JPS6113366B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a heat-treated magnetic thin film with excellent corrosion resistance. The magnetic thin film has a multilayer thin film structure composed of cobalt as a magnetic material and at least one non-magnetic layer, and is produced by a method such as a vacuum evaporation method, an ion plating method, or a sputtering method. It is formed on a substrate of polymer, glass, ceramics, metal, etc. Cobalt, like iron, a transition metal, is a metal that corrodes easily. Therefore, cobalt thin films obtained by conventional methods, such as simple vapor deposition, are susceptible to rust and cannot be practically used as magnetic tapes. The present invention improves and improves the corrosion resistance especially when cobalt is used as the magnetic material. In general, for magnetic thin films, it is better to form a multilayer film in which a non-magnetic layer is sandwiched between a substrate and a magnetic layer, or between magnetic layers, than to form a single thick magnetic layer. Conversion characteristics etc. are improved. In particular, when the nonmagnetic layer is a metal with a low standard free energy of oxide formation, the electromagnetic conversion characteristics are particularly improved. On the other hand, from the perspective of corrosion, when a magnetic cobalt layer and a non-magnetic layer are combined, and the non-magnetic layer is made of a conductive material such as a metal that has an effect on electromagnetic properties as described above, By superimposing or contacting cobalt, a contact electromotive force is generated, which is undesirable from a corrosion resistance point of view due to a kind of battery action. Usually, when a thin film of cobalt metal is formed on a substrate such as a polymer film by a method such as vacuum evaporation, a cobalt thin film made of pure cobalt is formed. This cobalt thin film was immersed in an aqueous solution at 30°C (hereinafter referred to as electrolyte solution) containing 0.02M/borax and 0.1M/borax.
After minutes, the natural electrode potential of nearly pure cobalt is −
Indicates a potential around 0.50V to -0.55V (hereinafter written as vs. SCE for a saturated electrode). Alternatively, silver is first vapor-deposited on a polymer film, etc., and then cobalt is vapor-deposited as described above.
Even in the case of a multilayer structure, when immersed in an electrolyte solution, it settles to the natural electrode potential of almost pure cobalt after 1 to 2 minutes, as in the case of a vapor-deposited layer of only cobalt. When this multilayer structure thin film is heat-treated at, for example, 100°C, its surface is mainly oxidized, and when it is immersed in an electrolyte solution, it exhibits a potential more positive than -0.50V at the moment of immersion, but after 3 minutes of immersion. Although the potential shown may differ depending on the combination of cobalt and different metals, it only shows a value of -0.20V or less. Here, the electrolyte solution is an aqueous solution containing 0.02 mol of borax and 0.1 mol of boric acid in 1 part distilled water, and is bubbled with nitrogen gas for about 10 minutes to remove the oxygen dissolved in the aqueous solution. This is a solution substituted with The electrolyte solution shall be left standing without stirring while the magnetic thin film is immersed. When measuring the potential of a thin film, a gold wire is used as a lead wire, and it is fixed in contact with the thin film using conductive paint.
The measurement was carried out by fixing the gold wire with a resin that hardens at room temperature. When the substrate was a polymer film or the like, the sample was fixed at several points on the glass preparation with a room-temperature curing resin to prevent the sample from moving. On the other hand, when the magnetic thin film produced by the manufacturing method of the present invention is immersed in an electrolyte solution, the natural electrode potential of the heat-treated magnetic thin film after 3 minutes of immersion is more positive than -0.20 V with respect to the saturated electrode. This shows the potential of As described above, it is known that cobalt having a potential more positive than -0.20 V can be obtained by anodizing a cobalt metal such as a cobalt plate in an electrolyte solution. However, the cobalt thin film produced in an oxygen atmosphere under reduced pressure as in the present invention has a thickness of several hundred to several hundred nanometers.
Since the thickness is several thousand Å, if electrolytic treatment is performed, it will dissolve in the electrolyte solution, making it difficult to maintain the thin film shape. Therefore, the magnetic thin film of the present invention does not improve the corrosion resistance of cobalt thin films by known methods such as anodic oxidation. The magnetic thin film produced by the manufacturing method of the present invention is a thin film that exhibits a high potential without being anodized, similar to the one that is anodized, and has improved corrosion resistance due to the effect of heat treatment. It is. Although anodizing is performed in a solution, the thin film of the present invention is not formed in a solution.
It is thought that the structure of a thin film exhibiting a high potential is different from that formed in a solution in many respects. The effects of heat treatment are as follows. When cobalt and a non-magnetic layer are combined, or when a metal that is effective in electrode conversion properties is used for the non-magnetic layer, corrosion resistance is worse than a thin film made of only cobalt, especially in the untreated state after forming a multilayer thin film. There is a strong tendency to On the other hand, it has been found that when this multilayer thin film is heat-treated, its corrosion resistance is significantly improved to the same level as that of heat-treated cobalt, or even better. However, heat treatment does not improve corrosion resistance in all cases. In other words, when the magnetic thin film after heat treatment is immersed in an electrolyte solution, the magnetic thin film whose natural electrode potential after 3 minutes of immersion is more positive than -0.20V with respect to the saturated electrode is particularly corrosion resistant. It was excellent in As described above, when the thin film produced by the manufacturing method of the present invention combines cobalt with a nonmagnetic layer, especially a metal, etc., the corrosion resistance was inferior to that of a thin film made of cobalt alone before heat treatment, but after heat treatment, the natural electrode potential ( A thin film whose 3-minute post-immersion value (vs. SCE) shows a potential more positive than -0.20 V has corrosion resistance comparable to or even better than that of cobalt. In addition, there was no tendency for the magnetic properties to deteriorate due to heat treatment, and on the contrary, they began to exhibit stable properties that did not change over time. Note that the nonmagnetic layer described in the present invention is a substance that does not exhibit ferromagnetism. The multilayer thin film structure composed of cobalt and at least one nonmagnetic layer may be any structure having at least one structure in which cobalt and a nonmagnetic layer are in contact with each other on the substrate. For example, the cobalt layer is C and the nonmagnetic layer is
As an example of a multilayer thin film structure in the case of A ₁ , A ₂ , A ₃ , A ₄ ..., A ₁ /C, A ₁ /A ₂ /C, A ₁ /C/
A ₁ /C, A ₁ /C/A ₂ /C, A ₁ /A ₂ /C/C,
A ₁ /C/A ₂ /C/A ₃ /C, etc. In this case, the outermost layer may be coated with a metal other than cobalt or with a suitable material. However, in this case, the natural electrode potential of the cobalt surface cannot be measured. In such cases, the outermost layer should be heat treated before being coated with a material other than cobalt to achieve a natural electrode potential more positive than -0.20V (3 minutes after immersion, vs. SCE).
When this is indicated, such magnetic thin films are also included in the present invention. As an example, Figure 1 shows the time dependence of the natural electrode potential measured in an electrolyte solution after heat-treating a thin film made of aluminum as the first layer and cobalt as the second layer on a polyethylene terephthalate film at 110°C. Indicated. The thin film of the present invention exhibiting a natural electrode potential (value 3 minutes after immersion, versus SCE) more positive than -0.2 V after heat treatment was obtained in the following manner. FIG. 2 briefly shows a method (apparatus) for forming a magnetic thin film. For example, titanium was evaporated onto the polyester film as a nonmagnetic layer. Next, cobalt was heated and evaporated with an electron beam by running the polyester film continuously under the introduction of oxygen at an incident angle of 10° or more to obtain a continuous vapor-deposited film of cobalt. This magnetic thin film was continuously heated along a heated roller at 125°C. In FIG. 2, 1 is the substrate film that is wound from the unwinding roll 2 around the can 3 to the take-up reel 4, 5 is the cobalt evaporation source, 6 is the mask, and θ is the incident angle in the case of oblique evaporation. It is. The thin film formation conditions under reduced pressure are determined by many factors, such as the substrate temperature during thin film formation, the degree of vacuum (the relationship between the pumping speed and the amount of gas introduced), the amount of oxygen introduced, the rate of crystal formation, and the amount of evaporated material on the substrate. In particular, in order to obtain a magnetic film with excellent corrosion resistance as in the present invention, the amount of oxygen introduced and the evaporated material are Since it is highly dependent on the incident angle to the substrate and the evaporation rate, it is clear that it is deeply related to the reaction system between cobalt and oxygen and the crystal formation system. Before heat treatment, cobalt thin films tend to have worse corrosion resistance than cobalt alone, depending on the combination with the nonmagnetic layer, but after heat treatment, the corrosion resistance becomes equal or even better, although it is not clear why. Since the higher the rate of improvement in the natural electrode potential, the more difficult it is to rust, it is thought that the bond with oxygen formed during vapor deposition is further stabilized by heat treatment. The heat treatment conditions for a cobalt magnetic thin film, which has a multilayer thin film structure with a non-magnetic layer, depend on the manufacturing conditions of the cobalt magnetic thin film, but for example, in the case of a polyester film substrate, corrosion resistance is significantly improved when treated at approximately 90 to 120°C. Get better. Since the heat treatment temperature is more effective at 90°C or higher, the heat treatment should be performed at 90°C or higher. A magnetic thin film made of cobalt and various non-magnetic layers.
Table 1 below shows the results of a corrosion resistance test conducted in a humid atmosphere of 60°C and 90% RH. A magnetic thin film exhibiting a natural electrode potential (value for 3 minutes after immersion, vs. SCE) more positive than -0.20V was particularly excellent in corrosion resistance.

[Table] Specific examples are shown below. Example 1 A polyester tape with a thickness of 10 μm and a length of 500 m was deposited at a can temperature of 70°C and an incident angle of 20° (first
Chromium was deposited over a length of 100 m by electron beam heating with an oxygen gas flow rate of 0.2/min and an accelerating voltage of 10 KV. Next, a cobalt thin film was formed on this chromium at an incident angle of 30° and an oxygen gas flow rate of 0.2/min. This thin film will be referred to as A hereinafter. Next, chromium was formed as a first layer on the polyester tape in the same manner as above, and cobalt was vapor-deposited on the chromium without introducing the mask 6 of FIG. 2 and introducing oxygen. This thin film will be referred to as B hereinafter. Half of each of the above two thin films A and B is 110
The film was heat-treated at a film running speed of 20 m/min using a hot roll kept at a constant temperature. These heat-treated thin films are referred to as A' and B', respectively. Below, the evaluation of the thin films produced in each example is shown in Table 2.
They are summarized in . Example 2 Titanium was continuously deposited on the same polyester film as in Example 1 without using a mask and without introducing oxygen. Cobalt was deposited on this titanium without using a mask and without introducing oxygen, as in the case of titanium deposition. This thin film will be referred to as C hereinafter. Next, cobalt was deposited obliquely on the titanium formed as the first layer using a mask at an incident angle of 30°.
A cobalt thin film was formed under the condition that the amount of oxygen gas introduced was 0.15/min. This thin film will be referred to as D hereinafter. As in Example 1, each half of thin films C and D was heat treated using a hot roll at 115°C. This heat-treated thin film is shown below.
They are called C′ and D′. Example 3 On the same polyester film as in Example 1, the can temperature is 70°C, the incident angle of oblique evaporation is 30°, and the amount of oxygen gas introduced.
Aluminum was formed as a first layer using an electron beam at 0.24/min. Under these conditions, cobalt was then formed as a second layer, and this same operation was repeated twice to form thin films of aluminum, cobalt, aluminum, and cobalt in this order on the polyester film. Hereinafter, this thin film will be referred to as E, and as in Example 1,
The thin film heat-treated at 120° is called E′. Example 4 Aluminum was continuously evaporated onto the same polyester film as in Example 1 without using a mask at an amount of oxygen gas introduced at 0.5/min.
Cobalt was deposited using an electron beam at 0.5/min and an acceleration voltage of 30 KV. Hereinafter, this thin film will be referred to as F, and the thin film heat-treated in the same manner as in Example 3 will be referred to as F'. As described above, each thin film of Examples 1 to 4 was formed by attaching a gold lead wire with a conductive paint, and then immersed in the electrolyte solution of the present invention, and the natural electrode potential after 3 minutes of immersion. (vs. SCE) was measured. In addition, each thin film was left in a humid atmosphere at 60° C. and 90% RH for 5 hours to test its corrosion resistance. It is shown in the table below.

[Table] As shown above, many combinations of cobalt and nonmagnetic layers have particularly poor corrosion resistance before heat treatment.
Those that were heat-treated and showed a natural electrode potential (3-minute value, vs. SCE) more positive than -0.2V after heat treatment had excellent corrosion resistance. Due to this excellent corrosion resistance, it can be used as a magnetic thin film without impairing the magnetic properties that can be improved by combining with a nonmagnetic layer. In particular, it has great benefits for practical applications such as magnetic tape. In addition, above, we described the combination of cobalt and nonmagnetic layer by electron beam heating.
It is not limited to a thin film formation method simply by vapor deposition, but is a thin film formed under a pressure lower than 1 atm, and when immersed in an electrolyte solution at 30°C after heat treatment, 3 minutes after immersion. Natural electrode potential (vs.
Any magnetic thin film exhibiting a potential SCE) more positive than -0.20V is sufficient. As described above, according to the present invention, a magnetic thin film with excellent corrosion resistance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the time dependence of the natural electrode potential of a magnetic thin film in an electrolyte solution, and FIG. 2 is a schematic diagram of the main parts of a manufacturing apparatus in the method for manufacturing a corrosion-resistant magnetic thin film of the present invention. 1...Substrate film, 5...Cobalt evaporation source.

Claims (1)

[Claims] 1. After forming a thin film by layering cobalt and a non-magnetic metal layer on a substrate film in an oxygen atmosphere under reduced pressure, this thin film is heat-treated to form a magnetic thin film, and this magnetic thin film is coated with borax 0.02M/ and boric acid
The magnetic thin film is immersed in an aqueous solution at 30°C containing 0.1M/3 minutes after the immersion, the natural electrode potential of the magnetic thin film is more positive than -0.20V with respect to the saturated electrode. A method for manufacturing a corrosion-resistant magnetic thin film as selected.