Thin film magnetic recording media

A thin film magnetic recording medium has a shape imparting substance disposed on a substrate, and a thin-film layer including at least a magnetic layer formed on the shape imparting substance. The area of each of the projecting portions of the thin-film layer which are formed by virtue of the shape imparting substance is set such as to be more than four times as large as the area of each of the particles of the shape imparting substance. The center line of each of the projecting portions of the thin-film layer may be made offset from the center line of the corresponding particle of the shape imparting substance. Thus, it is possible for the thin film magnetic recording medium to display excellent electromagnetic response properties and runability as well as durability even under a harsh environment.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to thin film magnetic recording media such as 
a magnetic tape and a magnetic disk. 
2. Description of the Prior Art 
Recently, thin film magnetic recording media have attracted interest as 
high-density magnetic recording media and have gradually been put into 
practical use. It is well known that thin film magnetic recording media 
display remarkably excellent electromagnetic response properties in 
high-density magnetic recording operations as compared with the coating 
type magnetic recording media which have heretofore been employed. 
However, it is still necessary for thin film magnetic recording media to 
be improved in their practical properties for the purpose of their 
practical application as high-density magnetic recording media. The 
required improvements in the practical properties of thin film magnetic 
recording media may be roughly classified as follows: 
(1) control of the surface configuration 
(2) improvements in the practical properties in terms of coating 
(3) improvements in quality of materials 
Among these, the present invention is concerned with the control of the 
surface configuration of thin film magnetic recording media. 
In high-density magnetic recording, losses in recording and reproducing 
operations as a result of spacing loss generally involve an extremely 
serious problem. For this reason, it is desired to improve the surface 
properties of thin film magnetic recording media. If the surface 
properties of thin film magnetic recording media are improved, however, 
although electromagnetic response properties are improved, runability and 
durability are impaired. Therefore, various surface configurations have 
been examined in order to improve the runability and durability as well as 
electromagnetic response properties. 
The following is a description of a conventional thin film magnetic 
recording medium. 
Referring to FIG. 1 which is a sectional view of a conventional thin film 
magnetic recording medium, the reference numeral 1 denotes a substrate, 2 
each of the particles of a shape imparting substance, 3 a thin-film layer 
which includes at least a magnetic layer, and 4 projecting portions of the 
thin-film layer 3. It is possible by this arrangement to improve the 
electromagnetic response properties together with the runability and 
durability of a thin film magnetic recording medium by employing the 
substrate 1 which has relatively excellent surface properties and 
controlling the surface properties of the medium by the use of the shape 
imparting substance 2, as shown in FIG. 1. The above-described 
arrangement, however, suffers from the following problem. Namely, under a 
normal environment such as at 23.degree. C. and 50% RH, the 
electromagnetic response properties, runability and durability of the 
medium are all satisfactory, but under a harsh environment such as at 
40.degree. and 95%RH, although the electromagnetic response properties and 
runability are still excellent, durability is not satisfactory. 
SUMMARY OF THE INVENTION 
In view of the above-described problem of the prior art, it is a primary 
object of the present invention to provide thin film magnetic recording 
media capable of displaying excellent electromagnetic response properties 
together with satisfactory runability and durability even under a harsh 
environment of, e.g., 40.degree. C. and 95%RH. 
To this end, the present invention provides a thin film magnetic recording 
medium having a shape imparting substance disposed on a substrate, and a 
thin-film layer including at least a magnetic layer formed on the shape 
imparting substance, wherein the area of each of the projecting portions 
of the thin-film layer which are formed by virtue of the shape imparting 
substance is more than four times as large as the area of each of the 
particles of the shape imparting substance, or wherein the center line of 
each of the projecting portions of the thin-film layer is not coincident 
with the center line of the corresponding particle of the shape imparting 
substance. 
By virtue of the above-described arrangement, it is possible for the thin 
film magnetic recording medium to display excellent electromagnetic 
response properties together with satisfactory runability and durability 
even under a harsh environment. 
The above and other objects, features and advantages of the present 
invention will become clear from the following description of the 
preferred embodiments thereof, taken in conjunction with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be described hereinunder through embodiments 
with reference to the accompanying drawings. 
Referring first to FIG. 2, which is a sectional view showing one example of 
the basic arrangement of the thin film magnetic recording medium in 
accordance with one embodiment of the present invention, the reference 
numeral 5 denotes a substrate, 6 particles of a shape imparting substance, 
7 a thin-film layer including at least a magnetic layer, and 8 projecting 
portions of the thin-film layer 7. 
By virtue of the shape imparting substance 6 disposed on the substrate 5, 
the surface of the thin-film layer 7 which includes at least a magnetic 
layer is formed with the projecting portions 8 each having an area four or 
more times as large as the area of each of the particles of the shape 
imparting substance 6 in the manner shown in FIG. 2. It is to be noted 
that the term "area" is herein employed to mean the horizontal cross 
sectional area of each of the particles of the shape imparting substance 6 
or each of the projecting portions 8 at the respective points thereof 
where their circumference is at its maximum. 
Referring next to FIG. 3, which is a sectional view showing another example 
of the basic arrangement of the thin film magnetic recording medium in 
accordance with another embodiment of the invention, the reference numeral 
9 represents a substrate, 10 each of the particles of a shape imparting 
substance, and 11 a thin-film layer including at least a magnetic layer. 
The shape imparting substance 10 which is disposed on the substrate 9 
causes the thin-film layer 11 to have projecting portions 12 on its 
surface. In this case, the center line 12a of each of the projecting 
portions 12 of the thin-film layer 11 is, as shown in FIG. 3, not 
coincident with the center line 10a of the corresponding particle of the 
shape imparting substance 10. 
The material for the substrates 5 and 9 may be properly selected from 
metals, oxides, nitrides and so forth. As to the shape imparting 
substances 6 and 10, it is possible to solely employ nuclei or particles 
of a material which is properly selected from oxides, nitrides, metals and 
other materials, or employ a combination of nuclei and a binder material. 
Each of the thin-film layers 7 and 11 is constituted by a single layer or 
a plurality of layers made of a material selected from metals, oxides and 
nitrides, or a mixture of materials selected therefrom, each thin-film 
layer including at least a magnetic layer. The method of forming the 
thin-film layers 7 and 11 is properly selected from sputtering, vacuum 
deposition, ion plating, deposition, coating and so forth. Each of the 
thin-film layers 7 and 11 may include an anti-corrosive agent, a 
lubricant, an abrasive, etc., in addition to the magnetic film. The 
surface roughness of the substrates 5 and 9 at the side thereof which is 
closer to the magnetic surface of the medium is preferably set at an 
average roughness of 1,000 .ANG. or less, more preferably 300 .ANG. or 
less. The particle diameter of the shape imparting substances 6 and 10 is 
preferably selected to fall between 20 .ANG. and 1,000 .ANG., more 
preferably between 40 .ANG. and 400 .ANG.. The particle distribution 
density of each of the shape imparting substances 6 and 10 is preferably 
0.1 to 1,000 particles per .mu.m.sup.2, more preferably 1 to 100 particles 
per .mu.m.sup.2. The film thickness of each of the thin-film layers 7 and 
11 is preferably selected to fall between 500 .ANG. and 5,000 .ANG., and 
the film thickness of the magneitc layer preferably between 500 .ANG. and 
2,000 .ANG.. 
There is a large difference in terms of the area between the respective 
projecting portions of the thin-film layers which are respectively shown 
in FIGS. 1 and 2. It is possible to vary the area of each of the 
projecting portions of the thin-film layer by controlling the conditions 
in which the thin-film layer is formed, such as, for example, an 
atmospheric gas, such as Ar or He, in vacuum deposition, ion plating or 
sputtering. 
It is conjectured that the thin film magnetic recording medium arranged as 
above involves a low packing factor in the vicinity of each of the 
particles of the shape imparting substance and therefore contains voids at 
such a portion. It is therefore surmised that the existence of such voids 
favorably reduces the magnitude of the stress transmitted to the substrate 
portion and consequently improves the durability of the thin film magnetic 
recording medium. 
Referring to FIGS. 1 and 3, in the arrangement shown in FIG. 1 each 
projecting portion 4 of the thin-film layer 3 is formed in symmetry with 
respect to the corresponding particle of the shape imparting substance 2, 
whereas in the arrangement shown in FIG. 3 each projecting portion 12 of 
the thin-film layer 11 is formed asymmetrical with respect to the 
corresponding particle of the shape imparting substance 10. It is possible 
to obtain such asymmetry by varying conditions for forming the thin-film 
layer, for example, by controlling an atmospheric gas, or properly 
selecting a deposition material, or employing a special evaporation source 
or heating treatment, in vacuum deposition, ion plating or sputtering. 
Referring next to FIG. 4 which is a plan view of the arrangement shown in 
FIG. 3, an offset angle .theta. is made between the longitudinal direction 
of the substrate 9 and an imaginary line connecting the center line of 
each of the particles of the shape imparting substance 10 and the 
corresponding projecting portion 12 of the thin-film layer 11. 
Further, although in the arrangement shown in FIG. 3 the area of each of 
the projecting portions 12 of the thin-film layer 11 is substantially 
equal to the area of each of the particles of the shape imparting 
substance 10, the present invention also includes such an arrangement as 
shown in FIG. 5 in which the area of each of the projecting portions 16 of 
a thin-film layer 15 is larger than the area of each of the particles of a 
shape imparting substance 14. When the area of each of the projecting 
portions 16 of the thin-film layer 15 is more than four times as large as 
the area of each of the particles of the shape imparting substance 14, the 
present invention offers a particularly remarkable effect. In FIG. 5, the 
reference numeral 13 denotes a substrate, 14 particles of a shape 
imparting substance, 15 a thin-film layer, 14a the center line of each of 
the particles of the shape imparting substance 14, and 16a the center line 
of each of the projecting portions 16 of the thin-film layer 15. 
It is possible to confirm the offset distance between the center line of 
each of the particles of the shape imparting substance and the center line 
of the corresponding projecting portion of the thin-film layer by 
observing the cross-section of the thin film magnetic recording medium 
with a scanning electron microscope. The measurement limit of the existent 
analyzing techniques is on the order of 100 .ANG. in terms of the 
above-described offset distance although it depends on the materials 
employed for the thin-film layer and the shape imparting substance. 
However, it has been confirmed that a sample which involves a center line 
offset distance of more than 100 .ANG. has improved durability, this being 
offered by the present invention. 
It is considered that the thin film magnetic recording medium arranged as 
above is asymmetric in the vicinity of each of the particles of the shape 
imparting substance and, therefore, the stress concentration which takes 
place when force acts on the surface of the projecting portions of the 
thin-film layer has a greatly intensified factor of asymmetry. For this 
reason, although the thin film magnetic recording medium which has the 
symmetric projecting portions, such as that shown in FIG. 1, has a 
durability which is constant when the medium is caused to travel in any 
direction, the thin film magnetic recording medium according to the 
invention, such as that shown in FIG. 3, has a durability which greatly 
differs depending on the travelling direction. It is therefore conjectured 
that it is possible to obtain even better durability by selecting a 
specific travelling direction. 
Further, the effect offered by the arrangement shown in FIG. 2 and the 
effect offered by the arrangement shown in FIG. 3 are independent from 
each other. Therefore, if these effects are simultaneously employed, it is 
possible to obtain a greater effect by virtue of synergism. 
The following is a description of more practical embodiments of the present 
invention. 
Embodiment 1: 
As the substrate, a polyethylene terephthalate substrate was employed 
having a thickness of 12 .mu.m and an average surface roughness of 50 
.ANG. on the side thereof which was closer to the magnetic surface of the 
medium. As the shape imparting substance, SiO.sub.2 particles with an 
average particle diameter of 150 .ANG. and Baylon resin were mixed in 
isopropyl alcohol and applied to the surface of the substrate. The density 
of the SiO.sub.2 particles in the mixed solution was 200 ppm, while the 
density of the Baylon resin was 100 ppm, and the particle density of the 
thus formed shape imparting substance was about 40 particles per 
.mu.m.sup.2. Then, while the substrate was being run along a cylindrical 
can with a diameter of 500 mm, CoNi (20wt %) was deposited on the surface 
of the substrate coated with the shape imparting substance up to a minimum 
incident angle of 40.degree. from the tangential direction at a substrate 
travelling speed of 20 m/min. In order to obtain proper magnetic 
properties, oxygen gas was introduced, and the degree of vacuum in the 
vicinity of the deposition portion was maintained at 1 to 
2.times.10.sup.-3 Pa. While doing so, a magnetic layer with a film 
thickness of 1,800 .ANG. was formed, and a sample A was thus obtained. 
Then, in addition to the above-described conditions, Ar gas was introduced 
in the vicinity of the deposition portion in the tangential direction and 
at various flow rates, that is, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 Nl/min, 
thereby samples B, C, D, E, F and G were obtained. Each of the samples was 
provided with a back coat layer and coated with a fluorine lubricant at 
the side of the sample which was closer to the magnetic layer. Then, the 
durability of the samples was measured by employing a deck with a rotary 
cylinder in an environment of 40.degree. C. and 95%RH FIG. 6 shows the 
respective relative durabilities of the samples with respect to the 
durability of the sample A. Further, the respective surface conditions of 
the samples were observed by means of a scanning electron microscope. This 
observation showed that the projecting portions of the thin-film layer 
formed by virtue of the shape imparting substance employing SiO.sub.2 as 
nuclei were substantially circular. The average diameter of the projecting 
portions of the thin-film layer of each sample was measured, and an 
average area of the projecting portions was obtained from the measured 
value. The relationship between the average area and the relative 
durability at 40.degree. and 95%RH is shown in FIG. 6. When each of the 
samples A to G was tested on a magnetic recording and reproducing 
apparatus having a rotary cylinder with a ferrite head at a relative speed 
between the tape and the head of 4 m/sec. and at a recording frequency of 
5 MHz, the output difference between the samples was within 1 dB, which 
was within the range of allowable measuring errors, and the respective 
electromagnetic response properties of the samples were substantially 
equal to each other. In addition, the respective initial runability of the 
samples under various environments were substantially equal to each other. 
As will be clear from FIG. 6, when the average area of the projecting 
portions of the thin-film layer is more than four times as large as the 
area of each of the particles of the shape imparting substance, the 
durability of the thin film magnetic recording medium under an environment 
at 40.degree. and 95%RH is improved. If the average area of the projecting 
portions of the thin-film layer is more than ten times as large as the 
area of each of the particles of the shape imparting substance, then the 
durability is improved by a large margin. 
As described above, it is possible according to this embodiment to improve 
the durability of the thin film magnetic recording medium while satisfying 
the requirements for electromagnetic response properties and runability 
provided that the average area of the projecting portions of the thin-film 
layer is more than four times as large as the area of each of the 
particles of the shape imparting substance. 
Embodiment 2: 
As the substrate, a polyethylene terephthalate substrate was employed 
having a thickness of 8 .mu.m and an average surface roughness of 120 
.ANG. on the side thereof which was closer to the magnetic surface of the 
medium. As the shape imparting substance, polysulfone particles having an 
average particle diameter of 200 .ANG. and a polyurethane resin were mixed 
in methyl alcohol and applied to the surface of the substrate. The 
particle density of the shape imparting substance was set at about 10 
particles per .mu.m.sup.2. Then, deposition was made by employing a 
deposition apparatus having a heating source adapted to effect heating 
from one side of the apparatus, such as that shown in FIG. 7. In the 
Figure, the reference numeral 17 denotes an evaporation source which is 
capable of containing a deposition material, 18 a molybdenum heater, 19 a 
mask, 20 a water-cooled can with a diameter of 500 mm, 21 a supply shaft, 
and 22 a take-up shaft. With Pb employed as the deposition material, a Pb 
thin-film layer with a thickness of 1,000 .ANG. was deposited on the 
surface of the substrate coated with the shape imparting substance by 
means of electron beam heating at a substrate travelling speed of 30 
m/min. During the deposition, the molybdenum heater 18 was supplied with a 
current of 50 A at 10 V, thereby it was possible to offset from each other 
the center line of each of the particles of the shape imparting substance 
and the center line of the corresponding projecting portion of the Pb 
thin-film layer. The center line of each of the projecting portions of the 
Pb thin-film layer was offset from the center line of the corresponding 
particle of the shape imparting substance in the opposite direction 
relative to the heating source constituted by the molybdenum heater 18. 
Various samples were prepared by varying the position of the molybdenum 
heater 18 such that the angle .theta. (corresponding to the angle .theta. 
shown in FIG. 4) made between the substrate travelling direction and an 
imaginary line connecting between the center line of each of the 
projecting portions of the Pb thin-film layer and the center line of the 
corresponding particle of the shape imparting substance had various 
values, that is, .theta.=0.degree., 30.degree., 60.degree., 90.degree., 
120.degree., 150.degree. and 180.degree.. Then, with these samples 
employed, CoNi (10 wt %) was deposited up to a minimum incident angle of 
40.degree. from the tangential direction along the water-cooled can with a 
diameter of 500 mm. In order to obtain proper magnetic properties, oxygen 
gas was introduced during the deposition. Consequently, the degree of 
vacuum during the deposition was 2 to 3.times.10.sup.-3 Pa, and the film 
thickness of the thus formed magnetic layer was about 1,500 .ANG.. These 
magnetic tapes were observed by employing a scanning electron microscope. 
The observation showed that the area of each of the projecting portions of 
the magnetic layer of each of the tapes was about eight times as large as 
the area of each of the particles of the shape imparting substance. 
Further, sputter etching was stepwisely effected from the magnetic layer 
surface side of each of the samples, and observation was carried out for 
every step of the etching with the scanning electron microscope. The 
observation showed that the offset distance between the center line of 
each of the particles of the shape imparting substance and the center line 
of the corresponding projecting portion of the thin-film layer was about 
500 .ANG. for all the samples, and it was confirmed that the offset angles 
.theta. between those center lines in relation to the samples were 
respectively 0.degree., 30.degree., 60.degree., 90.degree., 120.degree., 
150.degree. and 180.degree. as described above. 
The respective surfaces of these samples were coated with a lubricant, and 
the samples were evaluated in terms of relative durability under an 
environment of 40.degree. C. and 95%RH by employing a magnetic recording 
and reproducing apparatus having a rotary cylinder with a diameter of 40 
mm. The magnetic tape employed as the reference for the evaluation was 
prepared such as to possess an arrangement similar to those of the other 
magnetic tapes but was not subjected to heating by means of the molybdenum 
heater 18 at the time of forming the Pb thin-film layer; therefore, in the 
reference magnetic tape, as shown in FIG. 1, the center line of each of 
the particles of the shape imparting substance was coincident with the 
center line of the corresponding projecting portion of the thin-film layer 
and the size of each projecting portion was substantially equal to that of 
each particle of the shape imparting substance. FIG. 8 shows the 
relationship between the offset angle .theta. and the relative durability 
of each of the samples at 40.degree. and 95%RH, the offset angle 8 being 
made between the magnetic tape travelling direction and an imaginary line 
connecting between the center line of each of the particles of the shape 
imparting substance and the center line of the corresponding projecting 
portion of the thin-film layer. It is to be noted that the offset angle 
.theta. of 0.degree. on the axis of abscissa in the graph shown in FIG. 8 
exhibits that the magnetic head moves toward the center line of each of 
the particles of the shape imparting substance from the center line of the 
corresponding projecting portion of the thin-film layer, while the offset 
angle .theta. of 180.degree. on the abscissa axis exhibits that the 
magnetic head moves in the opposite direction relative to the above. As 
will be clear from FIG. 8, in the case of a magnetic tape in which the 
center line of each of the particles of the shape imparting substance is 
not coincident with the center line of the corresponding projecting 
portion of the thin-film layer, it is possible to improve its durability 
even under a severe environment such as at 40.degree. and 95%RH by 
properly selecting the travelling direction of the magnetic tape. It is to 
be noted that each of the reference and sample magnetic tapes was 
subjected to recording and reproducing operations at a recording 
wavelength 0.7 .mu.m by employing a ferrite head. The testing showed that 
the reproduction output difference between the tapes was within 1 dB, 
which was within the range of allowable measuring errors, and the 
respective electromagnetic response properties of the tapes were 
substantially equal to each other, while their respective initial 
runability under various environments were also substantially equal to 
each other. 
As described above, it is possible according to this embodiment to improve 
the durability of the thin film magnetic recording medium while satisfying 
the requirements for electromagnetic response properties and runability by 
arranging the medium such that the area of each of the projecting portions 
of the thin-film layer is more than four times as large as the area of 
each of the particles of the shape imparting substance and the center line 
of each of the particles of the shape imparting substance is made offset 
from the center line of the corresponding projecting portion of the 
thin-film layer. 
Embodiment 3: 
As the substrate, a polyethylene terephthalate substrate was employed 
having a thickness of 7 .mu.m and an average surface roughness of 60 .ANG. 
on the side thereof which was closer to the magnetic surface of the 
medium. As the shape imparting substance, SiO.sub.2 particles with an 
average particle diameter of 80 .ANG. was mixed with Baylon resin and 
applied to the surface of the substrate at a particle density of about 20 
particles per .mu.m.sup.2. Then, CoCr (20 wt %) with a film thickness of 
5,000 .ANG. was deposited on the surface of the substrate coated with the 
shape imparting substance in an AR gas atmosphere by employing a 
deposition apparatus such as that shown in FIG. 9. In the Figure, the 
reference numeral 23 denotes an evaporation source, 24 a mask, 25 an Ar 
gas inlet, 26 a water-cooled cylindrical can, 27 a supply shaft, and 28 a 
take-up shaft. The Ar gas was sidewardly blown in the vicinity of the 
deposition portion from a nozzle of 0.3 mm in diameter at the distal end 
of the Ar gas inlet 25 at various flow rates, that is, 0, 0.2, 0.4 and 0.6 
Nl/min., whereby magnetic tapes H, I, J and K were obtained. The 
respective relative durabilities of the magnetic tapes under an 
environment of 40.degree. and 95%RH were evaluated with respect to the 
durability of the magnetic tape H. Further, the cross-section of each of 
the magnetic tapes was observed by employing a scanning electron 
microscope so as to measure the offset distance between the center line of 
each of the particles of the shape imparting substance and the center line 
of the corresponding projecting portion of the thin-film layer. FIG. 10 
shows the relationship between the offset distance between the 
above-described center lines and the durability of each of the magnetic 
tapes under an environment of 40.degree. and 95%RH. In this case, the area 
of each of the projecting portions of the thin-film layer was slightly 
larger than the area of each of the particles of the shape imparting 
substance, but the former was two or less times as large as the latter. As 
will be clear from FIG. 10, by virtue of the arrangement in which the 
center line of each of the particles of the shape imparting substance is 
not coincident with the center line of the corresponding projecting 
portion of the thin-film layer, the durability of the magnetic tape under 
an environment of 40.degree. and 95%RH is greatly improved. It is to be 
noted that the examination of the respective recording and reproducing 
characteristics of the magnetic tapes H, I, J and K at a recording 
wavelength of 0.7 .mu.m by the use of an amorphous head showed that the 
reproduction output difference between the tapes was within 1 dB, which is 
within the range of allowable measuring errors, and their electromagnetic 
response properties were substantially equal to each other, and 
furthermore the respective initial runability of the tapes under various 
environments were also substantially equal to each other. 
As described above, according to this embodiment in which the center line 
of each of the particles of the shape imparting substance is made offset 
from the center line of the corresponding portion of the thin-film layer, 
it is possible to improve the durability of the thin film magnetic 
recording medium while satisfying the requirements for electromagnetic 
response properties and runability. 
Embodiment 4: 
As the substrate, an aromatic polyimide substrate was employed having a 
thickness of 30 .mu.m and an average surface roughness of 70 .ANG. at the 
side thereof which was closer to the magnetic layer of the medium. As the 
shape imparting substance, SiO.sub.2 with an average particle diameter of 
60 .ANG. was mixed with an epoxy resin and applied to the surface of the 
substrate at a particle density of about 10 particles per .mu.m.sup.2. 
Then, Zn with a film thickness of 2,000 .ANG. was deposited on the surface 
of the substrate coated with the shape imparting substance by employing a 
deposition apparatus such as that shown in FIG. 7 which gradually increase 
the thickness of the film. Further, an .alpha.-Fe.sub.2 O.sub.3 layer 
containing 1.5% of Cu, 1% of Ti and 3% of Co was formed on the Zn to a 
thickness of 1,500 .ANG. by sputtering in an oxygen atmosphere and was 
then reduced to Fe.sub.3 O.sub.4 at 240.degree.. The surface of the thus 
prepared sample was coated with a lubricant and formed into the shape of a 
floppy disk with a diameter of 3 inches. The evaluation of the durability 
of this disk under an environment of 40.degree. and 95%RH showed that the 
disk displayed excellent durability without any abnormality occurring 
during the testing in which the disk was subjected to contact-start-stop 
operations a total of 500 times. 
The analysis of the above-described sample by the use of a scanning 
electron microscope showed that each of the projecting portions of the 
thin-film layer had a shape with appropriate directional properties, and 
the area of each of the projecting portions of the thin-film layer was 
more than ten times as large as the area of each of the particles of the 
shape imparting substance, and further the offset distance between the 
center line of each of the projecting portions of the thin-film layer and 
the center line of the corresponding particle of the shape imparting 
substance was about 200 .ANG.. 
Embodiment 5: 
As the substrate, a polyethylene terephthalate substrate was employed 
having a thickness of 10 .mu.m and an average surface roughness of 40 
.ANG. on the side thereof which was closer to the magnetic surface of the 
medium, and as a ground treatment layer, a titanium film with an average 
film thickness of 200 .ANG. was formed on the substrate by vacuum 
deposition. On the titanium layer was disposed carbon black with an 
average particle diameter of 100 .ANG. by means of coating at a particle 
density of 20 particles per .mu.m.sup.2. Further, CoNi (20 wt %) was 
deposited on the carbon black up to a minimum incident angle of 50.degree. 
from the tangential direction along a can with a diameter of 800 mm. 
During the deposition, oxygen and Ar were introduced at respective flow 
rates of 0.5 Nl/min. and 0.3 Nl/min., and ion plating was carried out at a 
degree of vacuum of 1.3.times.10.sup.-3 Pa. As a result, each of the 
projecting portions thus formed at the surface of the CoNi layer had a 
shape with appropriate directional properties. The area of each of the 
projecting portions of the thin-film layer was more than 20 times as large 
as the area of each of the particles of the shape imparting substance. 
Further, the offset distance between the center line of each of the 
projecting portions of the thin-film layer and the center line of the 
corresponding particle of the shape imparting substance was 100 to 200 
.ANG.. A back coat layer was provided on the surface of this sample 
opposite to its magnetic surface, while a fluorine plasma polymerization 
film was formed on the magnetic surface, thereby forming a magnetic tape. 
The travelability of this magnetic tape was evaluated under an environment 
of 40.degree. and 95%RH by employing a rotary cylinder type VTR. The 
evaluation showed that the magnetic tape displayed stable runability 
without causing any output fluctuation even after it had been run 100 
times. Thus, it was found that the magnetic tape had satisfactory 
durability. 
Embodiment 6: 
Polyethylene terephthalate was coated with SiO.sub.2 particles contained in 
a binder and was then subjected to drawing. The polyethylene terephthalate 
substrate thus formed had SiO.sub.2 particles with an average particle 
diameter of 120 .ANG. disposed on its surface at a particle density of 
five particles per .mu.m.sup.2. This sample was further provided with a 
CoNi layer, a back coat layer and a plasma polymerization layer in the 
manner shown in Embodiment 5, whereby the sample displayed satisfactory 
durability substantially equal to that of Embodiment 5. 
It is to be noted that, although in the above-described embodiments 
practical effects have been shown in regard to six kinds of material, it 
has been confirmed that it is also possible for the thin film magnetic 
recording medium according to the present invention to obtain similar 
effects with other combinations of the above-described materials which 
constitute the described embodiments, or other magnetic materials. 
As has been described above, the thin film magnetic recording medium 
according to the present invention has a shape imparting substance 
disposed on a substrate, and a thin-film layer formed on the shape 
imparting substance and including at least a magnetic layer, wherein the 
area of each of the projecting portions of the thin-film layer which are 
formed by virtue of the shape imparting substance is more than four times 
as large as the area of each of the particles of the shape imparting 
substance, or wherein the center line of each of the projecting portions 
of the thin-film layer which are formed by virtue of the shape imparting 
substance is made offset from the center line of the corresponding 
particle of the shape imparting substance. By virtue of this arrangement, 
it is possible to provide a thin film magnetic recording medium which 
displayes excellent electromagnetic response properties and runability as 
well as durability even under a severe environment. Thus, the present 
invention offers great practical effects. 
Although the invention has been described through specific terms, it is to 
be noted here that the described embodiments are not exclusive and various 
changes and modifications may be imparted thereto without departing from 
the scope of the invention which is limited solely by the appended claims.