JPH0321966B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-density, high-resolution magnetic recording medium.

In recent years, with the advancement of magnetic recording technology, high density,
High resolution is desired, and as compact VTRs, camera-integrated VTRs, and PCM compatible recorders are proposed, new magnetic recording media for use in these devices are needed.

Under these circumstances, thin film magnetic recording media using vacuum technology are attracting attention. Among these, methods for forming magnetic recording media by directly forming a ferromagnetic layer on a nonmagnetic substrate by vapor deposition, ion plating, sputtering, etc. are being extensively researched for practical use.

However, there are various characteristics that should be considered when designing the vapor-deposited tape for use as an audio tape, and surface electrical resistance, stiffness, etc. are important items. Regarding electrical resistance, since the magnetic layer of coated magnetic tape is mainly made of iron oxide and a polymer binder, the electrical resistance is 10 ⁹
It had reached a high value of Ω or more. For this reason, the main reason why the electrical resistance value becomes a problem is that the electrical charge generated in various places during running is difficult to escape from the tape, and it overlaps with the audio signal as so-called leftover noise, causing a harshness to the ears. To solve this problem, techniques have been put into practical use that lower the electrical resistance of the tape as a whole, such as by mixing a conductive material with the magnetic paint or by providing a conductive thin film on the back of the base.

However, in the case of vapor-deposited tapes, etc., the magnetic layer is made of metal or alloy and does not contain a polymeric binder, so the electrical resistance is extremely low, which causes problems when recording on decks with poor sealing around the head. may occur. In other words, when a tape with extremely low electrical resistance is used in a so-called three-head type deck, the circuit between the erasing head, recording head, and playback head is affected by the bias magnetic field generated by the recording head and the bias magnetic field from the erasing head. It has been found that the erase field induces noise in the read head.

This phenomenon is described, for example, in Japanese Patent Application Laid-Open No. 56-47924.
This is also disclosed in the publication No. Therefore, it is believed that most of the above-mentioned problems can be avoided if consideration is given when manufacturing the deck, but improvements are also desired from the viewpoint of manufacturing magnetic tapes. Furthermore, much of the above-mentioned noise can be reduced by increasing the electrical resistance of the magnetic tape surface, and one solution to this problem is to use a continuum as disclosed in the aforementioned Japanese Patent Application Laid-Open No. 56-47924. It has been proposed to create a partially discontinuous insulating layer by creating cracks in a thin magnetic layer, but even if it is somewhat effective, there is no technology to continuously form cracks in a thin magnetic layer with good reproducibility. It is extremely difficult. Furthermore, in vapor-deposited tapes, the thin magnetic layer of vapor-deposited metal or alloy tends to warp due to internal stress, and there is room for improvement in adhesion to the tape substrate (base film).

This invention was made in view of the above-mentioned circumstances, and includes: a non-magnetic substrate; a non-magnetic intermediate layer formed on the non-magnetic substrate; Submit a magnetic recording medium consisting of a magnetic layer which is an alternate stack of ferromagnetic layers and oxide layers obtained by oxidizing the ferromagnetic material constituting each ferromagnetic layer; A magnetic recording medium made of a magnetic oxide can have a high surface electrical resistance, improve noise, and have excellent electromagnetic conversion characteristics.
Furthermore, the intermediate layer is made of aluminum (Al), SiO _x (x
= 1.0 to 2.0) or titanium (Ti) directly on the substrate (tape base film) by vapor deposition or sputtering before forming the magnetic layer.
By depositing, it is possible to give the intermediate layer a curvature opposite to that of the deposited metal (alloy), thereby improving the cutability and improving the stiffness of the base tape film.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Example As shown in Figure 4, a base film (tape) of polyethylene terephthalate with a thickness of 15 μm 1
was prepared, and an aluminum intermediate layer 2 with a thickness of 25 nm was formed thereon by vacuum evaporation. next,
A ferromagnetic layer (Co-Ni layer) A is applied to the aluminum intermediate layer 2 of the tape, which runs in contact with the cooling can (drum), by using a ferromagnetic material cobalt-nickel (Co-Ni) by oblique evaporation. ₁ was formed. In this oblique deposition method, the minimum (or maximum) of the deposition flow is
By adding oxygen (O ₂ ) gas near the incident angle,
Near the end of the Co--Ni layer deposition, a Co--Ni oxide was deposited to form an oxide layer _B1 . For vapor deposition, the pressure is set to 3 x 10 ^-3 Pa (approximately 2 x 10 ^-5 Torr), Co-Ni is heated and melted with an electron beam (EB) to generate a vapor deposition flow, and the cooling can is maintained at 0°C. did. The coercive force of the resulting Co-Ni layer _A1 in the tape length direction is approximately
It was set to be 6000e or higher. This process of vapor deposition of the Co-Ni layer and the oxide layer was repeated (twice,
The magnetic layer 3 was formed by repeating the process 3 times, 4 times, and 5 times. Note that FIG. 4 shows a three-layer structure that is repeated three times. The thickness of magnetic layer 3 is 200nm.
The thicknesses of the Co--Ni layer and the oxide layer were determined according to the multilayer structure so as to be constant. For example, in the case of a three-layer structure (Fig. 4), the Co-Ni layer A ₁ is 50 nm thick, A ₂ and A ₃ are 60 nm thick, and the oxide layers B ₁ , B ₂ ,
_B3 was set to 10 nm. In addition, if it has a four-layer structure, Co
−Ni layers A ₁ to _{A 4} are 40 nm thick, and oxide layers B ₁ to _{B 4} are
It was set to 10 nm.

Under the above conditions, a deposited film of a nonmagnetic intermediate layer and a multilayered magnetic layer was formed. At this time, the relationship between the number of ferromagnetic layers in the magnetic layer and the sensitivity was as shown in FIG.
In the figure, the sensitivity is shown in the form of a cassette tape cut to a width of 3.8 mm, and a relative output of 333 Hz at 4.75 cm/sec. According to this, when the number of layers is 1 or 2, this tape does not show very good sensitivity, but
On the other hand, it has become clear that tapes consisting of three or more ferromagnetic layers exhibit superior sensitivity.

Next, when making the sample shown in FIG. 4, samples with different degrees of oxidation were obtained by changing the oxygen partial pressure to several pressures during the deposition of the cobalt-nickel oxide layer including the top layer. However, at this time, the incident angle during oblique deposition was adjusted so that the coercive force of the ferromagnetic layer (Co--Ni layer) was approximately 6000e or more. The oxygen partial pressure and electrical resistance of the tape surface at the time of forming the uppermost layer of the sample obtained as described above were as shown in FIG. Here, electrical resistance refers to the electrical resistance measured at both ends of a tape with a width of 3.8 mm and a length of 20 cm. In addition, when examining the relationship between the degree of oxidation and noise for the obtained sample, as mentioned above, the surface electrical resistance is low;
The conductive tape is a 3-head type deck, and if the head is poorly sealed, the noise contained in the playback signal will be greater when recording and playing back at the same time than when simply playing back. This relaxation is achieved by forming an upper layer. That is, if the difference between the two noise levels is shown in relation to the electrical resistance of the tape surface, the result will be as shown in FIG.

Here, the noise level is a 333Hz noise component.

According to FIG. 3 above, tapes with a surface electrical resistance exceeding 200Ω have a noise level difference of 1 dB or less, which poses no problem in practical use. At this time, the sensitivity is several 10
Since it was only about 1 dB lower than the Ω sample, the SN ratio of the tape was improved by the amount that the noise level difference disappeared, and it was within a range that did not cause any practical problems.

Note that this tendency of noise level difference was the same everywhere in the audio frequency domain. Also, even if there are four or more ferromagnetic layers, if the resistance is 200Ω or more, the noise level difference will be the same as in the embodiment of this invention.
It will be less than 2dB.

As explained in detail above, the magnetic recording medium according to the present invention solves the problem of noise that is inevitable when putting vapor-deposited tape into practical use, and has a remarkable industrial effect. Furthermore, when an intermediate layer such as aluminum is deposited, the aluminum deposited layer warps together with the base (tape) due to the internal stress generated in the aluminum deposited layer, but the ferromagnetic layer internal stress that occurs when the ferromagnetic (Co-Ni) layer is deposited. Since the stress in the opposite direction causes the warp to occur in the opposite direction, the results cancel each other out, and the occurrence of warp in the vapor-deposited tape (magnetic recording medium) can be made much smaller than in the past. Furthermore, the formation of the intermediate layer improves the stiffness of the tape (substrate) (that is, makes it stiffer) and improves the contact with the magnetic head.

In addition, in the formation of the intermediate layer, ferromagnetic layer, and oxide layer shown in the examples, it is possible to change the method without departing from the gist of the present invention, and ion plating, sputtering, etc. may also be used. It is something. In particular, the relationship between the oxygen atmosphere and the electrical resistance is influenced by other conditions, such as the evaporation rate and the movement rate of the substrate, so this does not limit the effective scope of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged sectional view of a magnetic recording medium (vapor-deposited magnetic tape) according to the present invention, and FIG. 2 is a relationship between the number of ferromagnetic layers and sensitivity of the magnetic tape obtained in an example of the present invention. , Figure 3 shows the relationship between the oxidation partial pressure in the vacuum chamber and the electrical resistance of the finished tape surface when forming the oxide layer in a three-layer magnetic layer, and Figure 4 shows the relationship between the oxidation partial pressure in the vacuum chamber and the electrical resistance of the finished tape surface. FIG. 3 is a diagram showing the relationship between surface electrical resistance and noise level difference in the case of a three-layer magnetic layer consisting of an oxide layer.

Claims (1)

[Claims] 1. A non-magnetic substrate 1; a non-magnetic intermediate layer 2 formed on the non-magnetic substrate 1; and three or more ferromagnetic layers A ₁ formed on the non-magnetic intermediate layer 2. , ~A ₃ and oxide layers B ₁ and ~B ₃ formed by oxidizing the ferromagnetic material constituting each ferromagnetic layer. 2 The magnetic recording medium has a width of 3.8 mm and a length of
2. The magnetic recording medium according to claim 1, wherein the electrical resistance measured at both ends of 20 cm is 200Ω or more.