MAGNETIC HEAD HAVING A LAYER STRUCTURE

Abstract: Magnetic head (1) having a head face (3) and a layer structure (7) comprising a first magnetic layer (13a, 13b), a second magnetic layer (17) and a thin insulation layer (19a, 19b) electrically separating these magnetic layers. At least the first layer of these magnetic layers comprises an amorphous cobalt alloy and is an integral part of the first magnetic layer comprising the amorphous cobalt alloy.

Description: Magnetic head having a layer structure. The invention relates to a magnetic head having a head face and a layer structure comprising a first magnetic layer, a second magnetic layer and an insulation layer electrically separating said magnetic layers, at least the first layer of said magnetic layers comprising an amorphous cobalt alloy. A magnetic head of this type is known from US-A 5,284,572 (PHN 13.265). The known magnetic head, which is of the thin-film type, comprises a soft-magnetic layer functioning as a flux-guiding element and a magnetoresistive layer extending opposite an interruption of the flux-guiding element and functioning as a transducing element. An insulation layer of SiO , which serves to electrically insulate the flux-guiding element from the transducing element, is present between these two layers. The insulation layer formed by deposition on the flux-guiding element has a relatively large thickness of, for example, 400 nm so as to achieve the desired insulation. A drawback of the presence of such a relatively thick insulation layer is that, during operation, a part of the magnetical information supplied by the flux-guiding element does not reach the transducing element but, due to the barrier caused by the insulation layer, traverses a path which does not extend through the transducing element. Of course, this has a detrimental effect on the efficiency of the magnetic head. It is an object of the invention to give the insulation layer in the magnetic head described in the opening paragraph a thinner structure. To achieve this object, the magnetic head according to the invention is characterized in that the insulation layer comprises an oxide of cobalt from the amorphous cobalt alloy. It has been found by experiment that such an insulation layer may have such good dielectric properties and have such a homogeneous structure that already at a relatively small thickness, of the order of 10 to 100 nm, the required electrical resistance is present between the magnetic layers. In one embodiment, the insulation layer is an integral part of the first magnetic layer. An embodiment of the magnetic head according to the invention is characterized in that the amorphous cobalt alloy is a CoNbZr alloy, particularly Co 8 NB 9 Zr 3 . It has been found that, when using a magnetic layer of a CoNbZr alloy, an insulation layer of CoNbZrO, which mainly comprises one or more oxides of cobalt, can be realized in a simple manner during manufacture. This will be elucidated in the description hereinafter. An embodiment of the magnetic head according to the invention is characterized as defined in claim 4. In such a magnetic head, implemented in practice as a thin-film magnetic head, the distance between the magnetoresistive element (MR element) and the flux guide may be relatively small, for example, of the order of 50 nm. A small distance between the MR element and the flux guide enhances the magnetic coupling between the MR element and the flux guide so that also a further object of the invention, namely providing a magnetic head having an enhanced efficiency, is achieved. The magnetic head according to the invention is eminently suitable as a read head in a recording system. An embodiment of the magnetic head according to the invention is characterized as defined in claim 5. A magnetic head having such a structure is generally known by the name of sandwich head. Sandwich heads may be used in magnetic recording and/or reproducing systems. Magnetic layers of an amorphous cobalt alloy have satisfactory soft-magnetical properties, such as a high saturation magnetization, a low coercivity, a low magnetostriction and a high permeability. The insulation layers used in the magnetic head according to the invention are provided with a high-ohmic oxide or high-ohmic oxides and have a relatively small thickness, for example, of the order of 100 nm. Consequently, there is an effective electrical barrier between the consecutive magnetic layers, so that eddy currents are suppressed effectively, and a compact stacking of magnetic layers is possible. The invention also relates to a method of manufacturing a layer structure comprising a first magnetic layer, an insulation layer and a second magnetic layer. Such a method is known from the above-mentioned US-A 5,284,572 and is used in the manufacture of the magnetic head described in the opening paragraph. In the known method, a first magnetic layer is formed by deposition of NiFe, whereafter an insulation layer is provided on this magnetic layer by means of deposition of an electrically insulating material, particularly SiO . Subsequently, a magnetoresistive layer is provided by means of deposition on the insulation layer supported by the first magnetic layer. In the known method, several but essentially different deposition steps, namely deposition steps for forming the magnetic layers and a different deposition step for providing the insulation layer are therefore necessary. It is an object of the invention to improve and simplify the known method. To achieve this object, the method according to the invention is characterized in that a first magnetic layer is formed by deposition of an amorphous cobalt alloy, whereafter this layer is exposed to an oxidizing ambience for forming a layer comprising an oxide of cobalt, whereafter a second magnetic layer is formed by deposition of a magnetic material on the formed oxide layer. In this method, the oxide of cobalt is simply formed by introducing it into an oxidizing ambience after the magnetic layer has been provided. The insulation layer thus formed can be considered as an integral part of the first magnetic layer comprising the amorphous cobalt alloy. It is often preferred to form the magnetic layers by means of sputtering in a sputtering system, in which the same target can be used every time if the same cobalt " alloy, preferably a CoNbZr alloy, is used in each magnetic layer. The formation of the oxide of cobalt can then take place in the sputtering system used by, for example, supplying oxygen or by using plasma oxidation or reactive sputtering of the target with oxygen as a reactive gas. Both plasma oxidation and reactive sputtering are known techniques. A related variant of the method according to the invention is defined in claim 7. The invention also relates to a device for writing and/or reading information by means of a magnetic head into or from a magnetic recording medium. This device may be of a known type, in which the recording medium is disc or tape-shaped but in which the magnetic head according to the invention is used. A known device is described and shown, for example, in PCT application WO 97/24712 (herein incorporated by reference). With reference to the claims, it is to be noted that various combinations of the characteristic features defined in the dependent claims are possible. These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings: Fig. 1 is a diagrammatic cross-section of a first embodiment of the magnetic head according to the invention, Fig. 2 is a diagrammatic, perspective elevational view of a second embodiment of the magnetic head according to the invention, and Fig. 3 is an elevational view, according to arrow III, of a part of the second embodiment on a larger scale. The magnetic head 1 according to the invention, shown in Fig. 1, is implemented as a thin-film magnetic head and has a head face 3. The magnetic head 1 comprises a substrate 5, a layer structure 7 present on the substrate 5 and a protective block 9 present on the layer structure 7. The layer structure 7 is provided with an insulating basic layer 11 of, for example, SiO 2 or Al 2 O 3 , which is provided on the substrate 5 of a magnetically conducting material such as an NiZn ferrite. The layer structure 7 is further provided with a first magnetic layer 13a, 13b, a first layer part 13a of which bounds the head face 3 and a second layer part 13b is spaced apart therefrom, while a gap or slit 15 filled with a nonmagnetic, non-electrically conducting material such as SiO 2 extends between the two layer parts 13a and 13b. The first layer part 13a constitutes a first flux guide adjacent to the head face and a second layer part 13b constitutes a second flux guide. The gap 15 between both flux guides 13a and 13b is bridged by a magnetoresistive element (MR element) which is formed or is also formed by a second magnetic layer 17. The first magnetic layer 13a, 13b, as well as the second magnetic layer 17, are formed from an amorphous cobalt alloy, notably a CoNbZr alloy, in this embodiment. An insulation layer 19a, 19b electrically separating both magnetic layers 13a, 13b and 17 from each other extends between the first magnetic layer 13a, 13b and the second magnetic layer 17. The insulation layer 19a, 19b comprises an oxide of cobalt from the amorphous cobalt alloy of the first magnetic layer 13 a, 13b. The magnetic head 1 shown in Fig. 1 is manufactured by using an embodiment of the method according to the invention, in which the first magnetic layer 13a, 13b is formed on the basic layer 11 by means of sputtering deposition of the amorphous cobalt alloy in a sputtering system, whereafter this layer 13a, 13b is exposed to an oxidizing ambience for forming an oxide of cobalt, resulting in the insulation layer 19a, 19b which is thereby an integral part of the first magnetic layer 13a, 13b. In this embodiment, the insulation layer 19a, 19b has a thickness of 50 nm. After the insulation layer 19a, 19b has been formed, the gap 15 is filled with a non-magnetic, non-conducting material, in this embodiment SiO 2 , whereafter the second magnetic layer 17 is formed by means of sputtering deposition of a soft-magnetic material, the amorphous cobalt alloy in this embodiment. Subsequently, this layer 17 is provided with a layer 21 of an insulating material, SiO in this embodiment, on which the protective block 9 is placed. Subsequently, the head face 3, which may be flat or curved, is formed by, for example, polishing and/or lapping. Note that the electric input and output conductors are not shown in the drawing. It is further noted that the magnetic head may be implemented as a one-channel or a multichannel head. The magnetic head may be implemented for co-operation with a tape-shaped recording or information medium, particularly a magnetic tape, or for co-operation with a disc-shaped recording or information medium, particularly a magnetic disc or a magneto-optical disc. The magnetic head 101 according to the invention, shown in Figs. 2 and 3, is a sandwich head. Sandwich heads are used in systems for magnetically writing and/or reading information, such as video tape systems. The magnetic head 101 has two ceramic substrates 103a, 103b and 105a, 105b, a stack 107 of different layers placed between the substrates 103a, 103b and 105a, 105b, and a coil 109 as a transducing element. In this embodiment, the substrates are made of CaTiO 3 . The stack 107 is a layer structure comprising a magnetic layer 107 of an amorphous cobalt alloy alternating with an insulation layer 107b of an oxide of cobalt from the amorphous cobalt alloy. The magnetic layers 107a are responsible for the transport of magnetic flux and should therefore have satisfactory soft-magnetical properties such as a high saturation magnetization, a low coercivity and a low magnetostriction. Moreover, the permeability should be sufficiently high through a wide frequency range. It is known per se that CoNbZn alloys are suitable materials for this purpose. It is further known to make use of rotation permeability so as to achieve a high permeability through a wide frequency range, in which case the required domain orientation of the magnetic domains in a layer of CoNbZn alloy can be achieved by using a magnetic field during sputtering or by annealing the soft-magnetic material. The insulation layers 107b which are present serve to inhibit eddy currents which could reduce the permeability. It has been found that the insulation layers 107b of an oxide of cobalt from the alloy which is present have a sufficiently high electrical resistance to allow formation of insulated laminations so that eddy currents are effectively inhibited. The magnetic head 101 has a head face, in this embodiment also a contact face, 111 for co-operation with a magnetic tape which, during operation, moves across the head face 109 in the direction denoted by arrow x. The following remarks may be made with reference to the manufacture of the magnetic head 101, particularly its stack 107. The invention provides the possibility of realizing an increase of the production output, if both the soft-magnetic layers 107a and the insulation layers 107b are formed by means of sputtering, in which both sputtering processes are performed in one and the same sputtering apparatus. In this respect, an advantageous method of forming all layers 107a and 107b starts from the same CoNbZr target. In a first step of a first method, CoNbZr is deposited by means of sputtering so as to form a soft-magnetic layer 107a. In a second step, plasma oxidation is used, in which mainly cobalt oxidizes and CoNbZrO is formed so as to form a first insulation layer 107b. The first and second steps are subsequently repeated as often as is necessary to obtain the desired number of layers 107a and 107b of the stack 107. A suitable target is, for example, a target of Co 88 Nb Zr 3 alloy. Experiments performed in a plasma oxidation method proved that RF powers of, for example, 100 W and 200 W at an oxygen pressure of 0.8 Pa are suitable for realizing the high-ohmic insulation layers 107b. The oxidation time was 10 minutes. It was also found that, in these experiments, the magnetical properties such as coercivity of the soft-magnetic layer or layers 107a which are present are not influenced or are hardly influenced detrimentally. In a second method, CoNbZr is deposited by means of a first sputtering process using a sputtering clock so as to form the soft-magnetic layers 107a, and reactive sputtering with oxygen takes place in a second sputtering process so as to form the insulation layers 107b. Experiments proved that a sputtering rate of 10 nm/min is possible at an RF power of 500 W. The experiments further proved that the CoNbZrO formed does not have any detrimental influence on the magnetical properties of the CoNbZr alloy already present. In a practical embodiment, the thickness of the magnetic layers 107a was 2500 nm each and the thickness of the insulation layers 107b was 100 to 200 nm each. The total number of magnetic layers 107a in the stack is usually 10 to 25 in practical embodiments. It is to be noted that the invention is not limited to the embodiment shown. Also types of magnetic heads other than the ones shown such as, for example, magnetic heads having giant-magnetoresistive elements and magnetic heads used as sensors, particularly of the thin-film type, fall within the scope of the invention.

Claims: CLAIMS: 1. A magnetic head having a head face and a layer structure comprising a first magnetic layer, a second magnetic layer and an insulation layer electrically separating said magnetic layers, at least the first layer of said magnetic layers comprising an amorphous cobalt alloy, characterized in that the insulation layer comprises an oxide of cobalt from the amorphous cobalt alloy. 2. A magnetic head as claimed in claim 1, characterized in that the insulation layer is an integral part of the first magnetic layer. 3. A magnetic head as claimed in claim 1, characterized in that the amorphous cobalt alloy is a CoNbZr alloy. 4. A magnetic head as claimed in claim 1 , characterized in that the first magnetic layer comprising the amorphous cobalt alloy is a flux guide adjacent to the head face, and the second magnetic layer is a magnetoresistive transducing element, while the insulation layer comprising the oxide of cobalt extends between the flux guide comprising the amorphous cobalt alloy and the magnetoresistive transducing element. 5. A magnetic head as claimed in claim 1 , characterized in that the layer structure comprises a stack of magnetic layers sandwiched between two substrates, in which two consecutive layers each time constitute an assembly of the first magnetic layer comprising the amorphous cobalt alloy, the insulation layer comprising the oxide of cobalt and the second magnetic layer, said magnetic head being provided with an inductive transducing element surrounding at least a part of the substrates and of said stack. 6. A method of manufacturing a layer structure, wherein a first magnetic layer is formed by deposition of an amorphous cobalt alloy, whereafter this layer is exposed to an oxidizing ambience for forming a layer comprising an oxide of cobalt, whereafter a second magnetic layer is formed by deposition of a magnetic material on the formed oxide layer. 7. A method of manufacturing a layer structure, wherein a first magnetic layer is formed by sputtering deposition from a target of an amorphous cobalt alloy, whereafter an oxide for forming an insulation layer is deposited from the same target on said layer by means of reactive sputtering. 8. A device for writing and/or reading information into or from a magnetic recording medium, which device is provided with a magnetic head as claimed in any one of claims 1 to 5.

Inventors: KLAASSENS WILCO, KUIPER ANTONIUS E T, KLAASSENS, WILCO, KUIPER, ANTONIUS, E., T.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2000
Main classification: G11B5
IPC codes: G11B5