Magnetic multilayer structure

Abstract: A magnetic multilayer structure (14) having an increased permeability and an increased saturation magnetic flux density comprises a plurality of magnetic layers (12) and a plurality of intermediate layers (13) alternately laminated one upon another. Each of the magnetic layers (12) is made of Fe, Co, Ni or an alloy containing one of Fe, Co and Ni, while each of the intermediate layers (13) is made of a material capable of interstitially forming a solid solution with the material of the magnetic layers (12).

Description: The present invention relates to a multilayer magnetic structure as defined in the preamble of the claim 1 and to a magnetic head defined in the preamble of the claim 8. A multilayer magnetic structure and a magnetic head of the said type are known from EP 0 174 144 A3. There it is disclosed that ion implantation is conducted in a desired area of the surface of a magnetic layer and that annealing of the said layer is carried out to control the composition in that desired area. To facilitate the control of the composition a one-directional or rotating magnetic field may be applied during ion implantation. To obtain ion-implanted layer having a thickness of more than 1 µm a lamination process is used interposing ferromagnetic or non-magnetic intermediate layers between ion-implanted layers. In preparing a magnetic head a portion of a magnetic pole one side of which is in close proximity to a magnetic recording medium is formed into an iron or iron-based magnetic alloy film a part of which is subjected to ion implantation and annealing. It is a common technique to make a magnetic layer constituting a magnetic pole of a magnetic head for magnetically recording using an alloy containing Fe, Co or Ni as a main component. An example for a magnetic layer like that is known from JP 59-182 938 A. For high density recording both a high relative permeability and a low coercive force of the magnetic material used are required. With the hitherto known materials, however, it is extremely difficult to form a magnetic layer having both the characteristics of a high saturation magnetic flux density and of a high relative permeability. Particularly, though there is a tendency such that the relative permeability increases with a decrease in coercive force, the saturation magnetic flux density does not always increase and almost all of the hitherto known multilayer structures have a faily lower saturation magnetic flux density than that of a single layer of Fe. Therefore, it is an object of the present invention to provide a magnetic structure which has both a high saturation magnetic flux density and a high permeability and particularly to improve or increase the relative permeability of the material without reducing its saturation magnetic flux density. According to the present invention the said object is achieved by a multilayer magnetic structure as defined in the claim 1. Advantageous developments of the invention and a preferred embodiment of a magnetic head are defined in further claims. When a multilayer structure is formed by laminating Fe layers through other elements according to the present invention, as investigations have shown, there is a tendency such that the coercive force decreases. Moreover, observations using an electron microscope have proved that the crystal grain of the Fe layer is cut by the intermediate layer and is changed from the columnar crystal to the fine crystal grain, which presumably is one of the reasons of the reduction of the coercive force obtained. As to the increase of the relative permeability as obtained by using elements selected according to the present invention without reducing the saturation magnetic flux density of the multilayer structure it has its main reason in the capability of the said elements to interstitially form a solid solution with an alloy containing iron group metal as a main component. Additionally, the said elements may be presumed to have a nature to make the crystal grain fine without diluting the magnetic moment per unit volume of the iron group metal or an alloy thereof. A multilayer magnetic structure according to the present invention may show a saturation magnetic flux density of 15 x 10⁻⁵ Vs/cm² or higher, a relative permeability of 1000 or higher and a coercive force of about 80 A/m or lower. In the magnetic multilayer structure according to an embodiment of the invention, the magnetic layer is made of a single metal consisting of Fe, Co or Ni having a high saturation magnetic flux density, an alloy containing at least one kind selected from these metals, an alloy containing as a main component the metal selected from the group of these metals and an element selected from the group of C, Si, B, N, Ti. The intermediate layer which is laminated onto the magnetic layer is made of a single element selected from the group of B, C, N, P, S capable of interstitially forming a solid solution with the metal or alloy constituting the magnetic layer or a compound containing at least one kind of element selected from the group of B, C, N, S, P. The sum of the thicknesses of the magnetic layer and intermediate layer thereon in the magnetic multilayer structure formed by laminating these layers is preferably within a range from 0.2 nm to 250 nm. A thickness of intermediate layer is preferably within a range from 0.05 nm to 5 nm. It is also desirable that a thickness of intermediate layer is in a range from 1% to 25% of a thickness of one period in the magnetic multilayer structure. A thickness of the magnetic multilayer structure formed by laminating one or more periods each consisting of a magnetic layer and an intermediate layer largely differs in dependence on the specifications of the magnetic pole of a magnetic head or the like to be manufactured. The thickness of this magnetic pole largely changes to about 100 nm to 50 µm. A group IV element selected from the group of Ti, Zr, C, Si, Ge, Sn, etc. or an element such as C, N, B, P, S, capable of interstitially forming a solid solution with the Fe, Ni or Co layer is contained as an additive into the alloy forming the magnetic layer, thereby enabling the permeability of the magnetic multilayer structure to be increased. A group VIII element selected from the group of Rh, Ru, Pd, Co, Ni, Os, Ir and Pt or a group I element selected from the group of Cu, Ag and Au is contained as an additive into the alloy forming the magnetic layer, thereby enabling the corrosion resistance of the magnetic multilayer structure to be improved. By containing Ti, Zr, Hf, V, Nb, Ta, Mo or W as an additive, the heat resistance of the magnetic multilayer structure can be improved. The amount of the additive should be set such that the absolute value of the magnetostriction constant of the magnetic layer is substantially 1 x 10⁻⁶ or lower. Due to this, a distortion which is caused in the manufacturing process of the magnetic multilayer structure and in the process to make a magnetic head using the magnetic multilayer structure, for example, a distortion which is caused by a formation or patterning of the layer is minimized, so that a deterioration of the magnetic characteristic of the head can be prevented. It is desirable that an amount of the additive does not generally exceed 10 atomic %. The magnetic multilayer structure of the invention can constitute one or both of two magnetic layers which form a magnetic pole of a magnetic head for the high density longitudinal recording shown in Fig. 7 or a magnetic layer forming the main magnetic pole of a magnetic head for the high density perpendicular magnetic recording shown in Fig. 8. According to an embodiment, a magnetic layer made of a single metal of Fe, Co or Ni or an alloy containing as a main component the element selected from these elements is finely laminated through an intermediate layer containing an element capable of interstitially forming a solid solution with the foregoing metal or alloy, thereby forming a magnetic multilayer structure. This multilayer structure has a high saturation magnetic flux density about, e.g., 1,8 T or higher and a high relative permeability about 1500 or higher. Therefore, when this multilayer structure is used as a magnetic layer constituting the main magnetic pole of a magnetic head for the magnetic recording, a strong magnetic field can be generated from the tip of the magnetic pole without causing a magnetic saturation even if a thickness of layer is made so thin as to be about 0.2 µm. A super high density magnetic recording can be accomplished. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagrammatical view showing a cross sectional structure of a magnetic multilayer structure produced in the Example 1 according to the present invention. Fig. 2 is a diagrammatical view showing a structure of an ion beam sputtering apparatus for use for processing an embodiment of the invention. Fig. 3 is a graph showing an influence by the ratio of a carbon layer thickness to one period thickness in a magnetic multilayer structure which exerts on the relative permeability and coercive force of the magnetic multilayer structure. Fig. 4 is a graph showing an influence by the ratio of a carbon layer thickness to one period thickness in a magnetic multilayer structure. Fig. 5 is a graph showing the relation between the one period thickness in a magnetic multilayer structure and the saturation flux density of the magnetic multilayer structure. Fig. 6 is a graph showing the relation between the one period thickness in a magnetic multilayer structure and the relative permeability of the magnetic multilayer structure. Figs. 7 and 8 are diagrams showing examples of a magnetic head for the longitudinal recording and a magnetic head for the perpendicular recording. DESCRIPTION OF THE PREFERRED EMBODIMENTS (Example 1) A magnetic multilayer structure was formed by an ion beam sputtering method. As shown in Fig. 2, according to the ion beam sputtering method, accelerated ions emitted from a first ion gun 1 sputter a target material 4 set in a rotary target holder 3, thereby allowing sputtering particles to be deposited onto a base plate 8 attached onto a base plate holder 7. At this time, since the target holder 3 is rotated at every predetermined period of time, target materials 4 and 5 which are respectively fixed one by one onto the front and back surfaces of the target holder 3 are sputtered by the ions. Since the sputtering particles are alternately deposited onto the base plate 8, a thin layer is laminated. In this Example, a second ion gun 2 to irradiate ions onto the base plate holder 7 was also used. The second ion gun 2 can perform not only the cleaning of the base plate 8 just before the sputtering but also the ion irradiation onto the base plate 8 even during the sputtering operation by the first ion gun 1. By exciting the sputtering particles, the state of the layer to be deposited onto the base plate 8 can be controlled so as to optimize the magnetic characteristic of the magnetic multilayer structure. The desirable ion beam sputtering conditions to form a multilayer structure having a high saturation magnetic flux density and a high relative permeability were as follows. The forming speeds of the Fe layer and C layer were respectively independently measured under the above conditions. The thickness of layer when forming a multilayer structure was controlled by the time. In this case, the layer forming speed of Fe was 0.22 nm/sec and that of C was 0.07 nm/sec. When forming a multilayer structure, first, the operation of the first ion gun was started and the presputtering processes of the Fe and C targets were performed with a shutter (not shown) closed. Next, the operation of the second ion gun was started. Thereafter, the shutter was opened and formation of a multilayer structure was started. In this Example, by rotating from the Fe target to the C target and from the C target to the Fe target each time a predetermined period of time has elapsed, a magnetic multilayer structure having a structure shown in Fig. 1 was formed. Namely, the magnetic multilayer structure is formed by laminating a plurality of periods on the base plate 11, wherein each period consists of a combination of the magnetic layer 12 made of, e.g., Fe and the intermediate layer 13 made of, e.g., C. Fig. 3 shows a relative permeability µ′ and a coercive force H c at 5 MHz of the resultant magnetic multilayer structure and Fig. 4 shows a saturation flux density B s . As will be obvious from Fig. 3, the coercive force greatly decreased with an increase in the ratio of the single carbon layer thickness to the one period thickness. The relative permeability greatly increased with the reduction of the rate. Although there is a tendency such that the relative permeability decreases as the ratio of the carbon layer thickness further increases, a change in coercive force did not occur. On the other hand, as will be obvious from Fig. 4, there is a tendency such that the saturation magnetic flux density gradualluy decreases with an increase of a single carbon layer thickness to one period thickness. However, a degree of the reduction of the saturation magnetic flux density is small until the ratio of 25% of the carbon layer thickness to one period thickness. When this ratio exceeds 25%, this reduction degree increases. From the foregoing results, one of the reasons why the saturation magnetic flux density decreases and the relative permeability increases by increasing the ratio of the carbon layer thickness is presumed as follows. Namely, the columnar crystal which is formed by a single iron layer is cut by interposing the thin carbon layer, thereby causing an effect similar to that the crystal grain diameter substantially decreases, so that the dispersion of the crystal line anisotropy was reduced. On the other hand, the reason why the saturation magnetic flux density decreases is because the ratio of iron to the multilayer structure decreases due to the insertion of carbon as a nonmagnetic material, so that the magnetic moment is diluted. However, it is presumed that when the ratio of the carbon layer thickness is small, a ferromagnetic Fe-C alloy is formed and the magnetic moment is not diluted. From the above results, the ratio of the single carbon layer thickness having the characteristics which are necessary as a magnetic pole material of the magnetic head such that the relative permeability is above 1000 and the saturation flux density is above 1.8 T is within a range from 1 to 25% of one period thickness. A more preferable ratio of the single carbon layer thickness is in a range from 2 to 20%. However, as shown in Figs. 5 and 6, when one period thickness as the sum of the thicknesses of the magnetic layer and intermediate layer forming the magnetic multilayer structure is less than 0.2 nm, the saturation magnetic flux density remarkably decreases. On the contrary, when one period thickness exceeds 50 nm, the relative permeability decreases. When one period thickness exceeds 250 nm, the relative permeability extremely decreases. Therefore, one period thickness is preferably set to be within a range from 0.2 nm to 250 nm, more preferably, in range from 0.2 nm to 50 nm. When the thickness of intermediate layer is less than 0.05 nm, the relative permeability remarkably decreases. When it exceeds 5 nm, the relative permeability again remarkably decreases. Thus, the thickness of intermediate layer is preferably set to be within a range from 0.05 nm to 5 nm. The resultant magnetic multilayer structure consisting of the iron layer having a thickness of 4.8 nm and the carbon layer having a thickness of 0.2 nm was examined by an X-ray diffracting method with a result that a diffracting line was detected at the position corresponding to a lattice plane distance d = 5.05 nm and the formation of the multilayer structure was confirmed. On the other hand, the resultant multilayer structure consisting of the iron layer having a thickness of 9.5 nm and the carbon layer having a thickness of 0.5 nm was analyzed by an Auger electronic spectrometer with a result that Auger electron intensities of iron and carbon alternately increased. Thus, the existence of the multilayer structure was also confirmed by the Auger electronic spectrometry. (Example 2) In the Example 1, a material of the magnetic layer, a material of the intermediate layer, and their thicknesses were changed as shown in Table 1 and the examinations were performed in a manner similar to the Example 1. Table 1 shows the saturation magnetic flux densities B s (T) and the relative permeabilities µ′ at 5 MHz of the magnetic multilayer structures obtained. As will be obvious from Table 1, all of the magnetic multilayer structures had saturation magnetic flux densities above 1,9 T and the relative permeabilities above 1500. These results show that the material of the magnetic layer is not limited to single iron but may be a material containing iron as a main component and that the material of the intermediate layer may be an element such as B, C, N, P, S capable of interstitially forming a solid solution with Fe or a compound containing these elements capable of interstitially forming a solid solution. As the material of the intermediate layer in Table 1, the material of the target when performing the ion beam sputtering has been shown. The multilayer structure obtained does not indicate that the layer containing the compositions shown in Table 1 was formed. The recording characteristic of the foregoing magnetic multilayer structure was examined in the case where this structure was used in the main magnetic pole of a magnetic head for the magnetic recording. Thus, it has been confirmed that the main magnetic pole of the magnetic head which can present the recording density above 39 kBPmm (kilobits/mm) (100 kBPI or kilobits/inch) larger than the conventional magnetic recording density of 3.1 kBPmm was obtained (80 kBPI). In the foregoing Examples, iron or iron alloy has been used as the magnetic layer. However, it has been confirmed that effects similar to those in the foregoing Examples can be also obtained even in the case of copper or nickel as the iron group element or an alloy containing this iron group element as a main component and the foregoing additive.

Claims: A multilayer magnetic structure, comprising a plurality of magnetic layers and a plurality of intermediate layers each of which is formed between two adjacent magnetic layers, characterised in that each of said magnetic layers is made of a magnetic material selected from the group consisting of Fe, Co, Ni and alloys containing at least one of said elements as a main component and that each of said intermediate layers is made of a single element selected from the group consisting of B, C, N, P and S or of a compound selected from the group consisting of ZrC, Fe₂B, TiB₂, BN, BP, B₄C, SiC, Si₃N₄, TiC, TiN, Ti₂N and AlN. A multilayer magnetic structure according to claim 1, characterised in that said alloys further contain an additive selected from the group consisting of C, Si, B, N and Ti. A multilayer magnetic structure according to claim 1, characterised in that the sum of the thicknesses of any of said magnetic layers and of an intermediate layer thereon is in the range from 0.2 nm to 250 nm, that each of said intermediate layers has a thickness in a range from 0.05 nm to 5 nm and that the ratio of the thickness of each intermediate layer to that of one period consisting of a combination of one magnetic layer and one intermediate layer is in a range from 0.01 to 0.25. A multilayer magnetic structure according to claim 1, charactrised in that the sum of the thicknesses of any of said magnetic layers and of an intermediate layer thereon is in a range from 0.2 nm to 50 nm, that each of said intermediate layers has a thickness in a range from 0.05 nm to 5 nm and that the ratio of the thickness of each intermediate layer to that of one period consisting of a combination of one magnetic layer and one intermediate layer is in a range from 0.01 to 0.25. A multilayer magnetic structure according to claim 1, characterised in that said alloy further contains an additive selected from the group consisting of a group IV element, N and B. A multilayer magnetic structure according to claim 1, characterised in that said alloy further contains an additive selected from the group consisting of a group VIII element, Cu, Ag or Au. A multilayer magnetic structure according to claim 1, characterised in that said alloy further contains an additive selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mo and W. A magnetic head having a magnetic pole portion, characterised in that at least a part of said magnetic pole portion is made of a multilayer magnetic structure as defined in claim 1.

Inventors: KOBAYASHI TOSHIO, KUMASAKA NORIYUKI, NAKATANI RYOICHI, OTOMO SHIGEKAZU, KOBAYASHI, TOSHIO, KUMASAKA, NORIYUKI, NAKATANI, RYOICHI, OTOMO, SHIGEKAZU
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1987
Main classification: G11B5
IPC codes: H01F10, G11B5