Magnetoresistance effect element and magnetoresistance effect sensor

Abstract: A magnetoresistance effect element includes a multilayer (4) obtained by stacking magnetic and nonmagnetic layers (2 and 3) to exhibit a magnetoresistance effect, and a reversal assist layer on formed in contact with the multilayer (4) to assist reversal of a magnetic moment of the magnetic layer.

Description: Present invention relates to a magnetoresistance effect element and a magnetoresistance effect sensor used in a magnetic field sensor, a magnetic head, and the like and, more particularly, to a magnetoresistance effect element and a magnetoresistance effect sensor utilizing an artificial lattice film. The magnetoresistance effect is an effect in which the resistance of an object is changed upon application of a magnetic field. Magnetoresistance effect elements that utilize this effect find a variety of applications including those for magnetic field sensors and magnetic heads because of their high sensitivity to magnetic fields and their ability to produce a relatively large output. While a Permalloy thin film is conventionally widely used for such magnetoresistance effect elements, the magnetoresistance ratio (ΔR/Rs: where ΔR is a difference in electric resistance between the zero magnetic field and the saturated magnetic field; Rs is the electric resistance obtained when the saturation field is applied) of a Permalloy film is as low as about 2 to 3% and, therefore, does not show a satisfactory sensitivity to changes in the magnetic field. On the other hand, as a new magnetoresistance effect element, a multilayer formed of alternately stacked magnetic and nonmagnetic layers each having a thickness of several to several tens of Angstroms or a so-called artificial lattice film has received a great deal of attention in recent years. Known types of the multilayers include (Fe/Cr) n (Phys. Ref. Lett. vol. 61(21) (1988)2472, (Permalloy/Cu/Co/Cu) n (J. Phys. Soc. Jap. vol. 59(9) (1990)3061), and (Co/Cu) n (J. Mag. Mag. Mat. 94(1991)L1; Phys. Rev. Lett. 66(1991)2152). These multilayers exhibit a high magnetoresistance ratio as scores of %. In particular, when these multilayers are formed by using a film formation apparatus comprising an ultra-high vacuum system, e.g., an ultra-high vacuum (UHV) vapor deposition and a molecular beam epitaxy (MBE), a high magnetoresistance effect exceeding 20% can be obtained at room temperature. Accordingly, when these multilayers are used in the magnetoresistance effect heads, a large increase in output is expected. However, a saturation field H S of the known multilayers are as strong as about 10 kOe in contrast to only several Oe for Permalloy. It follows that, where the known multilayers are used in a magnetic sensor or a magnetic head designed to detect a weak magnetic field, the magnetic sensor or head fails to exhibit a sufficient sensitivity. More specifically, when an application as a magnetic sensor or a magnetic head is considered, it is desirable for the artificial lattice film to exhibit a large magnetoresistance change under a weak magnetic field. To this end, the saturation field H S of the artificial lattice film is required to be diminished. However, an artificial lattice film meeting these particular requirements has not yet been developed. It is proposed to use a magnetoresistance effect head utilizing the magnetoresistance effect described above to read data recorded on a magnetic recording medium (IEEE MAG-7,150, (1971)). In recent years, as the size reduction and capacity increase of a magnetic recording medium have been in progress, the relative speed of the data reading magnetic head and the magnetic recording medium during data read has been decreased. Hence, a magnetoresistance effect head capable of obtaining a large output even at a low relative speed is expected. When a magnetoresistance effect head is to be put into practical use, two types of bias magnetic fields must be applied to this head. One bias magnetic field is generally called a transverse bias to be applied in a direction perpendicular to the sense current of the magnetoresistance effect element. The transverse bias is a magnetic field which is applied until the magnitude of an external signal and that of a detection signal reach a proportional state, i.e., a so-called operating point. An example of a method of applying the horizontal bias includes a self-bias scheme disclosed in Published Examined Japanese Patent Application Nos. 53-37205 and 56-40406 and the like and a shunt-bias scheme disclosed in Published Examined Japanese Patent Application No. 53-25646 and the like. According to the self-bias scheme, a soft adjacent layer is formed adjacent to a magnetoresistance effect film through a thin nonmagnetic film, and a magnetic field generated by the sense current is utilized as the transverse bias. A method of applying the transverse bias by flowing a current through a coil disposed adjacent to a magnetoresistance effect film is disclosed in Published Examined Japanese Patent Application No. 53-37206. A method of a hard magnetic film with a magnetization in one direction formed adjacent to a magnetoresistance effect film in order to apply the horizontal bias is disclosed in Published Examined Japanese Patent Application No. 54-8291 and the like. The other bias magnetic field is generally called a longitudinal bias to be applied in a direction parallel to the sense current of the magnetoresistance effect element. The longitudinal bias suppresses Barkhausen noise which is caused since the magnetoresistance effect element has a large number of magnetic domains. In other words, the longitudinal bias serves to minimize the number of magnetic walls which cause noise generation. Various methods have been conventionally proposed to apply the longitudinal bias. For example, U.S.P. No. 4,103,315 discloses that a uniform longitudinal bias is generated in a magnetoresistance effect film by exchange-coupling an antiferromagnetic film and a ferro-magnetic film. According to JOURNAL OF APPLIED PHYSICS VOL. 52,2472, (1981), when an FeMn alloy film is used as an antiferromagnetic film and a Permalloy (Ni 80 Fe 20 ) film is used as a magnetoresistance effect film, a vertical bias is applied to the magnetoresistance effect film due to the magnetic exchange coupling of the alloy and Permally films. In any of these cases, the spin of the magnetoresistance effect film is fixed in one direction by the longitudinal vertical bias to suppress the Barkhausen noise. As another example of the method of applying the vertical bias, in addition to the methods described above, a method of using an one-direction magnetized ferromagnetic film in the same manner as that employed for applying the transverse bias is proposed. According to this method, the longitudinal bias, the transverse bias, and an intermediate bias of the two biases can be applied by selecting the direction of magnetization. Magnetic Recording Laboratory, MR-37, the Institute of Electronic and Communication Engineers of Japan introduces a method of applying the longitudinal bias by forming a CoP film at the end portion of a yoke type magnetoresistance effect film. In this manner, various methods have been proposed to apply the longitudinal bias. When, however, these methods are applied to the magnetic head for hard disk drive, the following problems arise. Of these methods of applying the longitudinal bias, one with which the most preferable characteristics can be expected in an application to the magnetic head for hard disk drive is a method of forming an FeMn alloy (γ-FeMn alloy) film as an antiferromagnetic film on a magnetoresistance effect film made of a Permalloy or the like. The longitudinal bias magnetic field is desirably of 10 to 30 Oe. However, the FeMn alloy seriously adversely affects the reliability of the magnetoresistance effect element, as is reported in Nippon Kinzoku Gakkai (Japanese Metal Society) (543), fall 1990, since Mn is easily oxidized. When an antiferromagnetic film is to be formed by sputtering a γ-FeMn alloy, an α-FeMn alloy phase is sometimes formed, as is pointed out in JOURNAL OF APPLIED PHYSICS VOL. 52, 2471, (1981), and it is difficult to obtain a stable γ-FeMn alloy phase in the industrial level. Regarding the longitudinal bias to be applied, if it is weaker than the antimagnetic field at the edge portion of the magnetoresistance effect film, the magnetoresistance effect film fails to have a single magnetic domain; if it is weaker than this, the sensitivity of the magnetoresistance effect film is decreased. Hence, the longitudinal bias to be applied preferably has a strength to cancel the antimagnetic field at the edge portion of the magnetoresistance effect film. The strength of the antimagnetic field depends on the shape of the magnetoresistance effect element, i.e., the width and depth of the tracks, and the film thickness. Hence, the level of the exchange-coupling energy must be changed in accordance with the specifications of the magnetic head by controlling the shape of the magnetoresistance effect element. However, in order to control the exchange-coupling energy between the FeMn alloy as the antiferromagnetic film and the NiFe alloy as the magnetoresistance film, the thickness of the NiFe or FeMn alloy film must be changed, as described in the above JOURNAL OF APPLIED PHYSICS VOL. 52,2471, (1981). When the thickness of the NiFe alloy film is changed, the characteristics of the magnetic head itself are changed. Thus, it is not preferable to arbitrarily change the thickness of the NiFe alloy film. When the thickness of the FeMn alloy film is increased, an α-FeMn alloy phase is formed in the film, which is similarly non-preferable. In this manner, it is actually very difficult to change the exchange-coupling energy in accordance with the specifications of the magnetic head. Furthermore, as is pointed out in JOURNAL OF APPLIED PHYSICS VOL. 53,2005, (1982), the exchange-coupling energy between the FeMn alloy and the NiFe alloy largely depends on the temperature, and the characteristics of the magnetoresistance effect element may be undesirably changed by the environmental conditions and heat generation by the sense current. In order to avoid these drawbacks, IEEE TRANS. MAG-24, 2609 (1988) discloses a method of exchange-coupling a TbCo alloy with an NiFe alloy. However, since the TbCo alloy is easily oxidized, long-term reliability is not guaranteed even if the environmental conditions where the alloy is to be used are limited. The method of applying the longitudinal bias by the ferromagnetic body with a magnetization in one direction is effective if the magnetoresistance effect film is formed to be spaced apart from the magnetic recording medium, as in the yoke type magnetoresistance effect head. However, if the magnetoresistance effect film is formed close to the magnetic recording medium, as in the sealed type magnetoresistance effect head, the magnetic recording medium may undesirably be demagnetized by the leakage magnetic field from the ferromagnetic body. When the coercive force of the ferromagnetic member is decreased to avoid demagnetization, the direction of magnetization of the ferromagnetic body may undesirably be changed by the leakage magnetic field of the magnetic recording medium. In this manner, the conventional methods of applying the longitudinal bias have various drawbacks when they are applied to a magnetic recording system in which a magnetoresistance effect film and a magnetic recording medium are adjacent to each other, as in a case wherein the magnetoresistance effect head for hard disk drive is used. The document EP-A-0 406 060 discloses a magnetoresistance effect element comprising a multilayer of stached magnetic and non magnetic layers and a bias layer formed in contact with said multilayer. This bias layer can, for example, be made of Fe. It is an object of the present invention to provide a magnetoresistance effect element having a weak saturation field and capable of obtaining a high magnetoresistance ratio with a weak magnetic field. It is another object of the present invention to provide a magnetoresistance effect element capable of obtaining a high magnetoresistance ratio and decreasing the noise by suppressing generation of magnetic walls when the magnetoresistance effect element is applied to a magnetic sensor, e.g., a magnetic head. According to the present invention, there is provided a magnetoresistance effect element according to claim 1. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a graph showing the relationship between the thickness of the nonmagnetic layer and the magnetoresistance ratio; Fig. 2 is a graph showing the relationship between the thickness of the nonmagnetic layer and the saturation field; Figs. 3 to 6 are sectional views showing magnetoresistance effect elements according to the present invention; Fig. 7 shows a film forming apparatus used in the present invention; Fig. 8 is a graph showing the relationship between the external magnetic fields and the magnetoresistance ratios of Example 1 together with that of Comparative Example 1; Fig. 9 is a graph showing the relationship between the thicknesses of the Supermalloy layers of Example 2 and the magnetoresistance ratio, and relationship between the thickness and the saturation fields; Fig. 10 is a graph showing the relationship between the external magnetic field and the magnetoresistance ratio of sample No. 23 of Example 3 and Comparative Example 3; Fig. 11 is a graph showing the relationship between the external magnetic field and the magnetoresistance ratio of sample No. 25 of Example 4 and Comparative exampele 4; Fig. 12 is a graph showing the relationship Fig. is a graph showing the relationship between the thickness of the Permalloy layer as a reversal assist layer and the saturation fields, and relationship between the thickness and the magnetoresistance ratio; The preferred embodiments of the present invention will be described with reference to the accompanying drawings. According to the present invention, there is provided a magnetoresistance effect element comprising: a multilayer obtained by stacking magnetic and nonmagnetic layers to exhibit a magnetoresistance effect; and a reversal assist layer, formed in contact with said multilayer, wherein the reversal assist layer has a smaller coercive force than that of said magnetic layers to assist reversal of the direction of magnetic moment of said magnetic layers. The present inventors have made extensive studies on a magnetoresistance effect element with which a high magnetoresistance ratio can be obtained with a weak magnetic field, and have found the fact that a saturation field can be decreased, while maintaining a sufficiently high magnetoresistance ratio, by forming, on a multilayer obtained by stacking magnetic and nonmagnetic layers to exhibit a magnetoresistance effect, a reversal assist layer for assisting reversal of the magnetic moment of the magnetic layer. That is, since the magnetic moment of the magnetic layer constituting the multilayer becomes to be reversed easily due to the presence of the reversal assist layer, the magnetic moment of the magnetic layer can be reversed with a weak magnetic field while maintaining the high magnetoresistance ratio by the multilayer. Hence, a high sensitivity can be obtained. This embodiment is based on these findings of the present inventors. The magnetic layer constituting the multilayer is formed of, e.g., a transition metal such as Fe, Co, or Ni, or alloys containing at least one of such transition metals. More specifically, Fe x Co 1-x , Ni x Fe 1-x , Ni x Co 1-x or Ni x (Fe y Co 1-y ) 1-x alloys are preferable. It is preferable that two magnetic layers that are adjacent each other with one of the nonmagnetic layers interposed therebetween are antiferromagnetically coupled to each other while no magnetic field is substantially applied. Antiferromagnetic coupling means that two magnetic layers that are adjacent each other with one of nonmagnetic layers interposed therebetween are coupled to each other such that their magnetic moments are in the opposite directions. with this coupling, the magnetoresistance ratio can be increased. When the antiferromagnetic coupling force is small, the saturation field H S can be diminished, and the resultant magnetoresistance effect element is suitable as an application including a magnetic head. The thickness of the magnetic layer is preferably 0.1 nm to 10 nm. If the thickness of the magnetic layer falls outside this range, the magnetoresistance ratio tends to be decreased. A further preferable film thickness is 0.5 nm to 7 nm. The film thicknesses and compositions of the respective magnetic layers need not be the same. The material of the nonmagnetic layer is not particularly restricted as far as it is nonmagnetic and it exhibits a good magnetoresistance effect. For example, a metal such as Cr, Ru, Cu, ad, Ag, or Au, or an alloy containing such a metal can be used. The film thickness of the nonmagnetic layer is preferably 0.5 nm to 10 nm. If the film thickness of the nonmagnetic layer falls outside this range, the magnetoresistance ratio is decreased. A further preferable film thickness is 0.7 nm to 7 nm. The film thicknesses and compositions of the respective nonmagnetic layers need not be the same. The thickness and the magnetoresistance ratio of the nonmagnetic layer satisfy the relation as shown in Fig. 1. Since the magnetoresistance ratio oscillates with respect to the thickness of the nonmagnetic layer, it is preferable that the thickness of the nonmagnetic layer is determined within the range described above to obtain a high magnetoresistance ratio. As shown in Fig. 2, the saturation field also oscillates with respect to the thickness of the nonmagnetic layer, and the peak position of the saturation field overlaps the peak position of the magnetoresistance ratio. Accordingly, it is preferable that the thickness of the nonmagnetic layer is determined to balance the magnetoresistance ratio and the saturation field in accordance with the applications. Note that Figs. 1 and 2 are graphs obtained at room temperature by measuring a multilayer obtained by stacking 16 pairs of magnetic and nonmagnetic layers by using an Fe 0.1 Co 0.9 layer having a thickness of 1 nm as each magnetic layer and a Cu layer having a thickness of 1 nm as each nonmagnetic layer. The multilayer is formed by stacking these magnetic and nonmagnetic layers. The reversal assist layers have a function of assisting reversal of the magnetic moment of the magnetic layers constituting the multilayer. In order to exhibit this function, the reversal assist layer is formed of a magnetic material having a softer magnetism than that of the multilayer. The reversal assist layer exhibits above function when it is formed of a magnetic material having a softer magnetism than that of the magnetic layer having the hardest magnetism. To have the soft magnetism means that the direction of the magnetic moment can be easily reversed, and the soft magnetism can be represented by, e.g., a coercive force (Hc). That is, the smaller the Hc, the softer the magnetism. It is assumed that when the reversal assist layer is formed of such a soft magnetic material that can be easily reversed, the magnetic moment in the magnetic layer is easily reversed by the mutual function of the reversal assist layer and the magnetic layer. Examples of the material constituting the reversal assist layer are a transition metal such as Fe, Co, or Ni, and an alloy containing such a transition metal, and a material exhibiting a soft magnetism, e.g., a conventional soft magnetic material such as Permally, Supermalloy, or Sendust is preferable. The film thickness of the reversal assist layer is preferably about 0.5 nm to 100 nm, and more preferably 0.5 nm to 20 nm. Occasionally, a reversal assist layer preferably has a high electric resistance. Then, a large quantity of current can be supplied to the multilayer having the magnetoresistance effect. The multilayer and the reversal assist layer having the magnetoresistance effect as described above are generally supported on a substrate. In this case, the material of the substrate is not particularly limited. Examples of the material constituting the substrate are MgO, Cr, GdAs, Si, Cu, Fe, Co, Ni, LiF, and CaF 2 . In this embodiment, reversal assist layers are stacked on a multilayer basically having the above-described magnetoresistance effect to form an element. At this time, the number of multilayers may be one or more. A multilayer or multilayers may be formed after a reversal assist layer or layers are formed. Furthermore, reversal assist layers may be formed between a plurality of multilayers, or between every two adjacent magnetic layers. The reversal assist layer can be disposed on an outerend portion of the multilayer and can contact to the magnetic layer of the multilayer. Also, the reversal assist layer can be interposed between the substrate and the multilayer, and can contact to the nonmagnetic layer of the multilayer. The number of reversal assist layers may be one or more. For example, a plurality of reversal assist layers may be stacked with nonmagnetic layers interposed therebetween, and a multilayer having the above magnetoresistance effect may be stacked on the reversal assist layers. At least one of the reversal assist layers can be interposed between two of the magnetic layers, the magnetic layer and the nonmagnetic layer, or two of the nonmagnetic layers of the multilayer. For example, when a state wherein m or n (m ≠ n) magnetic layers M each having a film thickness tM and m or n nonmagnetic layers N each having a film thickness tN are alternately stacked to form a multilayer is represented as (tMM/tNN) n , (tNN/tMM) n , (tMM/tNN) m , or (tNN/tMM) m , a state wherein ℓ (ℓ is an integer more than 1) multilayers and ℓ reversal assist layers M' each having a film thickness of tM' are alternately stacked is represented as [tM'M'/(tMM/tNN) n ] ℓ , [tM'M/tNN/(tMM/tNN) n ] ℓ , [(tMM/tNN) n /tM'M'] ℓ , [(tMM/tNN) n /tMM/tM'M'] ℓ , [tM'M/(tNN/tMM) n ] ℓ , [tM'M/(tNN/tMM/tMM) n ] ℓ , [(tNN/tMM) n /tM'M] ℓ , or [(tNN/tMM) n /tNN/tM'M] ℓ , [(tNN/tMM) m /tM'M/(tNN/tMM) n ] ℓ . Any of the cases described above, it is preferable that the reversal assist layer or layers made of the soft magnetic material and one or two magnetic layers in the multilayer contact each other. The practical structure of the magnetoresistance effect element of this embodiment will be described. Fig. 3 shows an arrangement in which a multilayer 4 obtained by alternately stacking magnetic and nonmagnetic layers 2 and 3 is formed on a substrate 1, and a reversal assist layer 5 is formed on the multilayer 4. Fig. 4 shows an arrangement in which a reversal inversion assist layer 5 is formed on a substrate 1, and a multilayer 4 is formed on the reversal assist layer 5. Fig. 5 shows an arrangement having a plurality of multilayers 4, in which reversal assist layers 5 are present between the respective multilayers 4. Fig. 6 shows an arrangement in which a plurality of inversion assist layers 5 are stacked on a substrate 1 with nonmagnetic layers 6 interposed therebetween, and a multilayer 4 is formed on the uppermost inversion assist layer 5. A magnetoresistance effect element having an arrangement as described above is formed in accordance with an ordinary thin film forming method, e.g., vapor deposition, sputtering, or molecular beam epitaxy (MBE). Film formation or annealing may be performed in a magnetic field to decrease the saturation field. Fig. 7 shows an ion beam sputtering system as an example of a film forming system. An exhaust port 12 of a chamber 11 is connected to a vacuum pump (not shown), and the pressure in the chamber 11 is measured by a pressure gauge 13. A substrate holder 14 is placed in the chamber 11, and a substrate 15 is held by the substrate holder 14. A heater 16 is provided to the substrate holder 14. Cooling water 17 flows near the substrate holder 14 to adjust the temperature of the substrate holder 14 and the substrate 15. The temperature of the substrate holder 14 is measured by a thermocouple 18. A shutter 19 is provided in front of the substrate 15. A target holder 20 is rotatably provided at a position opposing the substrate 15, and a plurality of targets 21 are mounted on the surface of the target holder 20. The target holder 20 is cooled by cooling water 22. An ion gun 23 is provided at a position opposing the targets 21, and Ar gas 24 is supplied to the ion gun 23. With this arrangement, ions from the ion gun 23 are projected toward the targets 21. Then, the targets 21 are sputtered and the elements constituting the targets 21 are deposited on the substrate 15. EXAMPLES Examples of the present invention will be described. Example 1 Using the ion beam sputtering system shown in Fig. 7 described above, magnetoresistance effect elements as shown in Table 1 were fabricated in accordance with the following procedures. The interior of the chamber 11 was evacuated to a vacuum degree of 5.33 . 10 -5 pa (4x10 -7 ), Ar gas 24 (purity: 99.99%) was supplied to the ion gun 23 until the partial pressure reached 0.02pa (1.5x10 -4 Torr), and Ar was ionized and radiated to targets 21 as an ion beam having an acceleration voltage of 700 V and a beam current of 30 mA. The targets 21 included three types, i.e., a target made of Co as a magnetic metal to constitute the magnetic layer of the multilayer that exhibited the magnetoresistance effect, a target made of Cu as a nonmagnetic metal to constitute the nonmagnetic layer, and a target made of an 80 wt% Ni 20 wt% Fe alloy (to be referred to as Permalloy hereinafter) as a magnetic metal to constitute the reversal assist magnetic layer. The target holder 20 was switchingly rotated every predetermined period of time. The film thickness of Co and Cu was set as shown in Table 1, the number of repetition times of the Co and Cu layers was set to 60, and the film thickness of the Permalloy layer was changed in the range of 2.5 nm to 50 nm. Single-crystal MgO (110) was used as the material of the substrate 15, and the substrate temperature was set to room temperature. In addition to sample Nos. 1 to 10, a sample of Comparative Example 1 in which a Permalloy layer as the reversal assist layer was not formed was fabricated in this manner. The magnetoresistance effects of the magnetoresistance effect elements fabricated in the above manner with respect to the external magnetic field were measured in accordance with the ordinary four point method. Fig. 8 shows the relationship between the external magnetic field (H) and the magnetoresistance ratio (ΔR/Rs) of Comparative Example 1 and sample No. 2. It is seen from Fig. 8 that, in Comparative Example 1 wherein no reversal assist layer is formed, the magnetoresistance ratio (ΔR/Rs) is 35% and the saturation field (H S ) is 6 kOe, whereas in sample No. 2, although the magnetoresistance ratio (ΔR/Rs) is 35% without any change, the saturation field (H S ) is largely decreased to 1 kOe. In this manner, it was confirmed that the magnetoresistance effect element exhibited a better magnetoresistance effect by providing a reversal assist layer. The same measurements as that described above were conducted for the samples of other examples, and results similar to that of sample No. 2 were obtained. Furthermore, samples were fabricated by changing the materials constituting the magnetic and nonmagnetic layers of the multilayers and their thicknesses, and their magnetoresistance effects and saturation fields were measured. Similar effects to that of sample No. 2 were obtained. Example 2 Using a 79 wt% Ni 16 wt% Fe 5 wt% Mo alloy (to be referred to as the Supermalloy hereinafter) as the soft magnetic material to constitute the reversal assist layer, using a 1-nm thick Co 0.9 Fe 0.1 alloy (to be referred to as the Co9Fe hereinafter) as the magnetic layer of the multilayer having the magnetoresistance effect, using a 1.1-nm thick Cu film as the nonmagnetic layer, setting the number of repetition times of the Co9Fe alloy layer and the Cu layer to 60, and using single-crystal MgO (110) as the material of the substrate, magnetoresistance effect elements having the film structures as shown in Table 2 were fabricated in accordance with the same method as in Example 1. In addition to sample Nos. 10 to 18, a sample of Comparative Example 2 in which a Permalloy layer as the reversal assist layer was not formed was fabricated in this manner. The influences of the magnetoresistance ratio (ΔR/Rs) of the magnetoresistance effect elements fabricated in this manner with respect to the external magnetic field (H) were measured. Fig. 9 shows the relationship between the thickness of the Supermalloy layers of sample Nos. 10 to 11 and the magnetoresistance ratio, and the relationship between the thickness and the saturation field. It can be seen from Fig. 9 that the magnetoresistance ratio is 40% and the saturation field is 4 kOe when no Supermalloy layer is provided, whereas the magnetoresistance ratio becomes 47% and the saturation field becomes 2 kOe only by providing a 2.5-nm thick Supermalloy layer. Also, when the film thickness is increased, although the magnetoresistance ratio is gradually decreased, the saturation field is greatly decreased. In this manner, it was confirmed that a high magnetoresistance ratio was obtained with a weak magnetic field by providing a reversal assist layer made of a soft magnetic material. Similar effects were obtained for other samples measured in a similar manner. Furthermore, as the soft magnetic layer constituting the reversal assist layer, samples using various materials, e.g., 85 at% Fe 5 at% Aℓ 10 at% Si (Sendust), 45 at% Ni 25 at% Co 30 at% Fe (Permendur), 90 at% Co 10 at% Zr, or the like were fabricated. Their magnetoresistance effects were measured, and similar effects to that described above were obtained. Example 3 Using two 5-nm thick Ni 0.8 Fe 0.2 films, with a 1-nm thick Cu layer interposed therebetween, as the soft magnetic layers serving as the reversal assist layers, using a 0.7-nm thick Fe 0.25 Co 0.75 alloy as the magnetic layer and a 1-nm thick Cu film as the nonmagnetic layer, respectively, of the multilayer having the magnetoresistance effect, using single-crystal MgO (110) as the material of the substrate, and providing an Fe buffer layer between the substrate and the multilayer, magnetoresistance effect elements having the film structures as shown in Table 3 were fabricated in accordance with the same method as in Example 1. In addition to sample No. 19 of Example 3, a sample of Comparative Example 3 in which a reversal assist layer was not formed was fabricated. The influences of the magnetoresistance ratios of the magnetoresistance effect elements fabricated in this manner on the external magnetic field was evaluated in the same manner as in Example 1. Fig. 10 shows the relationship between the external magnetic field and the magnetoresistance ratios of sample No. 19 of Example 3 and Comparative Example 3. Referring to Fig. 10, reference symbol a denotes sample No. 23; and b, Comparative Example 3. It can be seen from Fig. 32 that the saturation fields (H s ) are respectively 3 kOe and 6.5 kOe indicating that the saturation field of Comparative Example 3 is large, whereas the both magnetoresistance ratios are 25% indicating substantially no change. In this manner, it was confirmed that the saturation field could be decreased while maintaining a high magnetoresistance ratio by providing a reversal assist layer. Example 4 Using a 2.5 nm thickness Permalloy film as the soft magnetic material to scene as the reversal assist layer, using a 1 nm thickness C0.9Fe alloy as the magnetic layer of the multilayer having the magnetoresistance effect, using 1 nm thick Cu film as the nonmagnetic layer, setting the number of repetition times of the magnetic and nonmagnetic layers to 60, using single-crystal MgO (110) as the material of the substrate, magnetoresistance effect element having the film structures as shown in Table 4 were fabricated in accordance with the same method as in Example 1. In addition to sample No. 20 as the sample of Example 4, in which a Permalloy layer as the reversal assist layer was not formed was fabricated. The relationship between the external magnetic field and the magnetoresistance ratio of the magnetoresistance effect elements fabricated in this manner was evaluated in the same manner as in Example 1. Fig. 11 shows the relationship between the external magnetic field and the magnetoresistance ratio of the sample No. and Comparative Example 4. In Fig. 11 reference symbol a denotes sample No. 25; and b , Comparative Example 4 . It can be seen from Fig. that the saturation fields (H s ) are respectively 2.4 kOe and 3.7 kOe indicating that the saturation field of Comparative Example 4 is large, whereas the magnetoresistance ratios are the same each other. In this manner, it was confirmed that the satrucation field could be decreased while maintaining a high magnetoresistance ratio by providing a reversal assist layer. Next, changing the thickness of the Permalloy layer, the influence of the magnetoresistance ratio (ΔR/Rs) of the magnetoresistance effect elements fabricated in this manner with expect to the external magnetic field (H) were measured. Fig. 12 shows the relationship between the thickness of the Permalloy layers and the saturation field, and the relationship between the thickness and the magnetoresistance ratio. It can be seen from Fig. 12 that the saturation field 3.2 KOe when no Permalloy layer is provide, whereas the saturation field decreases 2 KOe by providing 2.5 mm thick Permalloy Layer. ΔR/Rs value is maintained 47 to 50% even if the thickness of the Permalloy layer changes. In this manner, it was confirmed that a low saturation field was obtained maintaining a high magnetoresistance ratio by providing a reversal assist layer of a soft magnetic material having suitable thickness.

Claims: A magnetoresistance effect element comprising: a multilayer (4) obtained by stacking magnetic and nonmagnetic layers (2 and 3) to exhibit a magnetoresistance effect; and a reversal assist layer (5), formed in contact with said multilayer (4), wherein the reversal assist layer (5) has a smaller coercive force than that of said magnetic layers (2) to assist reversal of the direction of magnetic moment of said magnetic layers (2). An element according to claim 1, wherein the reversal assist layer (5) is formed in contact with the magnetic layer (2) of the multilayer (4). An element according to claim 1, wherein the reversal assist layer (5) has a film thickness larger than that of said magnetic layers (2) of said multilayer (4). An element according to claim 1, wherein the magnetic layers (2) of said multilayer (4) contains Fe, Co, Ni, or an alloy containing Fe, Co, or Ni. An element according to claim 1, wherein the nonmagnetic layers (3) of said multilayer (4) contain Cr, Ru, Cu, Aℓ, Ag, Au, or an alloy containing Cr, Ru, Cu, Aℓ, Ag, or Au. An element according to claim 1, wherein the magnetic layers (2) of said multilayer (4) have a film thickness of 0.1 nm to 10 nm. An element according to claim 1, wherein the nonmagnetic layers (3) of said multilayer (4) have a film thickness of 0.5 nm to 10 nm. An element according to claim 1, wherein the reversal assist layer (5) is disposed on an outer end portion of said multilayer (4) and contacts to said magnetic layer (2) of said multilayer (4). An element according to claim 1, wherein the reversal assist layer (5) is interposed between a substrate (1) and said multilayer (4), and contacts to said nonmagnetic layer (3) of said multilayer (4). An element according to claim 1, further comprising another reversal assist layer (5) and/or another multilayer (4). An element according to claim 1, wherein at least one of said reversal assist layers (5) is interposed between two of said magnetic layers (2), said magnetic layer (2) and said nonmagnetic layer (3), or two of said nonmagnetic layers (3) of said multilayer (4).

Inventors: AKIYAMA JUNICHI, HASHIMOTO SUSUMU, INOMATA KOICHIRO, IWASAKI HITOSHI, KONDOH REIKO, OHSAWA YUICHI, OHTA TOSHIHIKO, SAITO YOSHIAKI, AKIYAMA, JUNICHI, HASHIMOTO, SUSUMU, INOMATA, KOICHIRO, IWASAKI, HITOSHI, KONDOH, REIKO, OHSAWA, YUICHI, OHTA, TOSHIHIKO, SAITO, YOSHIAKI, AKIYAMA, JUNICHI,C/O INT.PROP.DIV., K.K. TOSHIBA, Hashimoto, Susumu, c/o Int.Prop.Div., K.K. Toshiba, Inomata, Koichiro, c/o Int.Prop.Div., K.K. Toshiba, Iwasaki, Hitoshi, c/o Int.Prop.Div., K.K. Toshiba, Kondoh, Reiko, c/o Int.Prop.Div., K.K. Toshiba, OHSAWA, YUICHI,C/O INT.PROP.DIV., K.K. TOSHIBA, OHTA, TOSHIHIKO,C/O INT.PROP.DIV., K.K. TOSHIBA, Saito, Yoshiaki, c/o Int.Prop.Div., K.K. Toshiba
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1992
Main classification: H01L43
IPC codes: H01L43, G01R33, G11B5