Magnetic recording system

A magnetic recording system for recording signals onto coat-type magnetic tape using magnetic powder by using a magnetic head, and a magnetic recording system for recording signals onto a coat-type magnetic disk using magnetic powder by running magnetic head in contact with the disk, are disclosed. The magnetic tape has a coercive force Hc of 2000 to 3800 Oe in the former system, while the magnetic disk has a coercive force He of 2000 to 3500 Oe in the latter system. In both systems, signals are recorded by using a magnetic head using magnetic core members having a saturation magnetic flux density of 15 kG or greater. The magnetic core member having the saturation magnetic Flux density of 15 kG or greater is exemplified by a material expressed by a composition formula (Fe.sub.95.5 Al.sub.1 V.sub.0.5 Nb.sub.0.5 Cu.sub.0.5 Ru.sub.2).sub.92 N.sub.6 O.sub.2.

BACKGROUND OF THE INVENTION 
This invention relates to a magnetic recording system for writing various 
information signals onto a magnetic tape or a magnetic disk, and 
particularly to a novel magnetic recording system to realize high 
recording density and high reliability. 
In the recording system using the magnetic tape, the combination of the 
magnetic tape and the magnetic head has evolved in the order of a 
.gamma.-Fe.sub.2 O.sub.3 coat-type tape and a ferrite head, CrO.sub.2 and 
a ferrite head, Co-.gamma.-Fe.sub.2 O.sub.3 and a ferrite head, metallic 
powder and a sendust head or amorphous head, and a CoNi evaporation tape 
and a sendust head or amorphous head, to achieve high density magnetic 
recording. 
This evolution depends largely upon evolution of the magnetic recording 
medium. Stated differently, as the coercive force and the residual 
magnetic flux density of the magnetic recording medium have increased, 
reproduction output in a shorter wavelength region is improved. Thus, 
higher density is achieved. 
As a novel recording system, a combination of a Co-Cr vertical magnetic 
recording medium and a vertical magnetic head, or a combination of a ring 
head and a Co-O vertical magnetic recording medium, is proposed as in the 
79th Studies of Japan Applied Magnetics Institute, Reference 79-2, pages 9 
to 16. 
However, any of the above combinations has a problem in the rubbing surface 
between the magnetic tape and the magnetic head. The rubbing surface 
between the magnetic tape and the magnetic head does not exhibit 
satisfactory durability and is damaged by the medium. 
Thus, the vertical magnetic recording using Co-Cr and the like has not 
overcome the problem in reliability for the novel magnetic recording 
medium. 
Meanwhile, an attempt to raise the coercive force Hc of the magnetic tape 
in an in-plane medium is described in the 79th Studies of Japan Applied 
Magnetics Institute, Reference 79-2, page 15, from line 9, as follows: "By 
arraying acicular particles of an average coercive force of approximately 
3000 Oe having similar particle diameter and size, densely and without 
having magnetic interaction in the longitudinal direction to have a 
thickness of tens of rim, information can be written with ultra high 
resolution of 10,000 bits/mm or higher with a bit interval of 100 nm or 
smaller." 
However, the higher coercive force of the medium is limited by writing 
capability of the magnetic head. 
A recording system using a magnetic head having a magnetic core composed of 
sendust or Co based amorphous has been conventionally employed, while it 
has not been conceived to raise the coercive force of the coat-type tape 
to 2000 Oe or higher in the magnetic recording system capable of recording 
and reproduction. 
This is partly because the study in the field of the novel magnetic 
recording system is now on the Co based evaporation tape or the Co-Cr 
vertical magnetic recording, as seen from the above-mentioned reference 
publication. The coat-type medium is studied simply for lower costs and 
higher reliability, not for research and development of ultra high 
recording density media. 
As described above, the study for more than a decade on the vertical 
magnetic recording system has not brought it to the stage of practical 
application to replace the Co based evaporation tape. A highly reliable 
magnetic recording system for a higher density has not been proposed since 
practical application of the Co based evaporation tape in 1989. 
Since high resolution of TV picture as represented by HD-VTR increases 
information to be recorded, development of a magnetic recording system 
capable of recording with a higher density to replace the Co based 
evaporation tape is desired. 
OBJECT AND SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a magnetic 
recording system capable of achieving high density recording and having 
high output and reliability. 
According to the present invention, there is provided a magnetic recording 
system employing a coat-type magnetic tape using magnetic powder. The 
magnetic recording system has a magnetic tape having a coercive force Hc 
of 2000 to 3300 Oe, and a magnetic head using magnetic core members having 
a saturation magnetic flux density of 15 kG and greater for recording 
signals. According to the present invention, there is also provided a 
contact-type magnetic recording system employing a coat-type magnetic disk 
using magnetic powder. The magnetic recording system has a magnetic disk 
having a coercive force Hc of 2000 to 3500 Oe, and a magnetic head using 
magnetic core members having a saturation magnetic flux density of 15 kG 
for recording signals. 
Thus, by using the coat-type magnetic media of extremely high coercive 
force and the magnetic head using the magnetic core members of high 
saturation magnetic flux density for recording, it is possible to secure 
sufficient reliability and achieve recording with higher density than that 
of the evaporation tape, which has been capable of recording with higher 
density than any other conventional tape contact-type magnetic recording 
system. 
Since the magnetic recording system of the present invention uses the 
coat-type tape having high durability, the problem of rubbing between the 
tape and the head in the vertical magnetic recording system using the 
Co-Cr medium can be solved. 
Also, the magnetic recording system of the present invention uses the 
magnetic core member having high saturation magnetic flux density for 
recording, recording in an MP tape having a large coercive force Hc can be 
achieved, and reproduction output exceeding that of an ME tape can be 
produced. Consequently, high density magnetic recording of a great amount 
of information as in HD-VTR can be realized.

DETAILED DESCRIPTION OF THE INVENTION 
In the present invention, signals are first recorded by a magnetic head 
using magnetic core members having a saturation magnetic flux density of 
15 kG or greater. Conventionally, a high Hc region of 1700 Oe or higher 
has not conceived because of limitation of the recording head. However, as 
proposed by the present Applicant, magnetic core members exhibiting a 
saturation magnetic flux density Bs of 19 kG or greater, which is nearly 
twice that of the conventional sendust, and having sufficiently high 
corrosion resistance and wear resistance, are available. Thus, the high Hc 
region can be conceived, and superiority of the coat-type magnetic tape 
using metallic powder, hereinafter referred to as an MP tape, is now made 
apparent. 
As the magnetic core member used in the present invention, any magnetic 
core member having the saturation magnetic flux density of 15 kG as 
described above can be used. For instance, an alloy material expressed by 
a composition formula (Fe.sub.a M.sub.b Cu.sub.c Ru.sub.d).sub.e N.sub.f 
O.sub.g, with a, b, c, d, e, f, g expressing the composition by atomic 
percentage, and M representing at least one of Si, Al, Ta, B, Mg, Ca, St, 
Cr, Mn, Zr, Nb, Ti, Mo, V, W, Hf, Ga, Ge and rare earth elements. The 
composition range is as follows: 
0.1.ltoreq.b.ltoreq.5 
0.ltoreq.c.ltoreq.8 
0&lt;d.ltoreq.5 
0.2.ltoreq.c+d.ltoreq.8 
a+b+c+d=100 
0.5.ltoreq.f.ltoreq.15 
0.1.ltoreq.g.ltoreq.13 
e+f+g=100 
The additional element M may be a combination of M.sup.I as at least one of 
Al, Ga, Ti and rare earth group, and M.sup.II as at least one of Nb, Ta, 
V, Ze, Hr. In this case, the material is expressed by a composition 
formula (Fe.sub.a M.sup.I.sub.j M.sup.II.sub.k Cu.sub.c Ru.sub.d).sub.e 
N.sub.f O.sub.g. The composition range is as follows: 
0.1.ltoreq.j.ltoreq.2.5 
0.15.ltoreq.k.ltoreq.2.5 
0.ltoreq.c.ltoreq.8 
0&lt;d.ltoreq.5 
0.2.ltoreq.c+d.ltoreq.8 
a+j+k+c+d=100 
0.5.ltoreq.f.ltoreq.15 
0.1.ltoreq.g.ltoreq.13 
e+f+g=100 
Meanwhile, a magnetic flux density 6 to 7 times greater than the coercive 
force Hc of the magnetic tape is conventionally required for the magnetic 
core member of the recording head. In the case of the magnetic tape of 
coercive force Hc, the saturation magnetic flux density Bs of the magnetic 
core member is 12 to 14 kG for the magnetic tape having a coercive force 
Hc of 2000 Oe, while the magnetic tape capable of recording the magnetic 
head using the magnetic core member having a saturation magnetic flux 
density Bs of 19 to 20 kG has a coercive force Hc of approximately 3000 
Oe. 
The magnetic powder may have a coercive force of approximately 3500 Oe 
through improvement in acicular ratio of particles and diminution of the 
surface oxidation layer. However, it is preferred to set the coercive 
force Hc of the magnetic tape to 2000 to 3000 Oe because of the limitation 
on the side of the magnetic head as described above. Although the 
description is mainly of the magnetic tape so far, the same can be true of 
the contact-type magnetic disk such as a floppy disk. 
In the present invention, since the coat-type magnetic recording medium 
having high durability is used, the problem in durability as pointed out 
in the vertical recording is eliminated. 
Also, the superiority in reproduction output of the coat-type magnetic 
recording medium to that of the conventional Co based evaporation tape 
will be later described. 
The coat-type magnetic recording medium, particularly a metal tape (MP 
tape) for high density magnetic recording, employs a recording medium 
composed of fine particles of Fe-Co alloy consisting mainly of Fe. In this 
case, the crystal magnetic anisotropy of the magnetic alloy is low, and 
the large coercive force is caused by anisotropy in shape of the acicular 
particles. With the anisotropy in shape, the coercive force increases as 
the acicular ratio increases or as magnetization increases. If the 
magnetization of the particles increases by thinning the surface oxidation 
layer of the magnetic powder, the coercive force increases. The magnitude 
of magnetization and the coercive force are in conformity with each other 
for improving properties. 
In the Co based evaporation tape, the crystal magnetic anisotropy of the Co 
based alloy causes the coercive force. The crystal is isolated and 
diminished to introduce a large coercive force. An inclined evaporation 
method is used to isolate the crystal, and oxygen is introduced to produce 
finer crystals. In order to raise the coercive force, it is necessary to 
increase the amount of oxygen introduced to produce finer Co based crystal 
grains. However, as described in the 79th Studies of Japan Applied 
Magnetics Institute, Reference 79-5, page 33, the introduction of oxygen 
increases the surface oxidation layer of Co particles or the gap between 
Co particles, and lowers the magnetization. In short, in the ME tape, a 
greater coercive force lowers tape magnetization. 
The capability of recording information onto the magnetic tape with a high 
density is expressed by performance indices (.delta.MrHc).sup.0.6 and 
(.delta.Mr/Hc).sup.-0.4 with .delta. denoting the film thickness and Mr 
denoting the residual magnetic flux density of the tape, as described in 
the 79th Studies of Japan Applied Magnetics Institute, Reference 79-2, 
page 14. The index (.delta.MrHc).sup.0.6 is proportional to the residual 
magnetic flux density of the tape surface with a low density, while the 
index (.delta.Mr/Hc).sup.-0.4 is proportional to the recording density for 
halving the residual magnetic flux density. That is, it is preferred that 
both indices are at large values. 
FIGS. 1 and 2 show graphs in which the coercive forces Hc, as parameters, 
of an ME tape (CoNi-O) and an MP tape (Br:2500 G) are plotted. The 
thickness of the magnetic layer differs between 2000 .ANG. in the ME tape 
and 3 .mu.m in the MP tape. However, the effective recording thickness is 
set to 1/4 of the recording wavelength. With a recording wavelength of 
0.5 .mu.m, both tapes have the same effective recording thickness. 
Therefore, the thickness .delta. is negligible. Mr and Br denote the same 
residual magnetic flux density. The index (.delta.Mr/Hc).sup.-0.4 exhibits 
a higher value in the MP tape in the entire region, because of the 
relatively low Br in comparison to Hc of the MP tape. 
Hr.times.Br is superior in the ME (evaporation) tape with the current 
coercive force Hc of approximately 1500 Oe. The difference in Hr.times.Br 
expressed by dB is approximately 5 dB, which substantially corresponds to 
the output difference between the ME tape and the MP tape. With the 
current coercive force Hc, the ME tape produces superior reproduction 
output. However, with a higher Hc, the magnetization of the ME tape is 
lowered, deteriorating Hc.times.Br as shown in FIG. 1. In the case of the 
MP tape, high Hc and high Br are in conformity with each other as 
described above, and Br can be maintained substantially at a constant 
level even with higher Hc. Consequently, in the high Hc region of 2000 Oe, 
the MP tape exceeds the ME tape in the maximum value, producing high 
reproduction output. 
This is not true of a non-contact type magnetic disk such as a hard disk. 
The medium producing conditions of the non-contact type magnetic disk 
differ from those of the contact-type magnetic disk, and recording media 
of high Hr and high Br can be easily produced. 
A preferred embodiment of the present invention will now be described in 
detail with reference to the drawings and experiment results. 
First, a magnetic head used in the present embodiment is described. For the 
magnetic core member, an alloy material having a composition (Fe.sub.95.5 
Al.sub.1 V.sub.0.5 Nb.sub.0.5 Cu.sub.0.5 Ru.sub.2).sub.92 N.sub.6 O.sub.2, 
with the numerical values expressing the composition by atomic percentage, 
was used. The alloy material had a saturation magnetic flux density Bs was 
19 to 20 kG. The alloy material and the insulating layer composed of 
SiO.sub.2 were stacked with a thickness of 3 .mu.m each, to form a 
hierarchical structure. Thus, a laminate-type head was produced. The 
laminate head is shown in FIG. 3. 
The magnetic head has magnetic core halves I, II composed of magnetic core 
members 1, 2 sandwiched by guard members 3 and 4, and guard members 5 and 
6, respectively. The magnetic core half I has a winding groove 7 formed 
therein. The magnetic core halves I, II are abutted to each other via a 
gap member, with end surfaces of the magnetic core members 1, 2 abutted to 
each other. The magnetic core halves I, II are bonded into one unit to 
form a magnetic gap g. 
A recording/reproduction test for various magnetic tapes of different 
coercive forces, that is, MP tapes and ME tapes, was conducted by using 
the laminate head, with a relative speed between the magnetic tape and the 
magnetic head of 3.8 m/second, a gap length of the magnetic head of 0.2 
.mu.m, and a recording frequency of 7 MHz. Results are shown in FIG. 4. In 
FIG. 4, lines A to F show characteristics of an MP tape with a coercive 
force Hc=3000 Oe, an MP tape with Hc=2500 Oe, an ME tape with Hc=1400 Oe, 
an MP tape with Hc=2000 Oe, an ME tape with Hc=1700 Oe, and an MP tape 
with Hc=1500 Oe, respectively. 
With Hc of approximately 1500 Oe, the ME tape is highly superior to the MP 
tape. The MP tape with Hc=2000 Oe has the maximum value close to that of 
the ME tape. In consideration of properties such as durability, the MP 
tape of Hc=2000 Oe is preferred. With a higher coercive force Hc, the MP 
tape has superior reproduction output. The above test, which cannot be 
carried out by using the conventional magnetic head, can be carried out 
for the first time by using the magnetic head employing the magnetic core 
members having a high saturation magnetic flux density. 
As the same test as in the magnetic tapes was carried out using a coat-type 
floppy disk and an evaporation disk, the perfectly same result was 
obtained.