PROCESS FOR PREPARING MAGNETIC LAYER AND MAGNETIC HEAD PREPARED USING THE SAME

Abstract: Ion implantation is conducted in a desired area(s) of the surface of a magnetic layer, and annealing of the layer is carried out to control the composition in that desired area(s). The control of the composition may be facilitated by applying a one-directional or rotating magnetic field during ion implantation. In preparing a magnetic head, a portion of a magnetic pole at least on one side thereof in close proximity to a magnetic recording medium is formed into an iron or iron-based magnetic alloy film, at least part of which is subjected to ion implantation and annealing.

Description: The present invention relates to a process for preparing a magnetic layer, particularly a process for preparing a magnetic layer suitable for magnetic recording. Further, the present invention relates to a magnetic head, particularly a magnetic head using as part of a magnetic pole a magnetic material having an extremely high saturation induction Bs (Bs = 4πMs, wherein Ms is saturation magnetization) which is prepared according to the above-mentioned process. A magnetic layer having a high saturation induction and a high permeability is suitable for improving recording characteristics in a magnetic recording device. For the purpose of obtaining this kind of magnetic layer, a layer (film) of a magnetic compound has been formed by a low vacuum deposition method, a gas atmosphere deposition method, a sputtering method, or the like as described in "Appl. Physics Lett." Vol. 20, No. 12, P. 15 (1972), T.K. Kim and M. Takahashi: "New Magnetic Material Having Ultrahigh Magnetic Moment" or "Solid State Physics" Vol. 7, No. 9 (1972) p.3(483), Science Press Inc., Tokyo Japan, M. Takahashi: "Magnetism for Fe Films Evaporated in Nitrogen". However, these known thin film deposition technologies have a defect that they are so poor in reproducibility that they provide large batch-to-batch variation of recording characteristics between magnetic layers formed because of not only large scattering or variation of magnetic characteristics thereof but also a difficulty encountered in controlling ambient conditions, etc. during magnetic layer formation. Furthermore, since a magnetic compound is formed on a substrate in vacuo or in a gas atmosphere at once, no consideration has been given at all to the control of the composition and magnetic characteristics of the magnetic layer surface only in the desired areas. Furthermore, according to PATENT ABSTRACTS OF JAPAN, Vol.8, n.33 (P-254) [1470], Feb. 14, 1984, unexamined applications, P section, JP-A-58-188318, ion implantation into the surface of a head having an Fe-Si-Aℓ alloy core was described. The wear resistance of the head should be improved, in particular by O and N forming oxide and nitride respectively. The magnetic head will now be discussed as an instance of magnetic recording devices. Magnetic recording has been making remarkable progress in recent years by virtue of development of magnetic tapes with high coercive force and high performance head materials for the above-mentioned tapes. Especially when a metal tape having a high coercive force is used, a remarkable increase in output and an increase in O/N (output to noise) ratio are attained in a high recording density area ranging from several pm to 1 µm in recording wave length. Thus a marked improvement in recording density is being attained in the fields of VTR, etc. where a high recording density is required. However, a magnetic head using ferrite which has heretofore been used in VTR, etc. does not have a sufficient recording magnetic field because the saturation induction of ferrite is about 0.5T (5000 G) or lower. Thus a magnetic head using a metal magnetic material having a high saturation induction has been demanded for use with a metal tape with a high coercive force. Examples of such a metal magnetic material include an Fe-Aℓ-Si alloy (saturation induction: about 1 T), an Fe-Ni alloy (saturation induction: about 0.8 T), an Fe-Si alloy (saturation induction: about 1.8 T), systems of at least one of Fe, Co, and Ni containing B, C, N, Aℓ, Si, P, etc. incorporated thereinto, and metal-metal amorphous alloy systems of at least one of Fe, Co, and Ni containing Y, Ti, Zr, Hf, Nb, Ta, etc. incorporated thereinto, of which an Fe-Si alloy having a Si content of about 6 wt. % is a material having the highest saturation induction of about 1.8 T. On the other hand, the gap length of the VTR magnetic head has become smaller and smaller in recent years for realizing high density magnetic recording. The conventional gap length of 0.5 µm has recently been reduced to 0.3 µm, which must be further reduced to 0.1 to 0.2 µm in future. When the gap length is reduced as described above, the strength of a stray field from the head is markedly decreased. Further, the coercive force of the magnetic recording medium is being increased steadily for realizing high density magnetic recording. The coercive force, about 2.4 x 10⁴ A/M (300 Oe) of the conventional oxide type magnetic tape has been increased to about 5.6 x 10⁴ A/M (700 Oe). Even a tape having a coercive force of about 11.9 x 10⁴ A/M (1,500 Oe) is now produced as a result of recent development of a magnetic tape using a metal magnetic powder. When a magnetic head having a small gap length as mentioned above is used with a magnetic tape having such a very high coercive force, there arises a problem of insufficiency of the recording capacity in a long wavelength area. Thus a magnetic head material having as high a saturation induction as possible is needed. In future, the coercive force of the magnetic recording medium will be further increased while the gap length of the magnetic head will be further reduced. In view of such a trend, a high saturation induction will be more and more required of the magnetic head material. As regards the magnetic head for perpendicular magnetic recording which has recently been increasingly studied, the thickness of the main pole with which recording and playback are made on the perpendicular magnetic recording material must be extremely reduced for improving the recording density. Where the main pole is extremely thin, magnetic saturation is liable to occur at the tip of the magnetic pole in recording. When magnetic saturation occurs, there arises a problem of a difficulty in recording on the perpendicular magnetic recording medium. To solve such a problem, the saturation induction of the magnetic material used in the main pole must be increased as much as possible. The same problem is involved in the conventional thin film head for longitudinal magnetic recording which is employed in computer memories and the like. More specifically, since the thin film head has a small crosssectional area of the magnetic pole in close proximity to the functional gap, magnetic saturation is apt to occur. Accordingly, also in the thin film head, a magnetic head material having a high saturation induction is much demanded. An object of the present invention is to provide a process for preparing a magnetic layer with high reproducibility and with high controllability by eliminating scattering or variation in the magnetic characteristics of the magnetic layer which will occur in the aforementioned thin film formation. More particularly, an object of the present invention is to provide a novel process for preparing a magnetic layer which is adapted to an improvement in the recording characteristics by controlling the composition and magnetic characteristics of the magnetic layer surface only in the desired areas. Another object of the present invention is to provide a magnetic head having a superior recording characteristics to those of the conventional one by forming a magnetic pole thereof from a magnetic material having a higher saturation induction than that of the conventional one. In the conventional methods including the gas atmosphere deposition method, it is impossible to control the number of atoms in the magnetic layer formed. Accordingly, the magnetic characteristics of the magnetic layer formed show large variation (place-to-place in the same layer, and/or lot-to-lot) depending on a minute difference in an environment (degree of vacuumness, etc.). The first feature of the present invention consists in controlling the composition and characteristics of the magnetic layer with presicion and with high reproducibility by injecting a desired number of ions into the magnetic layer by ion implantation and thermally diffusing the ions by heat treatment to attain uniformity. The second feature of the present invention consists in obtaining a magnetic head having superior recording characteristics to those of the conventional one by constituting that portion of a magnetic pole thereof at least on one side thereof which is adjacent to the magnetic recording medium with an thin iron or iron-based magnetic alloy film, in at least part of which an area containing at least one element selected from among nitrogen carbon and boron is formed by ion implantation and annealing to provide a higher saturation induction in the above-mentioned element-containing area than that of the conventional high saturation induction magnetic material. It is known that, when thin iron film formation is made in an atmosphere containing nitrogen by vacuum deposition or sputtering, a film having a higher saturation induction than that of iron can be obtained if the conditions are adequate (see the aforementioned "Solid State Physics" Vol. 7, No. 9 (1972) pp. 483-495). However, in the preparation of a film having a high saturation induction according to this method, a troublesome operation of accurately controlling partial pressure of nitrogen in the atmosphere and the temperature of a sample is needed. If the conditions are outside the adequate ranges, the saturation induction is drastically reduced, thus presenting a problem. According to the present invention, the above-mentioned problem is solved by injecting or incorporating nitrogen into an iron or iron-based magnetic alloy film by ion implantation. The ion implantation method has a merit that the nitrogen density of the above-mentioned film per unit area thereof can be easily controlled. Accordingly, a magnetic layer having a high saturation induction can be easily prepared. The same outcome can be obtained where carbon or boron is used instead of nitrogen. Additionally, Phys. Status Solids, Vol. 80, No. 1, pp. 211-222 (1983) mentions an instance of injection of nitrogen into iron or an iron-based alloy by ion implantation. However, it makes no mention of any magnetic characteristics of a sample obtained. Stated in more detail, in the magnetic head for perpendicular magnetic recording according to the present invention, at least one element selected from among nitrogen, carbon, and boron is injected or incorporated into a portion of the main pole adjacent to the surface facing a magnetic recording medium by ion implantation after formation of the main pole with a thin film of iron or an iron-based magnetic alloy to increase the saturation induction of the iron or the iron-based alloy in the portion subjected to the ion implantation. Thus a perpendicular magnetic recording magnetic head having excellent recording characteristics can be obtained. In the magnetic head for longitudinal magnetic recording according to the present invention, at least a portion of the magnetic head adjacent to the functional gap-forming face is constituted by an iron or iron-based magnetic alloy film, and at least one element selected from among nitrogen, carbon, and boron is injected or incorporated into the iron or iron-based magnetic alloy film constituting the functional gap-forming face of the magnetic head by ion implantation to increase the saturation induction of the iron or iron-based magnetic alloy in the portion subjected to ion implantation. Thus a longitudinal magnetic recording head having excellent recording characteristics can be obtained. Another merit of the magnetic head for longitudinal magnetic recording according to the present invention is as follows. When a magnetic layer having a high saturation induction is deposited on the functional gap-forming surface of the magnetic head by vacuum deposition or sputtering, the interface between a magnetic substrate and the high saturation induction magnetic layer formed thereon is parallel with the gap face, whereby the contour effect appears. By contrast, when a magnetic layer having a high saturation induction is formed on the functional gap-forming face by ion implantation as in the present invention, the density of the implanted element is gradually varied in the direction of depth, and hence the saturation induction also is gradually varied in the same direction. Thus the contour effect advantageously tends hardly to appear. The same applies to a ring type head for perpendicular magnetic recording. As described above, in accordance with the present invention, there is provided a magnetic head having excellent recording characteristics. As to the magnetic head of the present invention, in some cases a magnetic layer having a high saturation induction ray be easy to obtain stably when the product subjected to ion implantation is heated at a temperature of 70 to 500 o C. When the heating temperature is higher than 500 o C, a phase having a high saturation induction may unfavorably be decomposed to decrease the saturation induction. In general, a magnetic alloy containing an interstitial element such as nitrogen, carbon, or boron in addition to iron or an iron-based magnetic alloy is known to have a magnetic anisotropy induced by magnetic annealing. This is because the interstitial element atoms contained in the iron or the iron-based magnetic alloy moves toward positions where they reduce the energy in the direction of magnetization to stabilize the direction of magnetization. When such an induced magnetic anisotropy is large, the permeability is low. Thus, in some cases the induced magnetic anisotropy is not desirable for the magnetic head. However, in some cases provision of an adequate degree of induced magnetic anisotropy in a given direction may be useful for the characteristics of the magnetic head. As described above, control of the degree and direction of the induced magnetic anisotropy is necessary for obtaining a magnetic head having excellent characteristics. The above-mentioned control of the induced magnetic anisotropy can be achieved by application of a magnetic field to a sample with heating. Additionally, in the present invention, the induced magnetic anisotropy can be controlled by applying a one-directional magnetic field or a rotating magnetic field to the inside of a sample during the course of ion implantation. The thickness of the ion-implanted layer formed by ion implantation according to the present invention varies depending on the ion acceleration voltage. It is difficult for the ion-implanted layer to have a thickness above about 1 µm. Therefore, the following procedure may be taken for obtaining an ion-implanted layer having a thickness of more than about 1 µm. Specifically, a plurality of repetitions is made of the steps of forming a thin film of iron or an iron-based magnetic alloy having a thickness of 1 µm or less and implanting ions into the film to form an ion-implanted layer. In this way, lamination of ion-implanted layers is made to obtain an ion-implanted layer having a thickness of more than about 1 µm. Further, improvements in magnetic characteristics such as coercive force and permeability may be made by interposing a ferromagnetic or non-magnetic intermediate layer(s) between respective ion-implanted layers as mentioned above or blocks each of a plurality of ion-implanted layers. Fig. 1 is a diagram showing a relationship between the saturation magnetization Ms of the Fe film subjected to N⁺ ion implantation and the amount of N⁺ ion dose in one embodiment of this invention. Figs. 2 and 3 are an Fe-N phase diagram and a diagram showing a relationship between the saturation magnetization Ms of the Fe-N compound and the amount of N, respectively. Fig. 4 is a diagram for illustrating changes in saturation magnetization Ms depending on the amount of N⁺ ion dose in the Fe film and the formation of N compounds. Fig. 5 is a diagram showing the saturation magnetization Ms of the Fe-N film prepared by a known environment control technique. Figs. 6(a) and (b) are diagrams each showing a depth of ion implantation and an ion distribution in ion implantation. Figs. 7(a) and (b) are views illustrating preparation of a multi-layer magnetic layer by ion implantation. Fig. 8 is a view showing a laminate structure composed of magnetic layers and non-magnetic layers and prepared by ion implantation. Figs. 9(a) and (b) are diagrams showing a magnetic layer prepared by ion implantation through a mask in another embodiment of the present invention. Fig. 10 is a diagram showing changes in the average N density in the Fe film and the ratio of increase of saturation induction against the amount of N⁺ ion implantation into the Fe film. Figs. 11(a) and (b) are rough illustrations of the process for preparing a perpendicular magnetic recording head as an embodiment of this invention. Fig. 12 is a plan view of the magnetic head as shown in Figs. 11(a) and (b). Figs. 13(a) to (g) are rough illustrations of the process for preparing a longitudinal magnetic recording head as another embodiment of this invention. An embodiment of this invention will now be described with reference to Fig. 1. Fig. 1 shows a relationship between the saturation magnetization Ms and the amount of N⁺ ion dose (O marks in the figure) and the dependency thereof on the annealing temperature (▵ and □ marks in the figure) in the case where N⁺ ions are implanted, at an acceleration voltage of 160 KeV, into an about 300 nm thick Fe film prepared by known vacuum deposition or sputtering method, or other known methods. In the case of only ion implantation into the Fe film, the saturation magnetization of the ion-implanted layer is substantially the same as the value of the Fe bulk (∼ 0.1720 T) up to a critical dose (1 x 10¹⁶ cm⁻²) and then rapidly decreases to about 0.05 T at a dose of 2 x 10¹⁷ cm⁻². On the other hand, when the N⁺ ion-implanted Fe film is subjected to heat treatment or annealing, for example, at 300 o C or 450 o C, the saturation magnetization Ms temporarily increases to a far larger value than that of pure Fe (about 0.22 T at a dose of 5 x 10¹⁶ cm⁻²) and then decreases. Figs. 2 and 3 are an Fe-N phase diagram and a diagram showing a relationship between the saturation magnetization and the amount of N in nitrogen compounds of Fe (in a region of low N concentration). As shown in Fig. 3, in the nitrogen compounds of Fe, the saturation magnetization increases with a decreasing N concentration. It is known that the saturation magnetization of Fe₈N is far higher (about 0.22 T) than the value of pure Fe. Fig. 4 shows the dependency of nitrogen compounds of Fe present in the N⁺ ion-implanted Fe films, analyzed according to an X-ray diffraction measurement, on the amount of ion dose for explaining Fig. 1 concerning an embodiment of this invention. The saturation magnetization Ms of the N⁺ ion-implanted Fe film decreases with formation of Fe₄N, Fe₃N, and Fe₂N as the N⁺ ion dose increases in a range of 10¹⁶ to 10¹⁸ cm⁻². On the other hand, in the N⁺ ion-implanted Fe films subjected to heat treatment or annealing, with an increasing N⁺ ion dose, Fe₈N with a larger saturation magnetization than that of pure Fe appears at a N⁺ ion dose of about 5 x 10¹⁶ cm⁻² and, subsequently, Fe₄N, Fe₃N, and Fe₂N appear with a decrease in the saturation magnetization Ms. Thus a film having a desired saturation induction Ms can be prepared with a nitrogen compound of Fe by specifying the N⁺ ion dose and the annealing temperature. For example, when Fe₈N with a saturation magnetization Ms of 0.22 T is to be formed, a suitable N⁺ ion dose is 10¹⁶ to 10¹⁷ cm⁻² and a suitable annealing temperature is 300 to 500 o C. When Fe₃N with a saturation magnetization Ms of about 0.1 T is to be formed, a suitable N⁺ ion dose is 10¹⁷ to 10¹⁸ cm⁻² and a suitable annealing temperature is about 300 to 400 o C. Fig. 5 shows a relationship between the saturation magnetization Ms of the Fe film prepared in an atmosphere of N₂ by a well-known sputtering method and the gas pressure. As shown by the dotted line in Fig. 5, the saturation magnetization Ms of the Fe film temporarily increases over the value for pure Fe by virtue of the presence of N even if the degree of vacuum is decreased. In the films prepared in an atmosphere of N₂ as shown by the solid line, scattering of the saturation magnetization of the film is extremely large. Besides, it is known that the magnetic characteristics of the film prepared by this sort of method is extremely poor in reproducibility. Figs. 6(a) and (b) illustrate an embodiment of the present invention wherein a layer of a magnetic compound having a single composition is formed by multiple ion implantation. Fig. 6(a) shows an ion distribution, in the direction of depth, of a layer formed by single ion implantation. As is known, this distribution constitutes a Gaussian distribution showing a concentration gradient. In this case, the composition distribution of the magnetic compound appears in the direction of thickness of the magnetic layer. On the other hand, according to the multiple ion implantation method as an embodiment of this invention, a layer of a magnetic compound having a single composition is formed when the acceleration voltage is so changed as to add Gaussian distributions (I + II + III). As a result, the magnetic characteristics of the compound layer (saturation magnetization, magnetic anisotropy, etc.) is rendered uniform in the direction of layer thickness. Figs. 7(a) and (b) illustrate another embodiment of this invention. A magnetic layer 3 is formed through a step of magnetic layer deposition 1, a step of ion implantation 2, and a step of annealing as shown in Fig. 7(a). A thick layer of an ion-implanted magnetic compound having a multiple-layer structure 3a, 3b, 3c, and 3d is formed by repeating the above-mentioned steps as shown in Fig. 7(b). According to the current ion implantation technique, the depth of ion implantation is limited to at most several MeV due to the limitation of an accelerator. According to the multiple structure materialized in the present invention, however, a thick layer of a magnetic compound having a single composition and a desired thickness can be formed without being adversely affected by the limitation of the accelerator. Fig. 8 shows a magnetic layer structure formed by alternately laminating ion-implanted magnetic compound layers 4 and non-magnetic layers 5 according to still another embodiment of this invention. In the usual magnetic layer, the magnetic characteristics such as coercive force and permeability are largely influenced by the layer thickness. When the laminate structure including non-magnetic layers according to this embodiment of this invention is adopted, a desired multi-layer structure layer of a magnetic compound keeping the desired magnetic characteristics inherent to a thin layer of that compound, as they are, can be obtained. Fig. 9 shows a compound distribution of the surface of a magnetic layer in the case where ion implantation is made through a mask as an application embodiment of this invention. As shown in Fig. 9(a), a mask 8 is formed on the magnetic layer 7 prepared on a substrate 6. When ion implantation is made over the mask 8, a pattern consisting of ion-implanted magnetic layers 9 and magnetic layers 10 not subjected to ion implantation is formed as shown in Fig. 9(b). According to the present invention, a desired layer of a magnetic compound can be formed with high reproducibility by directly specifying the number of atoms and the annealing temperature unlike the processes requiring a very delicate control of parameters such as an atmospheric parameter involving a degree of vacuum or a gas pressure. Although Fe-N compounds were described hereinabove, not only binary magnetic compounds such as Ni-N system, Co-Zr system, Fe-Tb system, Gd-Co system, Fe-B system, and Fe-Si system but also ternary magnetic compounds such as Fe-Mn-Si system can provide a magnetic layer having the same effects as hereinbefore described by ion implantation of a second element and a third element. Moreover, the saturation magnetization Ms, the anisotropic magnetic field Hk, the permeability µ, and the like become controllable according to the present invention. As described above, according to the present invention, control of a composition in desired areas can be easily made, and hence a layer of a magnetic compound can be selectively formed, for example, into a mosaic pattern besides a stripe pattern as shown in Fig. 9(b). According to the present invention, a desired number of ions are injected into a magnetic layer by ion implantation as hereinbefore described, and thermally diffused by annealing to achieve uniformity for forming a desired layer of a magnetic compound. Thus, magnetic layers that may be utilized as magnetic bubble domain memory elements, magnetic heads, magnetic recording media, etc. can be formed with high reproducibility. The following Examples will illustrate preparation of magnetic heads according to the foregoing process for preparing a magnetic layer with reference to Figs. 10 to 13. Example 1 A thin iron film having a thickness of 0.15 µm was deposited on a glass substrate by sputtering. Subsequently, nitrogen ions are implanted into the above-mentioned thin iron film, and the substrate was annealed at 350 o C for 30 minutes. Changes in the average density of nitrogen and saturation induction of this iron film are shown in Fig. 10. As is apparent from Fig. 10, with an increase in the amount of N⁺ ion implantation, the average density of nitrogen in the iron film gradually increased, and the saturation induction increased by a maximum of about 15 % at a dose of N⁺ ion implantation of about 5 x 10¹⁶ ions/cm² , namely at an average density of nitrogen of about 12 at.%. When the average density of nitrogen exceeded the above-mentioned value, the saturation induction rapidly decreased and fell to the same level as that of an iron film at an average density of nitrogen of 20 at.%. It will be understood from the above results that the saturation induction increases in a range of average density of nitrogen ranging from 0 at.%. to 20 at.% exclusive, favorably in a range of an average density of nitrogen ranging from 5 at.% to 18 at.%. Figs. 11(a) and (b) roughly illustrate a process for preparing a perpendicular magnetic recording head using as the main pole a magnetic layer having a high saturation induction as mentioned above. As shown in Fig. 11(a), a thin iron film 12 having a thickness of 0.15 µm was deposited as the main pole layer on a non-magnetic substrate 11 of Fotoceram (trade name of glass-ceramic products manufactured by Corning Glass Works, U.S.A.) by sputtering to form a pattern of a head having a tip portion of the magnetic pole with a width so narrowed as to provide a predetermined track width. Thereafter, a nitrogen ion implantation was made into the thin iron film 12 at a density of 5 x 10¹⁶ ions/cm². Subsequently, the substrate was heated at 350 o C for 30 minutes to eliminate the strain caused by the ion implantation and at the same time to stabilize a phase showing a high saturation induction. Thus a main pole layer 12 having a high saturation induction was prepared. As shown in Fig. 11(b), a layer 13 of Permalloy for reducing the magnetic resistance of the main pole layer 12 was formed on the main pole layer 12, followed by patterning to remove part of the Permalloy layer 13 close to the tip of the main pole layer 12 by a width of about 2 - 5 µm. Subsequently, an insulating layer 14 of SiO₂ having a thickness of about 3 µm was formed all over by sputtering. An Aℓ film was deposited on the layer 14 through a mask by vacuum deposition to form a spiral Aℓ winding 15 having a width of 6 µm, a height of 4.0 µm, and a predetermined number of turns. Subsequently, a resin layer 16 was so coated as not only to fill up the gaps between the turns of the winding but also to cover the top surfaces, followed by curing thereof. An auxiliary pole 17 of a Co-W-Zr amorphous magnetic alloy film was formed on the layer 16. Fig 12 shows a plan view of a perpendicular magnetic recording head thus prepared, wherein reference numeral 11 stands for a non-magnetic substrate, 17 for an auxiliary pole, 15 for a winding, 18 for a lead wire portion of the winding 15, and 19 for a surface facing a recording medium. In recording on a Co-Cr perpendicular magnetic recording medium having a coercive force Hc of 8.10⁴ Am⁻¹ (1,000 Oe), use of the magnetic head prepared in this Example provided an increase of about 30 % in recording density D₅₀ (recording density at which the playback output is half the output at a low recording density) over a magnetic head having a main pole not ion-implanted. As described above, it was confirmed that the magnetic head according to the present invention improved the recording density by virtue of the high saturation induction given by ion implantation to the main pole. The improvement of recording density as in the case of nitrogen ion implantation was recognized in the case where either of carbon and boron ions were implanted, instead of nitrogen ions, into a main pole of iron or an iron-based magnetic alloy. Example 2 In a magnetic head having a thin magnetic layer as described in Example 1, it is important to control the magnetic anisotropy of the thin magnetic layer. In general, the thin magnetic layer has a tendency that the permeability in the direction perpendicular to the direction of easy magnetization is higher than that in the direction of easy magnetization. Therefore, it is preferred to have the direction perpendicular to the direction of magnetic flux coincide with the direction of easy magnetization in the constitution of the magnetic head. In preparing the magnetic head according to the present invention, the magnetic anisotropy of the main pole can be controlled by conducting ion implantation while applying the magnetic field. In this Example, ion implantation was carried out while applying a magnetic field of 4 x 10³ Am⁻¹ (50 Oe) in the direction of the track width of the main pole, namely in the direction A shown in Fig. 12. The ion implantation conditions other than the magnetic field application were the same as in Example 1. Thereafter, a magnetic head for perpendicular magnetic recording was prepared in the same manner as in Example 1. Using the magnetic head, recording was made on a Co-Cr perpendicular magnetic recording medium as used in Example 1. The playback output at this time was higher by about 2 dB than that in the case of a magnetic head prepared without application of any magnetic field to the main pole layer during ion implantation. As described above, it was confirmed that an effect can be attained if the anisotropy of a main pole layer is controlled by applying a magnetic field in the step of ion implantation. Example 3 Figs. 13(a) to (g) diagrammatically illustrate a process for preparing a magnetic head consisting of Mn-Zn ferrite and a sputtered film of an iron-based magnetic alloy according to this invention, which is used as a magnetic head for longitudinal magnetic recording. The magnetic head of this Example has a structure described in Japanese Laid-Open Patent Publication No. 58-1551513 (1983). As shown in Fig. 13(a), two Mn-Zn ferrite substrate 21 were prepared. A pair of contiguous V grooves 24 were formed by, for example, grinding, between every two flat portions 23 left at predetermined intervals on the surface 22 of one substrate which was supposed to be a gap confronting surface. In this case, the top of the inverse V protrusion 25 of the substrate 21 between every pair of the contiguous V grooves 24 was set to be lower by a predetermined length than the flat portions 23. As shown in Fig. 13(b), an iron film 26 having a thickness of about 10 µm was formed by sputtering on the side 22 of the substrate 21 subjected to the groove-forming operation. As shown in Fig. 13(c), a low melting point glass layer 27 is melt-formed so as to at least fill up the V grooves 24 on the iron film 26 deposited on the substrate 22. As shown in Fig. 13(d), the glass layer side of the substrate 21 with a glass layer 27 was ground and polished up to the height of the flat portions 23. At this time, the iron film 26 on the top of every inverse V protrusion 25 of the substrate 21 was partially ground and polished to become flat. Thus, planes 28 forming a functional gap and having a predetermined track width were obtained. As shown in Fig. 13(e), a groove 29 for a winding window was formed by, for example, grinding, in the substrate 21 subjected to the step of Fig. 13(d) on the side thereof having the iron film 26 perpendicularly to the V grooves 24. Thus a block 30 of a half body of a magnetic head core was prepared. A substrate 21 as shown in Fig. 13(d) was prepared from another Mn-Zn ferrite substrate 21, and used as a block 30' of a half body of the magnetic head core. Subsequently, nitrogen ions were implanted into portions 31 of the iron film of the functional gap-forming planes 28 of the magnetic head core half-body block 30 on the side adjacent to the functional gap and the corresponding portions of the iron film of the magnetic head core half-body block 30' at a density of 5 x 10¹⁶ ions/cm². Thereafter, a SiO₂ film having a thickness of 0.15 µm was deposited as the gap-forming layer by sputtering on the functional gap-forming plane of each of the magnetic head core half-body block 30 and 30'. As shown in Fig. 13(f), the magnetic head core half-body blocks 30 and 31' subjected to the step of Fig. 13(e) were abutted against each other through the gap-forming layers with the ion-implanted portions of the iron film being confronted with each other, and heated at 380 o C for 30 minutes to melt the glass layers 27 for bonding the same. Thus the magnetic head core half-body blocks 30 and 30' were bonded with each other to effect integration. This heating also was intended to strengthen the bonding of nitrogen implanted into the iron film with iron for stabilizing the magnetic layer having a high saturation induction. Subsequently, a magnetic head 32 as shown in Fig. 13(g) was obtained by cutting the integrated magnetic head core half-body blocks 30 and 30' along dot-dash lines. The head 32 included the functional gap 33. For comparison, a magnetic head as shown in Fig. 13(g) was prepared in substantially the same manner as described above except that ion implantation was not made into a magnetic head core half-body block 30 having a groove 27 for a winding window as shown in Fig. 13(e) and a magnetic head core half-body block 30' having no groove for a winding window. Using each of these magnetic heads, a signal of 5.8 µm in wavelength was recorded on a metal tape having a coercive force Hc of 12.10⁴ Am⁻¹ (1,500 Oe). When the signal was played back using a conventional ferrite magnetic head, it was recognized that the magnetic head prepared by involving the step of ion implantation provided an output increase of about 1.5 dB over the magnetic head prepared without the step of ion implantation. Such a recording characteristics-improving effect also could be obtained in the case where carbon or boron ion implantation was conducted in place of nitrogen ion implantation. As hereinbefore described, introduction of at least one element selected from among nitrogen, carbon, and boron by ion implantation into the main pole film in a portion thereof in close proximity with the surface facing a magnetic recording medium in the case of a magnetic head for perpendicular magnetic recording, and into iron or an iron-based alloy, used on the side of the functional gap-forming plane, at least in a portion thereof in close proximity to the functional gap in the case of a magnetic head for longitudinal magnetic recording served to improve the saturation induction of the iron or iron-based alloy to provide a magnetic head having excellent recording characteristics.

Claims: A process for preparing a magnetic layer comprising the steps of implanting ions into the surface region of a thin transition element-based magnetic film (1;3;12;26) and annealing said film to form an ion-diffused layer to thereby control the composition of said surface region for forming a desired magnetic compound layer. A process for preparing a magnetic layer as claimed in claim 1, wherein said ions are implanted by multiple ion implantation while changing ion acceleration voltages to provide a single composition for said desired magnetic compound layer. A process for preparing a magnetic layer as claimed in claim 1 or 2, wherein said steps of ion implantation and annealing are repeated after deposition of said thin transition element-based magnetic film to provide a multi-layer structure for said desired magnetic compound layer. A process for preparing a magnetic layer as claimed in any one of cliams 1 to 3, wherein said ions are implanted in a selected area or areas of the surface of said thin transition element-based magnetic film, and the resulting magnetic film is annealed to control the composition in said selected area or areas of the surface of said resulting magnetic film to provide a desired magnetic compound area or areas. A process for preparing a magnetic layer as claimed in any one of claims 1 to 4, wherein said transition element mainly constituting said thin transition element-based magnetic film is at least one of Fe, Co and Ni. A process for preparing a magnetic layer as claimed in any one of claims 1 to 5, wherein a plurality of said magnetic layers is formed through the steps of deposition of thin magnetic films ion implantation and annealing of said films and intermediate deposition of at least one non-magnetic layer. A process for preparing a magnetic layer as claimed in any one of claims 1 to 6 wherein said annealing is at a temperature of 500°C or lower. A process for preparing a magnetic layer as claimed in any one of claims 1 to 7 wherein thin film is subjected to ion implantation while there is applied a one-directional magnetic field inside said film or a magnetic field rotating relative to said film inside said film. A magnetic head comprising a magnetic pole formed at a portion at least on one side thereof which in use is to be in close proximity to a magnetic recording medium, in an thin iron or iron-based alloy film (1;3;12;26) having at least a portion thereof constituting a region containing at least one element ion-implanted and annealed therein, said element or elements being selected from nitrogen, carbon and boron. A magnetic head as claimed in claim 9, wherein said region containing at least one element selected from nitrogen, carbon and boron has an average density of said at least one element of less than 20 at.%. A magnetic head as claimed in claim 9, wherein said region containing at least one element selected from nitrogen, carbon and boron has an average density of said at least one element of 5 to 18 at.%.

Inventors: IMURA, RYO, KUMASAKA, NORIYUKI, OTOMO, SHIGEKAZU, SUGITA, YUTAKA, SUZUKI, RYO
Applicants: HITACHI, LTD.
Application year: 1985
Main classification: G11B5
IPC codes: G11B5, H01F41