In a magneto-optical disc apparatus using an initializing magnetic field generator, the magnetic field generator including a permanent magnet slides on or and floats above a surface of the magneto-optical disc for applying a magnetic field at a position on a track and precede to or follow a light beam spot irradiated by an optical head.

BACKGROUND OF THE INVENTION 
This invention relates to a magneto-optical disc apparatus for recording 
and reproducing data on a magneto-optical disc, and especially a 
magneto-optical disc having a magneto-optical recording medium with two or 
more different coercive force regions at room temperature. 
DESCRIPTION OF THE PRIOR ART 
A first art recognized technique includes a conventional magneto-optical 
disc apparatus using a magneto-optical disc satisfying the requirements of 
the ISO standard (hereinafter abbreviated as ISO magneto-optical disc), 
for recording a new data on a magneto-optical recording medium of the 
magneto-optical disc, in which old data previously recorded on tracks on 
the magneto-optical recording medium is erased. The new data is then 
recorded on the tracks. Thus, a predetermined inherent time is needed for 
recording data on the magneto-optical recording medium. 
In order to shorten the time for recording the data on the magneto-optical 
recording medium, a light intensity modulation overwriting technique is 
proposed. The light intensity modulation overwriting technique uses a 
magneto-optical recording medium having multi-layer configuration capable 
for directly overwriting the data on the recording medium. The recording 
medium includes a recording-reproducing layer having a first vertical 
magnetic anisotropy and a supplemental recording layer having a second 
vertical magnetic anisotropy which is different from the first vertical 
magnetic anisotropy of the recording-reproducing layer, (see: "Recording 
Power Characteristics of 130 mm Overwritable MO Disc by Laser Power 
Modulation Method" Japanese Journal of Applied Physics, Vol. 28 (1989) 
Supplement 28-3 pp. 367-370). 
The principle of the light intensity modulation overwriting technique is 
described with reference to FIG. 13. As can be seen from FIG. 13, a 
recording medium such as a magneto-optical disc 40 includes at least a 
referential layer 41 and a recording layer 42. The coercive force of the 
referential layer 41 is smaller than that of the recording layer 42 at the 
room temperature. The Curie temperature of the referential layer 41 is 
smaller than that of the recording layer 42 at the room temperature. The 
Curie temperature of the referential layer 41 is higher than that of the 
recording layer 42. In case of overwriting the data on the recording 
medium 40, an initializing magnetic field generator 43 is used for 
arranging the magnetization in each region of the referential layer 41 in 
the same direction. When the recording medium 40 moves or rotates in a 
direction shown by arrow 50 in the figure, the magnetization of the 
referential layer 41 is arranged in, for example, the downward direction 
by the magnetic field of the initializing magnetic field generator 43. 
However, the magnetization in each region of the recording layer 42 does 
not change, since the coercive force of the recording layer 42 is selected 
to be much higher than the intensity of the magnetic field due to the 
initializing magnetic field generator 43. 
A laser light beam 46 is focused on a surface of the recording medium 40 by 
an objective lens 45. The intensity of the laser light beam 46 can be 
provided at three levels, a lower powered level, a normal powered level 
and a higher powered level. When the data is overwritten on the recording 
medium 40, the laser light beams 46 is adjusted at the normal powered 
level and at the higher powered level. When the intensity of the laser 
light 46 is adjusted at the normal powered level, a temperature in a first 
portion 41a of the referential layer 41 and a temperature in a second 
portion 42a of the recording layer 42 respectively positioned below a 
region 49 is irradiated (hereinafter abbreviated as the laser irradiated 
region 49) respectively become higher than the Curie temperature of the 
recording layer 42, but lower than the Curie temperature of the 
referential layer 41. Accordingly, the magnetization in the second portion 
42a of the recording layer 42 positioned just below the laser irradiated 
region 49 will be erased. On the other hand, the magnetization in the 
first portion 41a of the referential layer 41 below the laser irradiated 
region 49 via the second portion 42a is not erased. At this time, a 
magnetic field due to a biasing magnetic field generator 44 exists in the 
first and second portions 41a and 42a positioned below the laser 
irradiated region 49. However, the intensity of the magnetic field due to 
the biasing magnetic field generator 44 is too weak to change the 
magnetization in the first portion 41a of the referential layer 41. When 
the second portion 42a of the recording layer 42 where the magnetization 
was erased has receded from the laser irradiated region 49, the 
temperature in the second portion 42a of the recording layer 42 becomes 
lower. Thus, the magnetization will appear in the second portion 42a of 
the recording layer 42 again. At this time, the magnetic exchange 
interacts between the referential layer 41 and the recording layer 42, so 
that the magnetization in the second portion 42a of the recording layer 42 
arranges in the same direction (downward in the figure) as the 
magnetization in the first portion 41a of the referential layer 41. 
When the intensity of the laser light 46 is adjusted at the higher powered 
level, the temperature in the first region 41a of the referential layer 41 
and the temperature in the second region 42a which are positioned below 
the laser irradiated region 49 respectively become higher than both the 
Curie temperature of the recording layer 42 and the Curie temperature of 
the referential layer 41. Accordingly, both the magnetization in the 
second portion 42a of the recording layer 42 and the magnetization in the 
first portion 41a of the referential layer 41 are erased. When the first 
portion 41a of the referential layer 41 and the second portion 42a of the 
recording layer 42 have receded from the laser irradiated region 49, the 
temperatures of the first and second portions 41a and 42a will decrease. 
The magnetization appears in the first portion 41a of the referential 
layer 41 faster than in the second portion 42a of the recording layer 42. 
At this time, the first portion 41a of the referential layer 41 is 
effected by the magnetic field due to the biasing magnetic field generator 
44, so that the magnetization in the first portion 41a turns reversely in 
upward direction in the figure. When the temperature of the first and 
second portions 41a and 42a further decrease, the magnetization in the 
second portion 42a of the recording layer 42 appears again. The 
magnetization in the second portion 42a of the recording layer 42 arranges 
in the same direction (upward direction in the figure) as the 
magnetization in the first portion 41a of the reference layer 41 due to 
the magnetic exchange interaction. 
By changing the intensity of the laser light beam 46 between the normal 
powered level and the higher powered level corresponding to digital 
information of "0" and "1" which are to be recorded, new data 48 can be 
directly overwritten on the recording medium 40 free from the old data 47. 
On the other hand, when the laser light beam is 46 is irradiated at the 
lower powered level for reproducing the data recorded on the recording 
medium 40, the temperature in the second portion 42a of the recording 
layer 42 positioned below the laser irradiated region 49 is lower than the 
Curie temperature of the recording layer 42, so that the magnetization in 
the second portion 42a of the recording layer 42 does not change. 
Accordingly, the data recorded on the recording layer 42 can be reproduced 
by detecting the direction of the magnetization in the second portion 42a 
of the recording layer 42 by using the lower powered level laser light 
beam 46. 
A second art recognized technique includes a multi-layer magneto-optical 
recording medium having two or more layers respectively having different 
coercive forces for increasing the recording density (more specifically, 
reproducing density). The data is read out from a region narrower than the 
diameter on the laser light spot. (see: NIKKEI ELECTRONICS, 1991.10.28 No. 
539, pp 223-233). This technique is called "Magnetically induced Super 
Resolution" (hereinafter abbreviated as MSR technique), since the super 
resolution effect can be obtain by utilizing the magnetic characteristics 
of magnetic layers different from each other due to the temperature. The 
MSR technique includes the Front Aperture Detection method (hereinafter 
abbreviated as FAD), the Rear Aperture Detection method (hereinafter 
abbreviated as D RAD). The FAD uses a recording medium having a recording 
layer, a insulating layer and a reproducing layer, and the data is read 
out from a lower temperature portion on the recording medium. The RAD uses 
a recording medium having a recording layer and a reproducing layer, and 
the data is read out from a higher temperature portion on the recording 
medium. The D-RAD uses a recording medium having a recording layer, a 
middle layer, a supplemental reproducing layer and a reproducing layer. 
The data is read out from a portion at a predetermined temperature on the 
recording medium. 
In the above-mentioned MSR techniques, the RAD and the D-RAD need a 
magnetic field generator for initializing the recording medium. In the 
RAD, the magnetic field generator is used for arranging the magnetization 
in the reproducing layer in the same direction. In the D-RAD, the magnetic 
field generator is used for arranging the magnetization of the 
supplemental reproducing layer and the reproducing layer in the same 
direction. Furthermore, both of the RAD and D-RAD need two magnetic field 
generators, and initializing magnetic field generator and a reproducing 
magnetic field generator. The initializing magnetic field generator 
generates a large intensity of the magnetic field for initializing the 
recording medium. The reproducing magnetic field generator generates a 
magnetic field in the opposite direction to and smaller than the magnetic 
field generated by the initializing magnetic field generator. The D-RAD is 
an improvement of the RAD, and is described with reference to FIGS. 14(a) 
and 14(b). FIG. 14(a) is a plan view showing a relation on a track or a 
recording medium seen from laser irradiation side. FIG. 14(b) is a 
cross-sectional side view of the recording medium. 
As can be seen from FIG. 14(b), the magneto-optical disc 60 includes a 
reproducing layer 63, a supplemental reproducing layer 64, a middle layer 
65, a recording layer 66, a substrate (not shown in the figure) and so on. 
Arrow 60 designates a moving direction along a track on the 
magneto-optical disc 60. Arrow 61 designates a direction of external 
magnet field applied for recording and reproducing the data. Arrow 62 
designates a magnetic field for initialing the magneto-optical disc 60. As 
shown in FIG. 14(a), when the data on the magneto-optical disc 60 is 
reproduced, a laser light spot 67 is focused along the track on the 
magneto-optical disc 60. 
When the laser light spot 67 is focused on the rotating magneto-optical 
disc 60, the temperature distribution of each magnetic layer, including 
the reproducing layer 63 and the supplemental reproducing layer 64, 
becomes rotationally asymmetric such as an oval shape as shown in FIG. 
14(a) in the rear side of the laser light spot 67. The temperature 
distribution can be considered to be divided into two regions of a high 
temperature region 69 and a middle temperature region 70. The high 
temperature region 68 is defined as a region where the temperature is 
higher than the Curie temperature Tc of the supplemental reproducing 
region 64. 
Signals (data) are assumed to be previously thermomagnetically recorded as 
recording magnetic domains 68 on the recording layer 66. The middle layer 
65 is provided for stabilizing the magnetic walls when the magnetization 
of the reproducing layer 68 coincides with that of the recording layer 66. 
The reproducing operation of the magneto-optical disc 60 is as follows. 
First, the magnetization in the reproducing layer 63 is arranged in the 
same direction (for example, downward in the figure) by an initializing 
magnetic field 62. When the laser light is irradiated on the 
magneto-optical disc 60 for reproducing the data, the temperature 
distribution such as the high temperature region 69 and the middle 
temperature region 70 occurs in each magnetic layer. In the reproducing 
layer 63, the coercive force is reduced due to the increase of the 
temperature, so that the magnetic exchange interaction between the 
reproducing layer 63 and the recording layer 66 governs in the middle 
temperature region 70. Thus, the magnetization in the reproducing layer 83 
is arranged in the same direction as the magnetization in the recording 
layer 66. On the other hand, the temperature in the high temperature 
region 69 in the supplemental reproducing layer 64 becomes higher than the 
Curie temperature of the supplemental reproducing layer 64, so that the 
magnetization in the supplemental reproducing layer 64 disappears. When 
the magnetization disappears, the magnetic exchange interaction between 
the reproducing layer 63 and the recording layer 66 corresponding to the 
high temperature region 69 will be intercepted. Thus, the magnetization in 
the reproducing layer 63 is governed by the reproducing magnetic field 61 
and the magnetization in the reproducing layer 63 is arranged in the same 
direction (for example, upward in the figure). 
With respect to the direction of the magnetization in the reproducing layer 
63 under the laser light spot 67, there are three regions. The 
magnetization in a first region is arranged in downward in the figure at 
all times by the effect of the initializing magnetic field. The 
magnetization in a second high temperature region is arranged in upward in 
the figure at all times by the biasing magnetic field. The magnetization 
in a third middle temperature region is arranged in the same direction as 
the magnetization in the recording magnetic domain 68. In the first and 
second regions, the magnetization is arranged in the constant direction at 
all times, so that data or information cannot be obtained from the first 
and second regions. The data or information in the recording layer 66 can 
be obtained only from a region where the laser light spot 67 and the 
middle temperature region 70 are overlapped. The other region where the 
laser light spot 67 is irradiated can be regarded as substantially masked. 
In other word, even when the recording magnetic domain 68 is much smaller 
than the laser light spot 67, the data recorded in the recording magnetic 
domain 68 can be reproduced. Thus, a high density reproducing can be 
achieved. 
The above-mentioned techniques relate to the recording and reproducing 
media. On the other hand, with respect to the single use of reproducing 
media, a method for increasing the recording density by using a super 
resolution method is discussed in, for example, Publication Gazette of 
Unexamined Japanese Patent Application Hei 5-266523. The third art 
recognized technique includes a first dielectric layer, a recording layer 
made of magnetic material, a second dielectric layer and a reflection 
layer serially laminated on a transparent substrate. Marks which are 
gathering of minute convex and concave are formed on the surface of the 
transparent substrate. Data or information is defined by the marks, and 
the marks are transferred to a surface shape of the first dielectric 
layer. Furthermore, the surface shape of the first dielectric layer is 
reflected to the change of coercive force of the recording layer which is 
disposed above the first dielectric layer. More specifically, the coercive 
force Hm in marked portions in the recording layer disposed above the 
marks is selected to be relatively larger, and the coercive force Hn in 
the other non-marked portions are selected to be relatively smaller. In 
other word, the third technique relates to the super resolution 
reproducing method using the recording media in which the coercive force 
in marked portions is different from the other portions. 
In a first reproducing method, an initializing magnetic field H1 which is 
larger than the coercive force Hm in the marked portions and the coercive 
force Hn in the non-marked portions and has a predetermined constant 
direction is applied to the recording medium. Thus, the marked portions 
and the non-marked portions are magnetized in the same direction. After 
applying the initializing magnetic field H1, a reversing magnetic field 
H2, which has an intensity between Hm and Hn and has a direction opposite 
to the initializing magnetic field H1, is applied for reversing the 
magnetization direction in the non-marked portions. Thus, the 
magnetization in the marked portions is reversed to that in the non-marked 
portions. Under this condition, when a light beam, which is relatively 
intensive so as to erase the magnetization in the marked portions and the 
non-marked portions in the rear of the light beam spot, is irradiated on 
the recording medium, a signal can be detected from the portion in ahead 
of the light beam spot. Thus, a signal from the marked portion which is 
narrower than the light beam spot can be obtained. In this method, an 
initializing magnetic field generator and the reversing magnetic field 
generator are necessarily disposed in ahead of the light beam spot. 
In a second reproducing method, the initializing magnetic field generator 
(intensity of output magnetic field H1) is disposed in ahead of the light 
beam spot, and both of the marked portions are magnetized in a 
predetermined direction. After that, a relatively weak biasing magnetic 
field H3 is applied while the reproducing light beam is of the magnetic 
field H3) is provided in the vicinity of the region where the reproducing 
light beam is irradiated. At this time, power of laser light beam is 
controlled to heat the recording layer at a temperature lower than the 
Curie temperature of the recording layer in a manner so that only the 
magnetization in the non-marked portions in which the coercive force is 
relatively small turns reversely by the biasing magnetic field H3, but the 
magnetization in the marked portions in which the coercive force is 
relatively large is not turned. By such operations, the magnetization in 
the non-marked portions where the temperature reaches a predetermined 
value turns in a region where the reproducing laser light beam is 
irradiated, and the change of the magnetization can be detected as a 
signal. As a result, high density reproduction can be achieved. 
The above-mentioned first technique needs an initializing magnetic field 
generator for generating an intense magnetic field of such as 2-5 
kilooersted on the recording medium and a recording magnetic field 
generator for generating the magnetic field of several hundreds oersted. 
The above-mentioned second technique needs an initializing magnetic field 
generator for an intense magnetic field of such as 2-5 kilooersted on the 
recording medium and a reproducing magnetic field generator for generating 
the magnetic field of several hundreds oersted. 
The first reproducing method in the third technique needs an initializing 
magnetic field generator for generating an intense magnetic field of such 
as 2-5 kilooersted on the recording medium and a reversing magnetic field 
generator for generating the magnetic field generator for generating the 
magnetic field H2 of several hundreds oersted, which has an intensity 
between Hm and Hn and has a direction opposite to the initializing 
magnetic field H1, is applied for reversing the magnetization direction in 
the non-marked portions. The second reproducing method in the third 
technique needs an initializing magnetic field generator for generating an 
intense magnetic field of such as 2-5 kilooersted on the recording medium 
and a biasing magnetic field generator for generating the biasing magnetic 
field of several hundreds oersted for reversing the magnetization in the 
non-marked region. 
Namely, each of the above-mentioned techniques involves a first 
(initializing) magnetic field generator for generating 2-5 kilooersted and 
a second magnetic generator for generating the magnetic field of several 
hundreds oersted. It, however, is very difficult to dispose a second 
magnetic field generator under the condition that a magnetic field having 
an intensity sufficient to prevent the contact of the initializing 
magnetic field generator and the recording medium is applied to the 
recording medium. Actually, in a conventional apparatus using the ISO 3.5 
inch type cartridge of the disc, the opening of the cartridge is too 
narrow to provide two magnetic field generators. If a magnetic field 
generators are forcibly provided in the opening, the intensity of the 
magnetic field generated by the initializing magnetic field generator is 
larger, so that the magnetic field leaks into an objective lens actuator, 
and the objective lens moves abnormally. Furthermore, the magnetic field 
generated by the second magnetic field generator is affected by the 
magnetic field generated by the initializing magnetic field generator, so 
that the intensity of the magnetic field generated by the second magnetic 
field generator cannot be controlled to the desired value. 
SUMMARY OF THE INVENTION 
An objective of this invention is to provide an improved magneto-optical 
disc apparatus in which the initializing magnetic field generator and the 
biasing magnetic field generator, if necessary, can be disposed in a 
narrow space without affecting the objective lens actuator. 
A first magneto-optical disc apparatus according to this invention uses a 
magneto-optical disc including a magneto-optical recording medium having 
at least two kinds of coercive forces at room temperature. A second 
magneto-optical disc apparatus uses a magneto-optical disc including a 
magneto-optical recording medium configured by at least two magnetic 
layers respectively having magnetic exchange interaction. 
In both of the first and second magneto-optical apparatus of this 
invention, an optical head is moved in the radial direction of the 
magneto-optical disc and irradiates a light beam spot on a track on the 
magneto-optical disc. A magnetic field generator includes at least a 
permanent magnet and slides on or floats above a surface of the 
magneto-optical disc for applying a magnetic field at a position on the 
track which is in ahead of or behind the light beam spot. 
The magnetic field generator slides on or floats above the surface of 
magneto-optical disc, so that the distance between the magnetic field 
generator and the surface of the magneto-optical disc can be made very 
short. Thus, when a compact permanent magnet is used as the magnetic field 
generator, the magnetic field having a sufficient intensity can be 
obtained. Furthermore, an area of the permanent magnet facing the surface 
of the magneto-optical disc can be made a square of about two or less 
millimeters. Therefore, the initializing magnetic field generator can be 
provided in a compact magneto-optical disc apparatus using the ISO 3.5 
inch type magneto-optical. 
Furthermore, the magnetic field generator moves in ahead of or behind the 
light beam spot on the track of the magneto-optical disc, so that the 
diameter of the magnetic flux for initializing the disc can be made very 
small. Thus, the initializing magnetic field generator of this invention 
can readily be designed rather than the conventional initializing magnetic 
field generator. As a result, the magneto-optical disc apparatus of this 
invention can be downsized. Furthermore, size of the magnetic field 
generator of this invention can be made smaller, so that the area where 
the magnetic field leaks can be much smaller than that of conventional 
apparatuses. As a result, any affect on the objective lens actuator of the 
optical head due to the leakage of the magnetic field can be reduced. 
In the above-mentioned first magneto-optical disc apparatus, it is 
preferable that the intensity of the magnetic field generated by the 
magnetic field generator is larger than at least one coercive force (for 
example, Hc1) of the magneto-optical recording medium and smaller than at 
least one of the remained coercive forces (for example, Hc2) of the 
magneto-optical recording medium. Alternatively, it is preferable that the 
magnetic field generator has a plurality of magnetic field generating 
portions on a surface facing the magneto-optical disc, an intensity of a 
magnetic field generated by one of the magnetic field generating portion 
is larger than at least one coercive force (for example, Hc1) of the 
magneto-optical recording medium, and an intensity of a magnetic field 
generated by one of other magnetic field generating portions is smaller 
than at least one of remained coercive forces (for example, Hc2) of the 
magneto-optical recording medium. By such configurations, portions of the 
magneto-optical recording medium having the coercive force of Hc1 can be 
initialized to arrange the magnetization in the same direction without 
changing the magnetization in portions having the coercive force of Hc2. 
In the above-mentioned second magneto-optical disc apparatus, it is 
preferable that the magnetic field generator has a plurality of magnetic 
field generating portions on a surface facing the magneto-optical disc 
with at least one of the magnetic field generating portions being disposed 
so as to apply a magnetic field to a position in ahead of or behind the 
light beam spot on the magneto-optical disc. By such a configuration, the 
initialization of the magneto-optical recording medium, recording and 
reproducing of the data on the recording medium can be operated by one 
magnetic field generator. 
Furthermore, in the above-mentioned second magneto-optical disc apparatus, 
it is preferable that the magnetic field generator comprises a first 
magnetic field generating portion including a permanent magnet and a 
second magnetic field generating portion including a coiled electromagnet, 
the first magnetic field generating portion is disposed in a manner so as 
to apply a magnetic field at a position precede to or follow to the light 
beam spot on the magneto-optical disc, and the second magnetic field 
generating portion is disposed at a position in a manner so as to apply a 
magnetic field at the position of the light beam spot. By such a 
configuration, when the polarity of the magnetic field generated by the 
electromagnet is changed alternatively, the electromagnet can be used not 
only for recording the data on the magneto-optical recording medium but 
also for reproducing the data recorded on the magneto-optical recording 
medium. Furthermore, the electromagnet is provided on the sliding or 
floating magnetic field generator which slides on or floats above the 
magneto-optical disc, so that the apparatus of this invention can be 
downsized and electric power consumption can be reduced in comparison with 
the conventional apparatus using a fixed electromagnet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
A first embodiment of a megneto-optical disc apparatus of this invention is 
described with reference to FIG. 1(a) (plan view) and FIG. 1(b) (side 
view). As can be seen from FIGS. 1(a) and 1(b), the magneto-optical disc 
apparatus comprises a magneto-optical disc 1, a spindle motor 2 for 
rotating the magneto-optical disc 1, an optical head 3, a first magnetic 
field generator 4, a link arm 5, a suspension 6, and a second magnetic 
field generator 8. Numeral 7 designates a light beam emitted from the 
optical head 3 in FIG. 1(b). The magneto-optical disc 1 rotates in 
counterclockwise direction as shown by arrow 9 in FIG. 1(a). Numeral 10 
designates a track on the magneto-optical disc 1 in FIG. 1(a). The 
magneto-optical disc 10 includes a magneto-optical recording medium having 
at least two layers respectively having different coercive forces, for 
example Hcl and Hc2 at room temperature. 
There are three types of the magneto-optical disc 1 which can be used in 
the magneto-optical disc apparatus of this invention. A first 
magneto-optical disc 1 (hereinafter abbreviated as A-type disc) relates to 
a direct overwriting system similar to the magneto-optical disc used in 
the first prior art technique. The A-type disc comprises a magneto-optical 
recording medium formed on a substrate made of resin such as a 
polycarbonate. The magneto-optical recording medium has a multi layer 
structure including a recording and reproducing layer having vertical 
magnetic anisotropy, and a supplemental recording layer having a different 
coercive force from that of the recording and reproducing layer. 
A second magneto-optical disc 1 (hereinafter abbreviated as B-type disc) 
corresponds to the magnetically induced super resolution (MSR) method 
similar to the magneto-optical disc used in the second prior art 
technique. In particular, the B-type disc relates to the RAD or D-RAD 
method which requires an initializing magnetic field. In the MSR method, 
data can be read out from a region narrower than the area of the light 
beam spot, so that the recording density (specifically, reproducing 
density) can be increased. 
A third magneto-optical disc 1 (hereinafter abbreviated as C-type disc) has 
a single use for reproduction similar to the magneto-optical disc used in 
the third prior art technique. The C-type disc can have a high reproducing 
density using the MSR method. 
In the A-type disc and the B-type disc, the magneto-optical recording 
medium is formed by a plurality of magnetic layers respectively having 
different coercive forces. In the C-type disc, however, the coercive force 
in a magnetic layer positioned above the marked portions is different from 
that in the same magnetic layer positioned above the non-marked portions. 
In this invention, these three types of the magneto-optical disc can be 
used, and the initializing magnetic field is necessary in each case. 
The spindle motor 2 rotates the magneto-optical disc 1 in counterclockwise 
direction sown by arrow 9. The optical head 3 is moved by an driving 
mechanism (not shown in the figure) for accessing a desired position on 
the magneto-optical disc 1. When the magneto-optical disc 1 is a A-type or 
B-type, the optical head 3 records and reproduces the data about the 
magneto-optical disc 1. On the other hand, when the magneto-optical disc 1 
is a C-type, the optical head 3 only reproduces the data from the 
magneto-optical disc 1. The light beam 7 is irradiated on a surface of a 
magneto-optical recording medium of the magneto-optical disc 1 for 
recording and reproducing the data. With respect to the magneto-optical 
disc 1 is C-type of single use for reproduction, the light beam 7 is 
correctly irradiated on the reproducing medium. However, the data is 
previously recorded on the reproducing medium. Thus, the term "recording 
medium" used in this disclosure includes not only "recording" but also 
"reproducing". 
The optical head 3 is connected to the link arm 5. The first magnetic field 
generator 4 is connected to the link arm 5 via suspension 6 having 
elasticity. The suspension 6 and the link arm 5 are connected by a hinge 
(not shown in the figure) by which the first magnetic field generator 4 is 
raised when the magneto-optical disc 1 is interchanged. Thus, the first 
magnetic field generator 4 moves corresponding to the access movement of 
the optical head 3. A permanent magnet is mounted on the first magnetic 
field generator 4. The first magnetic field generator 4 slides on or 
floats above the surface of the magneto-optical disc 1. 
The first magnetic field generator 4 and the optical head 3 are 
respectively positioned above and below the magneto-optical disc 1 and 
facing to each other via the magneto-optical disc 1. Furthermore, the 
first magnetic field generator 4 and the optical head 3 are positioned in 
ahead of or behind the light beam spot due to the light beam 7. In the 
first embodiment, the first magnetic field generator 4 is positioned in 
ahead of the light beam spot. 
The light beam 7 is focused on the track 10 on the magneto-optical disc 1, 
so that the first magnetic field generator 4 should be positioned in a 
manner so as to apply the magnetic field on the track 10. As can be seen 
from FIGS. 1(a) and 1(b), the optical head 3 moves along a line crossing 
the rotation axis of the magneto-optical disc 1, that is the radial 
direction of the magneto-optical disc 1. On the other hand, the first 
magnetic field generator 4 moves in parallel with the movement of the 
optical head 3. Accordingly, with respect to the access point on the 
magneto-optical disc 1 by the first magnetic field generator 4 or the 
radius of the track 10, a minute discrepancy occurs between the position 
of the light beam 7 by the optical head 3 and the position of the first 
magnetic field generator 4. Thus, the area of a magnetic field generated 
by the first magnetic field generator 4 should cover a predetermined 
scope. 
The second magnetic field generator 8 is disposed so as to cover all the 
tracks on the magneto-optical disc 1. When the magneto-optical disc 1 is a 
A-type, the second magnetic field generator 8 serves as a biasing magnetic 
field generator, and capable of generating the direct magnetic field 
having the intensity of about 300 oersted. Accordingly, a bar shaped 
permanent magnet can preferably be used for the second magnetic field 
generator 8. Furthermore, since the demanded intensity of the magnetic 
field is small, an electromagnet can be used for the second magnetic field 
generator 8. The distance between the second magnetic field generator 8 
and the magneto-optical disc 1 is preferably about 1 mm. 
When the magneto-optical disc 1 is the B-type, the second magnetic field 
generator 8 serves as a biasing magnetic field generator for generating 
the biasing magnetic field in the erasing and recording operation of the 
data, and a reproducing magnetic field generator for generating a 
necessary reproducing magnetic field in the reproducing operation of the 
data. Since the polarity of the magnetic field must be changed 
corresponding to the recording and the erasing operation of the data, a 
rotatable bar shaped permanent magnet or an electromagnet is preferably 
used as the second magnetic field generator 8. 
When the magneto-optical disc 1 is the C-type, the second magnetic field 
generator 8 is used for reversing the magnetization in the non-marked 
portions on the magneto-optical disc where the coercive force is small. 
Thus, a bar shaped permanent magnet or an electromagnet can preferably be 
used as the second magnetic field generator 8. 
Detailed configuration of the first magnetic field generator 4 will be 
described referring to FIGS. 2(a) to 5(b). FIG. 2(a) is the side view of 
the sliding type first magnetic field generator 4, and FIG. 2(b) is the 
plan view thereof FIG. 3(a) is the side view of the sliding type first 
magnetic field generator 4, and FIG. 3(b) is the plan view thereof The 
configuration on a magnet 22 disposed inside the first magnetic field 
generator 4 shown in FIGS. 2(a) and 2(b) is different from that shown in 
FIGS. 3(a) and 3(b). 
As can be seen from the figures, in the first magnetic field generator 4, 
chamber is provided on the molded block 20 for forming a sliding face 21, 
and a permanent magnet 22 is provided inside the molded block 20. The 
sliding direction of the first magnetic field generator 4 is designated by 
reference numeral 23. When the intensity of the magnetic field needs more 
than 2 kilooersted, a permanent magnet made of a rare earth material is 
preferably used as the magnet 22. The permanent magnet 22 is mounted on 
the molded block 20 in a manner so that a surface of the magnet 22 is a 
little hollowed in order not to protrude from the sliding surface 21. In 
the figures, the suspension 6 is omitted. However, the conventional 
suspension used in the widely used floppy disc drive can be used as the 
suspension 6. In the embodiment shown in FIGS. 2(a) and 2(b), a bar shaped 
permanent magnet is preferably used as the magnet 22. In another 
embodiment shown in FIGS. 3(a) and 3(b), a U-shaped permanent magnet is 
used as the magnet 22. In case of using the U-shaped permanent magnet, the 
intensity of the magnetic field can be made larger than where a bar shaped 
magnet is used. The shapes of the permanent magnet 22 are not restricted 
by these embodiments, and other shapes can be designed corresponding to 
the objective of the magneto-optical disc apparatus. 
FIG. 4(a) is the side view of the floating type first magnetic field 
generator 4, and FIG. 4(b) is the plan view thereof FIG. 5(a) is the side 
view of the floating type first magnetic field generator 4, and FIG. 5(b) 
is the plan view thereof The configuration on a magnet 22 disposed inside 
the first magnetic field generator 4 shown in FIGS. 4(a) and 4(b) is 
different from that shown in FIGS. 5(a) and 5(b). 
As can be seen from the figures, the floating type first magnetic field 
generator 4 has characteristics on the sliding surface 21. An air intake 
24 is formed at the front end of the sliding surface 21 for taking the air 
for floating the first magnetic field generator 4. Furthermore, in order 
to stabilize the floating of the first magnetic field generator 4, grooves 
25 are formed on the sliding surface 21. The other configurations are 
substantially the same as the above-mentioned sliding types. The floating 
type first magnetic field generator 4 is suitable to the magneto-optical 
disc apparatus in which the magneto-optical disc 1 rotates in a high 
speed, since the floating first magnetic field generator does not 
significantly damage the surface of the magneto-optical disc 1. 
Since the first magnetic field generator 1 in the magneto-optical disc 
apparatus according to the first embodiment is the sliding type or the 
floating type, the distance between the sliding surface 21 of the first 
magnetic field generator 4 and the surface of the magneto-optical disc 1 
is very short. Thus, the permanent magnet or the electromagnet can be made 
smaller for generating the necessary intensity of the magnetic field in 
the magneto-optical recording medium of the magneto-optical disc 1. 
Furthermore, since the size of the permanent magnet or the electromagnet 
can be decreased, they can readily be mounted inside the first magnetic 
field generator 4. An area for facing the magneto-optical disc 1 can be 
made a square of about two or less millimeters, so that the initializing 
magnetic field generator has sufficient room to be disposed in the 
conventional ISO 3.5 inch type magneto-optical disc apparatus. As a 
result, the magnetic field generator of this invention has a number of 
degrees of freedom of design in comparison with the conventional magnetic 
field generator, and the downsizing of the magneto-optical disc apparatus 
can be achieved. 
Second Embodiment 
A second embodiment of a magneto-optical disc apparatus of this invention 
is illustrated by way of FIG. 8(a) (plan view) and FIG. 6(b) (side view). 
As can be seen from FIGS. 6(a) and 6(b), the magneto-optical disc 
apparatus comprises a magneto-optical disc 1, a spindle motor 2 for 
rotating the magneto-optical disc 1, an optical head 3, a magnetic field 
generator 11, a link arm 5, and a suspension 6. Numeral 7 designates a 
light beam emitted from the optical head 3 in FIG. 6(b). The 
magneto-optical disc 1 rotates in counterclockwise direction as shown by 
arrow 9 in FIG. 6(a). Numeral 10 designates a track on the magneto-optical 
disc 1 in FIG. 6(a). 
The above-mentioned magneto-optical disc apparatus according to the first 
embodiment requires a first magnetic field generator 4 for generation an 
intense magnetic field and a second magnetic field generator 8 for 
generating a weak magnetic field. On the other hand, in the 
magneto-optical disc apparatus according to the second embodiment, the 
magnetic field generators for the intense magnetic field and for the weak 
magnetic field are commonly integrated in the same magnetic field 
generator 11. Thus, the mechanical movement of the magnetic field 
generator 11 in the second embodiment in the interchanging of the 
magneto-optical disc 1 is substantially the same as the movement of the 
first magnetic field generator 4 in the first embodiment. Furthermore, the 
other configurations of the magneto-optical disc apparatus according to 
the second embodiment are substantially the same as those of the above 
mentioned magneto-optical disc apparatus according to the first 
embodiment, so that the explanation of them are omitted. The kinds of the 
magneto-optical disc 1 used in the second embodiment correspond to the 
A-type, B-type and C-type discs described with respect to the first 
embodiment. 
Detailed configuration of the magnetic field generator 11 in the 
magneto-optical disc apparatus according to the second embodiment is 
described referring to the FIG. 7(a) to FIG. 12(b). FIG. 7(a) is the side 
view of the sliding type magnetic field generator 11 in which only a 
permanent magnet is mounted, and FIG. 7(b) is the plan view thereof FIG. 
8(a) is the side view of the sliding type magnetic field generator 11 in 
which only a permanent magnet is mounted, and FIG. 8(b) is the plan view 
thereof. Both embodiments of the magnetic field generator 11 are used for 
the A-type and C-type magneto-optical disc, since the fixed magnetic field 
is used for reproducing the magneto-optical disc of A-type and C-type, and 
the source for generating the magnetic field mounted in the magnetic field 
generator 11 is the permanent magnet which can not be changed the 
direction of the magnetic field. The configuration of the permanent 
magnets 22 disposed inside the magnetic field generator 11 shown in FIGS. 
7(a) and 7(b) is different from those shown in FIGS. 8(a) and 8(b). 
In both embodiments, a plurality of magnetic poles 22a, 22b appears on the 
sliding surface 21. In the embodiment shown in FIGS. 7(a) and 7(b), a 
plurality of, for example, two bar shaped permanent magnets 22 are mounted 
inside the molded block 20 of the magnetic field generator 11. In the 
embodiment shown in FIGS. 8(a) and 8(b), a permanent magnet 22 having a 
channel shaped cross-section is mounted inside the molded block 20 of the 
magnetic field generator 11. One magnetic pole, for example, 22a is 
disposed in a manner so as to apply a magnetic field on a position of 
light beam irradiation on the magneto-optical disc 1. When the intensity 
of the magnetic field due to the magnetic pole 22a is Hb and the intensity 
of the initializing magnetic field due to the magnetic pole 22b is Hi, the 
intensity Hb and Hi are set to be Hb&lt;Hi. In the embodiment shown in FIGS. 
7(a) and 7(b), two permanent magnets 22 respectively having different 
magnetization are prepared with the one having the weaker magnetization 
being disposed at the position of the magnetic pole 22a. In the embodiment 
shown in FIGS. 8(a) and 8(b), for reducing the intensity of the magnetic 
field Hb by the magnetic pole 22a, a leg 221 of the permanent magnet 22 
disposed on the side of the magnetic pole 22a is largely hollowed from the 
sliding surface 21 than a leg 222 disposed on the side of the other 
magnetic pole 22b. 
FIG. 9(a) is the side view of the sliding type magnetic field generator 11 
in which a permanent magnet 22 and an electromagnet 26 are mounted, and 
FIG. 9(b) is the plan view thereof The magnetic field generator 11 shown 
in FIGS. 9(a) and 9(b) is used for the magneto-optical disc of B-type. By 
changing the polarity of the electromagnet 26, the biasing magnetic fields 
for recording and erasing operation of the data can be generated. The 
reproducing magnetic field is also generated by the electromagnet 26 in 
reproducing operation of the data. The electromagnet 26 is disposed so as 
to apply the biasing magnetic field in erasing the data and the 
reproducing magnetic field in reproducing the data at a position of the 
light beam irradiation on the magneto-optical disc 1. 
FIG. 10(a) is the side view of the floating type magnetic field generator 
11 in which only two permanent magnets 22 are mounted, and FIG. 10(b) is 
the plan view thereof FIG. 11(a) is the side view of the floating type 
magnetic field generator 11 in which only a permanent magnet 22 is 
mounted, and FIG. 11(b) is the plan view thereof Both embodiments of the 
magnetic field generator 11 are used for the A-type and C-type 
magneto-optical disc similar to the above-mentioned embodiments shown in 
FIGS. 7(a), 7(b), 8(a) and 8(b), since the fixed magnetic field is used 
for reproducing the magneto-optical disc of A-type and C-type, and the 
source for generating the magnetic field mounted in the magnetic field 
generator 11 is the permanent magnet which can not be changed the 
direction of the magnetic field. The configuration of the permanent 
magnets 22 disposed inside the magnetic field generator 11 shown in FIGS. 
10(a) and 10(b) is different from those shown in FIGS. 11(a) and 11(b). 
FIG. 12(a) is the side view of the floating type magnetic field generator 
11 in which a permanent magnet 22 and an electromagnet 26 are mounted, and 
FIG. 12(b) is the plan view thereof. As can be seen from the figures, the 
floating type magnetic field generator 11has characteristics on the 
sliding surface 21. An air intake 24 is formed at the front end of the 
sliding surface 21 for taking the air for floating the magnetic field 
generator 11. Furthermore, in order to stabilize the floating of the 
magnetic field generator 11, grooves 25 are formed on the sliding surface 
21. The other configurations are substantially the same as the 
above-mentioned sliding types shown in FIGS. 7(a) to 9(b). The floating 
type magnetic field generator 11 is suitable to the magneto-optical disc 
apparatus in which the magneto-optical disc 1 rotates in a high speed, 
since the floating first magnetic field generator does not damage the 
surface of the magneto-optical disc 1 so much. 
As mentioned above, the magneto-optical disc apparatus according to the 
second embodiment can generate a plurality of magnetic fields about 
respective A-type, B-type and C-type of magneto-optical discs with only 
one magnetic field generator 11. Thus, more compact magneto-optical disc 
apparatus can be provided. Especially, the electromagnet 26 mounted inside 
the magnetic field generator 11 as shown in FIGS. 9(a), 9(b), 12(a) and 
12(b) is very compact, so that the consuming of the electric power becomes 
very smaller than that of the conventional apparatus using a large fixed 
electromagnet. 
Furthermore, in the above-mentioned first and second configurations, the 
configurations or shapes of the permanent magnet 22 and/or the 
electromagnet 26 are not restricted in the embodiment shown in the 
figures. The polarity of the magnets shown by symbols of "S" and "N" in 
the figures are conveniently used, and the polarity of the magnet can be 
changeable responding to the configuration or kinds of the magnetic layer 
of the magneto-optical discs 1 which is used in the magneto-optical disc 
apparatus of this invention. 
The invention may be embodied in other specific forms without departing 
from the spirit and scope thereof The embodiments are to be considered in 
all respects as illustrative and not restrictive. The scope of the 
invention is indicated by the appended claims rather than by the foregoing 
description, and all changes which come within the meaning and range of 
equivalency of the claims are intended to be embraced therein.