structure consists of a 
first layer and a second layer. 
The first layer, that is, the first magnetic thin film is for exclusive use 
for writing, and is made of a magnetic thin film with high permeability 
and high saturation magnetization. The second layer, that is, the second 
magnetic thin film is for exclusive use for reproducing and is formed of a 
magnetic thin film having an easy magnetization axis parallel to or in the 
film surface and a magneto-optical high conversion efficiency and high 
permeability also. In case when required, in order to raise the writing 
efficiency of the first layer, a third film constituted of a non-magnetic 
material is provided between the first and second layers to disconnect the 
magnetic coupling between the first and second layers. 
EXAMPLE 1 
As shown in FIG. 2, in the single pole magnetic head of the present 
construction, the main pole has a double layer construction with a first 
layer 11 for writing exclusive use and a second layer 12 for reproducing 
exclusive use. The first layer is a ferromagnetic thin film made of a 
material with high permeability of 500-2000, and more preferably with a 
high saturation megnetization of 4.pi.Ms as (4.times.3.14.times.150) G 
such as the known FeNi, FeN or like. The second layer is made of a 
material having high magneto optical conversion efficiency of the Kerr 
effect and Faraday effect such as the known FeB, CoZr, GdCo, Y.sub.3 
Fe.sub.5 O.sub.12, etc., and preferably having a rotation angle of the 
polarization surface by the magneto-optical effect such as the Kerr 
rotation angle of 0.2.degree. or more. The auxiliary pole 16 consisting of 
a magnetic material such as Mn-Zn ferrite, Ni-Zn ferrite, Co-Zr alloy or 
the like is the one which returns the magnetic flux in the head to the 
side of the recording medium for closing the magnetic circuit. Further, at 
the lower side of the recording medium 14, there is disposed a planar 
magnetizable film 21 such as Permalloy on the like to let the magnetic 
pole be certainly closed. In FIG. 2, although the film 21 is disposed 
directly at the lower part of the medium, it may be provided in the lower 
part directly or indirectly. 
Also in FIG. 2, the arrow mark in the recording medium 14 designates the 
direction of magnetization, and the symbol 15 designates the substrate of 
the recording medium. Also, in the present embodiment, the auxiliary pole 
16 is provided on a non magnetic substrate such as, for example, glass, 
silicon or the like, and although there is provided with a spacer of a 
non-magnetic material such as, for example, SiO.sub.2 between part of the 
auxiliary pole 16 and the first layer 11 to form a stepped shape, either 
one of them is omitted in FIG. 2. Also, although a transparent cover layer 
consisting of a high molecular resin or the like is present on the second 
layer 12 and a reflecting film 19 is provided on the side surface thereof, 
these are also not shown in the figure. Also in FIGS. 3 and 4 the 
illustration of these eliminates are omitted. 
In the following, writing and reading out of information by the 
above-mentioned optically read-out magnetic head will be explained. 
At first, in writing, the main magnetic pole having film thickness of 0.1 
.mu.m and width of 3 .mu.m is excited with a coil 13 wound on the main 
pole such as, for example, for 8 turns. The saturation magnetization in 
the first layer is 4.times.3.14.times.250 G, and is larger than that of 
the second layer of 4.times.3.14.times.120 G, and by the strong magnetic 
flux mainly coming out of the forward end of the first layer, the 
perpendicular magnetic recording medium 14 such as CoCr, TbFe, CoO, etc. 
is magnetized to be written in with information. The reproduction is 
effected as described in the following. The leakage magnetic field from 
the magnetic domain written in the medium 14 magnetizes the forward end of 
the main pole. In this case, magnetization reverse is apt to occur in the 
second layer with a small saturation magnetization. A linearly polarized 
laser beam 17 (in this embodiment, a semiconductor laser of the wave 
length of 800 nm was used) is applied on the surface of the second layer 
as shown in the figure. 
The power of the laser beam was 0.1 to 5 mW at the film surface to be 
irradiated. 
In correspondence to the magnetized state of the second layer, Kerr 
rotation or Faraday rotation occurs and the change of magnetization can be 
converted into the change of the polarized angle. The reflected beam 18 
reaches the detector such as PIN diode or the like on the upper part of 
the head via the reflection film 19, lens optical system and the analyzer 
to carry out the reproduction of information as is well known. 
Next, the method for manufacturing the optically read-out magnetic head of 
the above described embodiment will be described. 
On a glass substrate with thickness of 1 mm, an auxiliary pole 16 made of 
MnZn ferrite 10 .mu.m thick was adhered by means of an ordinary organic 
adhesive or the like. Next, as a spacer, SiO.sub.2 of the thickness of 3 
.mu.m was laminated and adhered onto said ferrite by a sputtering method. 
In this case, approximately half of the ferrite surface was sputtered with 
SiO.sub.2 by being provided with an aluminium mask to let SiO.sub.2 not 
adhere on the ferrite at this part. Subsequently, said aluminium mask was 
dissolved by using nitric acid or the like to remove SiO.sub.2 on the 
aluminium mask to form a structure with a step formed with SiO.sub.2 on 
the surface of the ferrite. Then, a first layer 11 consisting of a known 
Fe-Ni alloy with high permeability was applied and laminated by the 
evaporation method or sputtering method to a thickness of 20-300 nm, or 
typically to a thickness of 100 nm. Further, a second layer 12 consisting 
of a known GdCo alloy with high magneto-optical conversion efficiency was 
applied and laminated to a thickness of 20-300 nm, or typically to a 
thickness of 100 nm. Subsequently, the multi-layered plate with five layer 
structure including the substrate and produced as shown above was cut by a 
cutting method such as an ion milling method to the width of 1 to 20 .mu.m 
or preferably to 1 to 3 .mu.m, and to a length of 10 to 300 .mu.m or 
typically to 100 .mu.m. Futher, a transparent cover layer of a polyimide 
resin or the like was provided on this multi-layered plate, and at the 
edge surface of the multi-layered plate, aluminium was evaporated to form 
a reflection film 19. The exciting coil 13 was formed by the known 
lithography method in the same manner as in the prior art thin film head 
or the like. 
EXAMPLE 2 
In the optically read-out magnetic head of this embodiment, as shown in 
FIG. 3, the second layer 102 for use in the optical read-out is formed 
only on the part to be irradiated by the beam, and the other parts are the 
same as in Example 1 of FIG. 2. In this case, the forward end of the main 
pole is formed only with the first layer 11, and the forward end film 
thickness can be reduced to 1 to 10 .mu.m, and typically to 3 .mu.m, so 
that high density writing and reproduction has become possible. In FIG. 3, 
the symbols indicating the parts other than the second layer 102 are the 
same as those in the case of FIG. 2. 
The optically read-out magnetic head of this embodiment can be produced by 
using a known thin film forming method such as the vacuum evaporation 
method or the sputtering method, and a known thin film patterning method 
by means of lithography, and the like as in the same manner as in Example 
1. 
EXAMPLE 3 
As shown in FIG. 4, a non-magnetic layer 100 of the thickness of 0.1 to 10 
.mu.m made of SiO.sub.2, AlN, or a resin was interposed between the first 
layer 11 and the second layer 202 to disconnect the magnetic coupling. 
Also, an auxiliary pole 206 was separated into two. The other parts are 
the same as in Example 1. In this case, the role participation of the 
writing film and the optically read-out film became more evident, and the 
formation of suitable thin film materials respectively became possible, 
while maintaining the function as a composite head. In FIG. 4, symbols 13, 
14, 15, 17, 18, 19 and 21 designate the same parts as in the case of FIG. 
2. 
The optically read-out magnetic head of this embodiment can also be 
produced by using a known thin film device production method as in the 
same manner as in Examples 1 and 2. 
The optically read-out magnetic head obtained in the above-described 
respective Examples, was improved in comparison with the prior art 
optically read-out magnetic head shown in FIG. 1, for approximately one 
order in the magneto-optical conversion efficiency and the reproducing 
efficiency. 
Next, in Examples 4 to 6, there are shown embodiments of the single pole 
type magnetic head having such structure that the main pole comprises the 
above-described first magnetic thin films divided into two and the 
above-described second magnetic thin film connecting said divided first 
magnetic thin films. That is, the main pole formed of the first high 
permeability thin film was divided into two, and in close adherence to 
these first thin films are arranged a second high permeability film having 
an easy magnetization axis in the direction parallel to the film surface 
while having a high longitudinal Kerr effect or Faraday effect. By means 
of such an arrangement, the magnetic circuits between the divided main 
magnetic poles are magnetically coupled to be closed by the second 
magnetic film and a faithful signal reproduction becomes possible to be 
carried out. 
EXAMPLE 4 
An shown in FIG. 5, the first magnetic thin film 31 consisting of a known 
high permeability film such as FeNi, CoZr, or the like with film thickness 
of 0.05 to 0.15 .mu.m and the width of 5 .mu.m is placed at right angles 
to and in close vicinity to a perpendicular magnetic recording medium 35 
such as CoCr, TbFe, CoO or the like. Also, the first magnetic thin film 31 
is divided into two as upper and lower parts. The permeability of the 
first magnetic film is preferably prepared to be 500 or more as in 
Examples 1 to 3. Further, a magnetic thin film for optical read-out, i.e. 
the second magnetic thin film 40 is arranged in close adherence to this 
first magnetic thin film. This thin film 40 has an easy magnetization axis 
in parallel to the direction in the film surface while it is a magnetic 
thin film with high magneto-optical conversion efficiency such as the 
longitudinal Kerr effect, Faraday effect and the like as in Examples 1 to 
3. For example, a magnetic garnet to begin with Y.sub.3 Fe.sub.5 O.sub.12 
(YIG), a rare earth metal-transition metal system amorphous alloy to begin 
with GdCo, an amorphous metal film such as FeCoBP and the like are used. 
Further, in opposite side to this main pole consisting of the first and 
second magnetic thin films, an auxiliary pole 37 consisting of a soft 
magnetic material such as Mn-Zn ferrite, Ni-Zn ferrite, Co-Zr alloy or the 
like and a writing coil (exciting coil) 38 are arranged in the reverse 
side of the medium. 
By the way, in FIG. 5, the symbol 33 denotes the direction of magnetization 
in the second magnetic thin film, the symbol 34 the magnetic flux, the 
sumbol 36 the substrate of the recording medium, and the arrow in the 
recording medium 35 the direction of magnetization in the medium. Further, 
although the first magnetic thin film 31 is provided on a non-magnetic 
substrate such as glass or the like, it is omitted in FIG. 5. 
Next, description will be given on the writing and reading of information 
by means of an optical read-out magnetic head of the present embodiment. 
At first, the writing is effected by exciting the auxiliary pole 37 by the 
coil 38 to magnetize the main pole 30, thereby to induce the magnetization 
of the perpendicular magnetic recording medium 35 directly disposed 
thereunder. The read out is carried out as follows: At first, the leakage 
magnetic field from the magnetic domain written in the medium 35 induces 
the magnetization of the first magnetic thin film 31 of the main pole 30 
to put it in order in one direction. Furthermore, this magnetization also 
causes the arrangement of the magnetization of the magneto-optical thin 
film i.e. the second magnetic thin film 40 closely adhered to the first 
magnetic thin film 31 into the same direction as that of the first 
magnetic thin film. When a linearly polarized laser beam 39 is made to be 
incident at an angle .theta. from the upper side obliquely, the beam 
reflects on the surface of the magneto-optic thin film (in the case of 
longitudinal Kerr effect) to become a reflected beam 41 and is passed 
through the lens optical system and a analyzer to be introduced into a 
photodetector such as a PIN diode or the like. At this instant, the 
polarized angle of the reflected beam rotates in proportion to 
Mscos.theta., when the magnetization of the opto-magnetic thin film is 
denoted as Ms. In dependence with the direction of the magnetization 
(upwards and downwards in the figure), this rotation angle changes the 
sign (anti-clockwise or clockwise rotation). Therefore, by detecting the 
sign of rotation angle, the direction of magnetization of the 
magneto-optic thin film, i.e. the second magnetic thin film 40, the 
direction of magnetization of the first magnetic thin film 31, and, 
further, the magnetization state of the medium 35 directly under the main 
pole can be reproduced according to the present embodiment. In the present 
Example, because the direction of magnetization of the magneto-optic thin 
film is made parallel to the film surface, the magnetic flux from the 
first magnetic thin film can be almost completely introduced into the 
magneto-optic thin film and the magnetic circuit in the beam irradiated 
part is closed to let the magneto-optic reproducing efficiency to be 
extremely high while enabling faithful reproduction for following the 
magnetization state of the medium. 
Next, explanation will be given on the method of manufacturing the 
optically read-out magnetic head of the present embodiment. 
An FeNi alloy thin film with the thickness of 50 to 1500 nm, or preferably 
100 nm, is formed on a flat substrate such as a glass or silicon plate 
with thickness of approximately 1 mm as the first magnetic film by means 
of the evaporation method or the sputtering method. Subsequently, the FeNi 
alloy thin film was divided and separated in the gap length of 100 to 1000 
nm by means of electron beam lithography method or photolithography method 
to provide a gap part. In this case, the length of the Fe-Ni alloy thin 
film at the side part of the magnetic recording medium was determined to 
be 10 to 50 .mu.m. In such a manner as to be able to connect the 
separately divided first magnetic thin films 31 on this gap, a thin film 
(the second magnetic thin film 40) of a material having an easy 
magnetization axis parallel to or in the film surface with a large 
magnetic Kerr effect such as a GdCo alloy was formed by the evaporation 
method or the sputtering method. As concerns the manufacturing method of 
the auxiliary pole 37 and the coil 38, they are quite the same as those in 
the prior art. 
EXAMPLE 5 
As shown in FIG. 6, a magneto-optic thin film having easy magnetization 
direction parallel to or in the plane of the film surface, i.e. the second 
magnetic thin film 310 was arranged in the intermediate position of the 
first magnetic film 31 divided into two, with the ends contacted thereto 
to form a main pole 30. In case where a transparent magnetic material such 
as Y.sub.3 Fe.sub.5 O.sub.12 is used, a reflecting film 42 of an aluminium 
thin film formed by the evaporation method is also provided. Moreover, a 
secondary reflection film 43 for directing the reflected beam 41 to the 
upper part of the disc of the recording medium is also arranged. In the 
case of the Example, the loss of the flux is small and the flux in the 
first magnetic thin film 31 is caused to be introduced into the 
magneto-optic thin film, i.e. the second magnetic thin film 310 ore 
efficiently than in the case of Example 4, and a preferable result can be 
obtained. 
Although not illustrated in FIG. 6, a transparent cover layer for 
supporting the secondary reflection film 43 is provided, and the secondary 
reflection film 43 is adhered to the side thereof. Further, symbols in 
FIG. 6 other than the above are the same as those in FIG. 5. 
The optical read-out magnetic head of this Example can be manufactured in 
the same manner as in Example 4 by using a thin film device manufacturing 
method utilizing the known thin film formation method such as the 
evaporation method or the sputtering method, and the known thin film 
patterning methods by means of lithography. 
EXAMPLE 6 
As shown in FIG. 7, an auxiliary pole 57 is provided on the same side as 
the main pole, and further, at the lower part of the perpendicular 
magnetic recording medium 55 is arranged a high permeability film 64 
(magnetization direction is in the suface). This planar magnetization film 
64 (Fe-Ni alloy called permalloy, or the like) functions when it is at the 
lower part of the medium, even if it is not provided in the direct low 
part of the medium. The structure in the circumference of the main pole is 
made as the same as in Example 5. In this case, the magnetic circuit 
becomes to be perfectly closed through the magneto-optic thin film, i.e. 
the second magnetic thin film 60 having the magnetization direction 
parallel to or in the surface, and the reproducing efficiency of the 
magnetic information from the medium can be made maximum. 
In FIG. 7, the symbol 51 denotes the first magnetic thin film, 56 the 
substrate of the magnetic recording medium, 58 a coil, 59 a linearly 
polarized lazer beam, 61 the reflected beam, 62 a reflection film, and 63 
a secondary reflection film. Further, the arrows in the recording medium 
indicates the direction of magnetization and the arrows in the other 
magnetic materials indicate magnetic flux. 
The optically read-out magnetic head of this Example can also be 
manufactured by using a known thin film device manufacturing method in the 
same manner as in Example 4 and 5. 
The optical read-out magnetic heads obtained by respective Examples in the 
above-described Examples 4 to 6 have been improved for about one order in 
the magneto-optic conversion efficiency and the reproduction efficiency in 
comparison to the prior art optical read-out magnetic head shown in FIG. 
1. 
As evident from the above-described Examples, according to the present 
invention, by making the magnetization direction of a thin film having the 
magneto-optic effect be parallel to the film surface, the flux from the 
high permeability film of the main pole has become induced to be 
approximately completely into the magneto-optic thin film, and the 
magneto-optic conversion efficiency and the reproduction efficiency have 
been improved for about one order in comparison wth the prior art ones 
shown in FIG. 1. Therefore, according to the present invention, the line 
direction period of a magnetic disc can be made so small as down to the 
order of the film thickness of 0.1 .mu.m of the main pole, and together 
with that, the track direction period can be made so small as to be equal 
to the laser beam diameter (1 to 5 .mu.m). As a result, the recording 
density could be improved to a large extent up to the region of 10 
bit/.mu.m.sup.2 which was impossible in the prior art.