Patent Publication Number: US-7898774-B2

Title: Magnetoresistive effect element with resistance adjustment layer of semimetal, magnetic head and magnetic reproducing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present divisional application claims the benefit of priority under 35 U.S.C. §120 to application Ser. No. 11/282,659, filed on Nov. 21, 2005, and application Ser. No. 10/175,960, filed Jun. 21, 2002, and under 35 U.S.C. §119 from Japanese Patent Application No. 2001-190511, filed Jun. 22, 2001, the entire contents of each are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a magnetoresistive effect element, magnetic head and magnetic recording apparatus, and more particularly, to a magnetoresistive effect element structured to flow a sense current perpendicularly of the film surface of a magnetoresistive effect film, as well as a magnetic head and a magnetic reproducing apparatus using the magnetoresistive effect element. 
     Read-out of information recorded in a magnetic recording medium conventionally relied on a method of moving a reproducing magnetic head having a coil relative to the recording medium and detecting a current induced in the coil by electromagnetic induction then generated. Later, a magnetoresistive effect element was developed, and has been brought into practical use as a magnetic field sensor as well as a magnetic head (MR head) incorporated in a magnetic reproducing apparatus such as a hard disk drive. 
     For years, magnetic recording mediums have been progressively downsized and enhanced in capacity, and the relative speed between the reproducing magnetic head and the magnetic recording medium during information read-out operation has been decreased accordingly. Under the circumstances, there is the increasing expectation for MR heads capable of extracting large outputs even with small relative speeds. 
     As an answer to the expectation, it has been reported that multi-layered films, so called an “artificial lattice films”, which are made by alternately depositing ferromagnetic metal films and nonmagnetic metal films, such as the combination of Fe layers and Cr layers or the combination of Fe layers and Cu layers, under certain conditions, and bringing closely located ferromagnetic metal films into antiferromagnetic coupling, exhibit giant magnetoresistive effects (see Phys. Rev. Lett. 61 2474 (1988), Phys. Rev. Lett., vol. 64, p 2304 (1990), for example). Artificial films, however, need a large magnetic field for magnetic saturation, and are not suitable as film materials for MR heads. 
     On the other hand, there are reports about realization of a large magnetoresistive effect by using a multi-layered film of the sandwich structure of a ferromagnetic layer on a nonmagnetic layer and a ferromagnetic layer even when the ferromagnetic layer is not under ferromagnetic coupling. According to this report, one of two layers sandwiching the nonmagnetic layer is fixed in magnetization beforehand by application of an exchanging bias magnetic field thereto, and the other ferromagnetic layer is magnetically reversed with an external magnetic field (signal magnetic field, for example). It results in changing the relative angle between the magnetization directions of these two ferromagnetic layers on opposite surfaces of the nonmagnetic layer, and exerting a large magnetoresistive effect. The multi-layered structure of this kind is often called “spin valve” (see Phys. Rev. B, vol. 45, p 806 (1992), J. Appl. Phys., vol. 69, p 4774) (1981) and others). 
     Spin valves that can be magnetically saturated under a low magnetic field are suitable as MR heads and are already brought into practical use. However, their magnetoresistive variable rates are only 20% maximum. Therefore, to cope with area recording densities not lower than 100 Gbpsi (gigabit per square inch), there is the need of a magnetoresistive effect element having a higher magnetoresistance variable rate. 
     As its substitutional technique, a TMR (tunneling magnetoresistance) element has been proposed. The TMR element makes use of the phenomenon that spin-polarized electrons tunnel through an insulating barrier layer, and it exhibits an excellent magnetoresistance variable rate as high as 50% or more. However, to satisfy the magnetoresistance variable rate as high as 30%, for example, the area resistivity of the element becomes as high as 100 Ωμm 2 . Since reproducing heads for handling area recording densities not lower than 100 Gbpsi need downsizing the device area to a level not smaller than 0.1 μm 2 , resistance of the TMR element increases to kΩ or higher, and results in decreasing S/N. To the contrary, if the resistance is lowered to about 10 Ωm 2 , then the magnetoresistance variable rate also decreases to about 10%. Therefore, there is no clear prospect toward its practical use. 
     Structures of magnetoresistive effect elements are classified into CIP. (current-in-plane) type structures permitting a sense current to flow in parallel to the film plane of the element and CPP (current-perpendicular-to-plane) type structures permitting a sense current to flow perpendicularly to the film plane of the element. Considering that CPP type magnetoresistive effect elements were reported to exhibit magnetoresistance variable rates as large as approximately ten times those of CIP type elements (J. Phys. Condens. Mater., vol. 11, p. 5717 (1999) and others), realization of the magnetoresistance variable rate of 100% is not impossible. 
     However, CPP type elements having been heretofore reported mainly use artificial lattices, and a large total thickness of films and a large number of boundary faces caused a large variation of resistance (output absolute value). To realize a satisfactory magnetic property required for a head, the use of a spin valve structure is desirable. 
       FIG. 16  is a cross-sectional view that schematically showing a CPP type magnetoresistive effect element having a spin valve structure. A magnetoresistive effect film M is interposed between an upper electrode  52  and a lower electrode  54 , and a sense current flows perpendicularly to the film plane. The magnetoresistive effect film M shown here has the basic film structure sequentially made by depositing a base layer  12 , antiferromagnetic layer  14 , magnetization-fixed layer  16 , nonmagnetic intermediate layer  18 , magnetization free layer  20  and protective layer  22  on the lower electrode  54 . 
     As these layers are made of metals. The magnetization-fixed layer (called pinned layer) is a magnetic layer in which magnetization is fixed substantially in one direction. The magnetization free layer  20  (called free layer) is a magnetic layer in which the direction of magnetization can freely change depending upon an external magnetic field. 
     This kind of spin valve structure, however, has a smaller total thickness and fewer boundary faces than those of artificial lattices. Therefore, if a current is supplied perpendicularly to the film plane, then the area resistivity AR becomes as small as the order of tens of mΩμm 2 . Of this resistance, the resistance of the active portion in charge of changes of the magnetoresistance is approximately 1 through 2 mΩμm 2 . As a result, even if the magnetoresistance variable rate is 50%, the area resistivity variable rate AΔR obtained is as small as 0.5 mΩμm 2 , approximately. 
     BRIEF SUMMARY OF THE INVENTION 
     According to an embodiment of the invention, there is provided a magnetoresistive effect element comprising: a magnetoresistive effect film including a magnetization-pinned layer having a magnetic film whose direction of magnetization is pinned substantially in one direction, a magnetization free layer having a magnetic film whose direction of magnetization varies in response to an external magnetic field, a nonmagnetic metallic intermediate layer interposed between the magnetization-pinned layer and the magnetization free layer, and a resistance adjustment layer interposed between the magnetization-pinned layer and the magnetization free layer and made of a material containing a quantity of conductive carriers not more than 10 22 /cm 3 ; and a pair of electrodes electrically coupled to the magnetoresistive effect film to supply a sense current substantially vertically of the film plane of the magnetoresistive effect film. 
     According to another embodiment of the invention, there is provided a magnetoresistive effect element comprising: a magnetoresistive effect film including a magnetization-pinned layer having a magnetic film whose direction of magnetization is pinned substantially in one direction, a magnetization free layer having a magnetic film whose direction of magnetization varies in response to an external magnetic field, and a nonmagnetic metallic intermediate layer interposed between said magnetization-pinned layer and said magnetization free layer; a pair of electrodes electrically coupled to said magnetoresistive effect film to supply a sense current substantially vertically of the film plane of said magnetoresistive effect film, wherein said nonmagnetic intermediate layer is a resistance adjustment layer made of a material containing conductive carriers not more than 10 22 /cm 3 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the embodiments of the invention. However, the drawings are not intended to imply limitation of the invention to a specific embodiment, but are for explanation and understanding only. 
       In the drawings: 
         FIG. 1  is a schematic diagram that shows a cross-sectional structure of the substantially part of a magnetoresistive effect element according to the first embodiment of the invention; 
         FIG. 2  is a schematic diagram that shows a cross-sectional structure of a magnetoresistive effect element having a synthetic type pinned layer; 
         FIG. 3  is a schematic diagram that shows a modification of the first embodiment; 
         FIG. 4  is a schematic diagram that shows a cross-sectional structure of the substantial part of a magnetoresistive effect element according to the second embodiment of the invention; 
         FIG. 5  is a schematic diagram that shows a modification of the second embodiment; 
         FIG. 6  is a schematic diagram that shows a cross-sectional structure of the substantial part of a magnetoresistive effect element according to the third embodiment of the invention; 
         FIG. 7  is a schematic diagram that shows a modification of the third embodiment; 
         FIG. 8  is a schematic diagram that shows a cross-sectional structure of a magnetoresistive effect element in which a magnetization-free layer  20  is located lower in an embodiment of the invention; 
         FIG. 9  is a schematic diagram that shows a cross-sectional structure of a magnetoresistive effect element in which a magnetization-free layer  20  is located lower in an embodiment of the invention; 
         FIG. 10  is a schematic diagram that shows a modification of the synthetic type magnetoresistive effect element of  FIG. 2 ; 
         FIG. 11  is a schematic diagram that shows a cross-sectional structure of a magnetoresistive effect element employing a multi-layered structure; 
         FIG. 12  is a schematic diagram that shows a cross-sectional structure of a magnetoresistive effect element including an oxide layer  60  between the free layer  20  and a protective layer  22 ; 
         FIG. 13  is a schematic diagram that shows a cross-sectional structure of a magnetoresistive effect element having the oxide film  60  inserted in a pinned layer  16 ; 
         FIG. 14  is a perspective view that shows outline configuration of this kind of magnetic recording apparatus; 
         FIG. 15  is a perspective view of a magnetic head assembly at the distal end from an actuator arm  155  involved, which is viewed from the disk; and 
         FIG. 16  is a cross-sectional view that schematically shows a CPP type magnetoresistive effect element having a spin valve structure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Some embodiments of the invention will now be explained below with reference to the drawings. 
     First Embodiment 
     Explanation is started with the first embodiment of the invention which is a configuration including a resistance adjustment layer made of a semiconductor or a semimetal. 
       FIG. 1  is a schematic diagram that shows a cross-sectional structure of the substantially part of a magnetoresistive effect element according to the first embodiment. More specifically, the magnetoresistive effect element according to the embodiment has a structure made by sequentially depositing a base layer  12 , resistance adjustment layer  30 , nonmagnetic intermediate layer  18 , free layer  20 , protective layer  22  and upper electrode  52  on a lower electrode  54 . 
     In the illustrated magnetoresistive effect element, it is the portion of the pinned layer  16 , nonmagnetic intermediate layer  18  and free layer  20  that takes charge of the magnetoresistive effect. That is, in this portion, a resistance depending upon spins is generated against spin-polarized electrons. That is, a spin-relied resistance is generated. In order to fabricate a magnetoresistive effect element enhanced in device output, i.e. absolute value of the magnetoresistance variable amount, to a degree acceptable for practical use, it is effective to increase the resistance value of the portion having the spin-relied resistance. 
     To obtain a large output in a CPP type spin valve structure, it is important to adequately improve the resistance of the portion in charge of spin-relied conduction and thereby increase the resistance variable amount. In this case, from the viewpoint of S/N and heat evolution issues, resistance of the magnetoresistive effect element is preferably around hundreds of mΩμm 2 . 
     Taking it into consideration, in the instant embodiment of the invention, the resistance adjustment layer  30 , in which the concentration of electrons or other carriers for conduction is inherently lower than those of metals, namely, not higher than approximately 10 22  cm −3 , is inserted in the portion in charge of the magnetoresistance, and the resistance is increased adequately. 
     Preferable materials of this kind of resistance adjustment layer  30  are semiconductors or semimetals. Unlike the insulating barrier layer of a TMR element, the resistance adjustment layer  30  used in the embodiment of the invention and made of such a material contain conduction carriers, and can therefore overcome the problem of an excessive increase of the device resistivity by adjusting the thickness of the film. 
     In case spin-polarized electrons are injected into a nonmagnetic material (metal, semimetal, semiconductor), since the spins do not relax and remain conductive within the spin diffusion length, it is effective for increasing the magnetoresistance variable amount. 
     That is, the embodiment of the invention can appropriately increase the resistance of the magnetoresistive effect element and can enhance its output. 
     Respective components forming the magnetoresistive effect element according to the embodiment of the invention will be explained below. 
     The base layer  12  is preferably made of a material having the function of improving the crystal properties of the overlying free layer  20  and the pinned layer  16  as well as the function of smoothing boundaries. For example, Ni—Fe—Cr alloy containing Cr by approximately 40% is one of such materials. For the purpose of ensuring better orientation, a layer (not shown) of NiFe, Ru or Cu, for example, may be inserted between the base layer  12  and the antiferromagnetic layer  14 . 
     The antiferromagnetic layer  14  functions to fix magnetization of the pinned layer  16 . That is, by locating the antiferromagnetic layer  14  made of PtMn, IrMn, PdPtMn, NiMn, or the like, adjacent to the pinned layer  16 , magnetization of the pinned layer  16  can be fixed in one direction by making use of the exchanging coupling bias magnetic field generated along the interface. 
     To enhance the effect of fixing magnetization of the pinned layer  16 , a magnetically coupling intermediate layer (not shown) is preferably inserted between the antiferromagnetic layer  14  and the pinned layer  16 . Ferromagnetic alloys containing Fe, Co or Ni, for example, as their major components are usable as the material of the magnetically coupling intermediate layer. Its thickness must be very thin, namely, as thin as 0.1 through 3 nm, for restricting magnetization of the pinned layer  16 . 
     For the purpose of stabilizing the fixed magnetization, a so-called synthetic type multi-layered structure that is a ferri-type multi-layered of a ferromagnetic layer, anti-parallel coupling layer and ferromagnetic layer employed in spin-valve GMR is also preferable as the magnetically coupling intermediate layer. 
       FIG. 2  is a schematic diagram that shows a cross-sectional structure of a magnetoresistive effect element having a synthetic type pinned layer. Here are formed a first ferromagnetic layer  16 A, anti-parallel coupling layer  16 B and second ferromagnetic layer  16 C as the pinned layer  16 . The anti-parallel coupling layer  16 B has the role of coupling the upper and lower ferromagnetic layers in an anti-parallel magnetization direction, and Ru (ruthenium) can be used as its material. In the synthetic multi-layered structure, upper and lower ferromagnetic layers are brought into antiferromagnetic coupling via the anti-parallel coupling layer  16 B. 
     The resistance adjustment layer  30  has the role of appropriately increasing the resistance value of a part of the magnetoresistive effect element, which has a spin-relied resistance, as already referred to. For this purpose, the resistance adjustment layer  30  is preferably made of a material inherently having a lower concentration of electrons or other carriers in charge of conduction that those of metals, namely, not higher than approximately 10 22  cm −3 . Semiconductors or semimetals are appropriate as such materials. 
     When using semiconductor materials, such as C, Si, Ge, MN, GaN, InN, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnO, β-ZnS, ZnSe, ZnTe, CdS, CdTe, HgTe, α-SiC, β-SiC, PbS, PbSe, PbTe, SnTe, SnTe, CuInSe 2 , FeSi 2.43 , β-FeSi 2 , MnSi 1.72 , CrSe 2 , (Cr 1-x Mnx)Si 2 , Mg 2 Si, BaSi 2 , ReSi 1.75 , RuSi 3 , OSi 2 , Ir 3 Si 5 , etc., the tendency of increasing the output was observed. 
     However, semiconductors generally exhibit slightly higher specific resistance values as high as several Ωcm to kΩcm. If, for example, a 1 nm thick layer of a semiconductor having the specific resistance of 10 Ωcm is inserted, then the device resistivity AR rises to 10 Ωμm 2 , which is about a hundred times of appropriate values around hundreds of mΩμm 2 . 
     In contrast, the use of semimetals having lower resistance values is effective for decreasing the resistance. Examples of such semimetals are graphite, As, Sb, Bi, HgTe, HgSe, CoSi, (Co 1-x Fe x )Si, (Co 1-x Ni x )Si, (Co 1-x Mn x )Si, (Co 1-x Cr x )Si and FeSi. These semimetals are relatively low in specific resistance, ranging from a lower value around 40 μΩm of Sb to a higher value around 1 mΩcm. Therefore, they need not be thinned for the purpose of adjusting the device resistivity. However, from the viewpoint of preventing relaxation of spins in the layer, the thickness of such a semimetal is preferably limited not to exceed 1 nm. 
     The nonmagnetic intermediate layer  18  has the role of interrupting magnetic coupling between the pinned layer  16  and the free layer  20 . It is desirable that the nonmagnetic intermediate layer  18  also functions to improve the interface between the nonmagnetic intermediate layer  18  and the pinned layer  16  such that the up-spin electrons flowing from the pinned layer  16  to the free layer  20  are not scattered. Possible materials of the nonmagnetic intermediate layer  18  are, for example, Cu, Au, Ag, Ru, Ir, Pd, Cr, Mg, Al, Rh, Pt, and so on. The layer  18  should be thick enough to sufficiently interrupt magnetic coupling between the free layer  20  and the pinned layer  16  and thin enough to prevent scattering of the up-spin electrons from the pinned layer  16 . Namely, the thickness is preferably in the range from 0.5 to 5 nm, although depending upon its material. 
     The free layer  20  is a magnetic layer in which the direction of magnetization changes with an external signal magnetic field. Usable materials thereof are, for example, CoFe, NiFe and CoFeNi alloys. If these alloys additionally contain any of Sc, Ti, Mn, Cu, Zn, Ga, Ge, Zr, Hf, Y, Tc, Re, Ru, Rh, Ir, Pd, Pt, Ag, Au, B, Al, In, C, Si, Ca, Sr, etc., they will ensure higher outputs. 
     A multi-layered structure of these alloys is also usable. Examples of such multi-layered structures are NiFe/CoFe, CoFe/NiFe, NiFe/CoFe/NiFe, CoFe/NiFe/CoFe, and so forth. 
     Also usable as the free layer  20  is a multi-layered structure of any of those alloys and a nonmagnetic layer. Examples of such multi-layered structures are CoFe/Cu/CoFe, NiFe/CoFe/Cu/CoFe/NiFe, etc. In this case, Co-system alloys, which enhance scattering at interfaces with nonmagnetic layers, are hopeful as enhancing the effect of lamination with nonmagnetic layers than Ni-system alloys. 
     The total thickness of the free layer  20  is preferably in a range between 0.5 through 7 nm. 
     The protective layer  22  has the role of protecting the multi-layered structure of the magnetoresistive effect film during patterning and other processing. 
     The Inventors prepared magnetoresistive effect elements A 1 , A 2  and A 3  of the synthetic structure shown in  FIG. 2 , and compared them with a magnetoresistive effect element A 0  of the conventional structure shown in  FIG. 16 . 
     Materials and thicknesses of respective layers forming the prepared magnetoresistive effect elements are listed below. 
     
       
         
           
               
             
               
                   
               
               
                 &lt;Magnetoresistive effect elements A0, A1, A2, A3&gt; 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Protective layer 22 
                 Ta 
                 (5 nm) 
               
               
                   
                 Second free layer 20 
                 (Co 86 Fe 14 ) 82 Ni 18   
                 (4 nm) 
               
               
                   
                 First free layer 20 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (2 nm) 
               
               
                   
                 Nonmagnetic intermediate 
                 Cu 
                 (3 nm) 
               
               
                   
                 layer 18 
                   
                   
               
               
                   
                 Pinned layer 16C 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (3 nm) 
               
               
                   
                 Pinned layer 16B 
                 Ru 
                 (1 nm) 
               
               
                   
                 Pinned layer 16A 
                 Co 90 Fe 10   
                 (3 nm) 
               
               
                   
                 Antiferromagnetic 
                 PtMn 
                 (15 nm)  
               
               
                   
                 layer 14 
                   
                   
               
               
                   
                 Second base layer 12 
                 Ru 
                 (2 nm) 
               
               
                   
                 First base layer 12 
                 Ta 
                 (5 nm) 
               
               
                   
               
            
           
         
       
     
     The prepared magnetoresistive effect elements A 0 , A 1 , A 2  and A 3  were common in the above-indicated structure. The free layer  20  used here was a multi-layered structure of the first and second nonmagnetic layers. The pinned layer  16  was a synthetic structure stacking two kinds of ferromagnetic layers on opposite surfaces of a Ru (ruthenium) layer. The base layer  12  was formed as a two-layered structure. 
     In the magnetoresistive effect elements A 1 , A 2  and A 3  according to the embodiment of the invention, a resistance adjustment layer  30  was inserted between the pinned layer  16  and the nonmagnetic intermediate layer  18  as shown in  FIG. 2 . Material and thickness of the resistance adjustment layer  30  in each element were as follows. 
     
       
         
           
               
             
               
                   
               
             
            
               
                 &lt;Magnetoresistive effect element A1&gt; 
               
            
           
           
               
               
               
               
            
               
                   
                 Resistance adjustment layer 30 
                 GaAs 
                 (1 nm) 
               
            
           
           
               
            
               
                 &lt;Magnetoresistive effect element A2&gt; 
               
            
           
           
               
               
               
               
            
               
                   
                 Resistance adjustment layer 30 
                 CoSi 
                 (1 nm) 
               
            
           
           
               
            
               
                 &lt;Magnetoresistive effect element A3&gt; 
               
            
           
           
               
               
               
               
            
               
                   
                 Resistance adjustment layer 30 
                 (Fe 10 Co 90 ) Si 
                 (1 nm) 
               
               
                   
               
            
           
         
       
     
     For preparing those magnetoresistive effect elements, the following two kinds of process were carried out. 
     The first process of preparation is explained below. 
     AlO x  is deposited on a Si (silicon) substrate to form a 500 nm thick film, and a resist is coated thereon. A part of the resist in the region for the lower electrode is removed by PEP (photo engraving process). After that, a part of AlO x  in the region without the resist is removed by RIE (reactive ion etching), and a multi-layered structure of Ta (5 nm)/Cu (400 nm) is formed as the lower electrode  54 . 
     After that, the surface is smoothed by CMP (chemical mechanical polishing) to the surface of A 10 . not covered by the resist on the surface. Then a magnetoresistive effect film sized 3×3 μm 2  to 5×5 μm 2  is formed thereon, and a hard bias applying film made of CoPt is formed on side surfaces thereof up to the thickness of 30 nm. 
     After that, 200 nm thick SiO x  is deposited as a passivation film, and a resist is coated. Then the resist is partly removed from the region for making a contact hole in a central area of the spin valve, and after etching by RIE, the resist is removed entirely. Thereafter, etching by ion milling is carried out for removal of carbides. After that, a multi-layered structure of Ta (5 nm)/Cu (400 nm)/Ta (5 nm) is formed as the upper electrode  52 , and an electrode pad of 200 nm thick Au (gold) is formed, thereby to complete the substantial part of the magnetoresistive effect element. 
     The second process of preparation is next explained below. 
     First formed on a thermal oxide Si substrate is the lower electrode  54  (Ta 5 nm/Cu 300 nm/Ta (20 nm) by using a metal mask. Still using the metal mask, a magnetoresistive effect film is formed thereon. When PtMn is used as the antiferromagnetic layer  14 , the structure is annealed in a magnetic field at 270° C. for 10 hours, thereby to fix the magnetization of the pinned layer  16 . Area of the magnetoresistive effect film is determined as large as approximately 2 mmΦ, taking the magnetic property into consideration. 
     After that, SiO x  is deposited on the entire substrate surface to form a 200 nm thick film, and a resist is coated. The resist is partly removed from the region for the contact hole in a central portion of the spin valve, and after etching by RIE, the resist is removed entirely. After that, milling is carried out for removal of carbides. Thereafter, the upper electrode  52  (Ta 5 nm/Cu 400 nm/Au 200 nm) and the electrode pad are formed by using a metal mask, thereby to complete the substantial part of the magnetoresistive effect element. 
     With the magnetoresistive effect elements prepared by those two kinds of processes explained above, their electric resistance properties were measured by the four-terminal technique. As a result, no difference in magnetoresistance variable amount AΔR was observed. 
     Therefore, in the explanation given below, representative values of device characteristics will be shown without specifying the process. 
     Resistance of the spin valve film in the magnetoresistive effect element A 0  taken as the comparative example was AR=40 mΩμm 2 . 
     On the other hand, GaAs used in the magnetoresistive effect element A 1  was added with Si donor in the amount to adjust the specific resistance to about 10 Ωcm in an n-type semiconductor. However, the device resistivity still tended to increase, and thickness was thinned as far as possible, namely to 1 nm. Lattice constant of GaAs is 5.653 angstrom, which is approximately twice the lattice constant of (Fe 50 Co 50 ) 95 Cu 5 , and it is advantageous for easier attainment of lattice matching. 
     On the other hand, CoSi and (Fe 10 Co 90 )Si inserted in the magnetoresistive effect elements A 2 , A 3  are both n-type semimetals, having electron concentrations around 1×10 20  cm −3  and 2×10 20  cm −3  and specific resistance values around 150 μmΩcm and 600 μΩcm, respectively. Here is no need of accounting an excessive increase of the device resistivity; however, in order to ensure spin-polarized electrons to move from the ferromagnetic material without being relaxed, the resistance adjustment layer  30  had better be thin, and its thickness was adjusted to 1 nm. 
     As a result of measurement of the area resistivity variable amount AΔR of each magnetoresistive effect element, the following values were obtained. 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 Magnetoresistive effect element 
                 AΔR 
               
               
                   
               
             
            
               
                   
                 A0 
                  1.8 mΩμm 2   
               
               
                   
                 A1 
                 200 mΩμm 2   
               
               
                   
                 A2 
                  80 mΩμm 2   
               
               
                   
                 A3 
                 125 mΩμm 2   
               
               
                   
               
            
           
         
       
     
     As apparent also from the result shown above, the magnetoresistive effect element according to the embodiment of the invention can attain resistance variable amounts as large as a hundred times or more of those of conventional elements, and enables significant improvement of sensitivity. 
       FIG. 3  is a schematic diagram that shows a modification of the same embodiment. Some of components shown here, which are common to those of  FIGS. 1 and 2 , are labeled with common reference numerals, and their detailed explanation is omitted here. 
     In this modification, films are stacked in the order of the lower electrode  54 , base layer  12 , antiferromagnetic layer  14 , pinned layer  16 , nonmagnetic intermediate layer  18 , resistance adjustment layer  30 , free layer  20 , protective layer  22  and upper electrode  52 . Also when the resistance adjustment layer  30  is located between the nonmagnetic intermediate layer  18  and the free layer  20 , the same effect is obtained. 
     Second Embodiment 
     As the second embodiment of the invention, next explained is a magnetoresistive effect element having an insulating layer for enhancing the injection efficiency of spin electrons into the resistance adjustment layer  30 . 
       FIG. 4  is a schematic diagram that shows a cross-sectional structure of the substantial part of the magnetoresistive effect element according to the second embodiment. Some of components shown here, which are common to those of  FIGS. 1 to 3 , are labeled with common reference numerals, and their detailed explanation is omitted here. 
     The magnetoresistive effect element according to the instant embodiment has a structure made by sequentially stacking on the lower electrode  54  the base layer  12 , antiferromagnetic layer  14 , pinned layer  16 , insulating layer  40 , resistance adjustment layer  30 , nonmagnetic intermediate layer  18 , free layer  20 , protective layer  22  and upper electrode  52 . 
     In this embodiment, the sense current I is supplied from the upper electrode  52  in the arrow-marked direction toward the lower electrode  54 . That is, electrons flow from the upper electrode  54  toward the upper electrode  52 . 
     The insulating layer  40  functions to enhance the efficiency of injecting electrons having spins into the resistance adjustment layer  30 . That is, a layer made of an insulator and inserted between the pinned layer  16  made of a ferromagnetic material and the resistance adjustment layer  30  made of a semiconductor or semimetal improves the injection efficiency of spin electrons. 
     In this case, in order to ensure a higher injection efficiency of spin electrons, an insulator as clean as possible is preferably used as the insulating layer  40  (Phys. Rev. Lett. 68, 1387 (1992)). 
     Unlike a TMR element, the instant embodiment does not rely on a tunneling barrier function of the insulating layer  40 . Instead, the insulating layer  40  is preferably thinned to lower its barrier height and thereby prevent an excessive increase of the device resistivity. 
     The Inventors prepared magnetoresistive effect elements B 1 , B 2  and B 3  based on the structure shown in  FIG. 4 , and reviewed them in comparison with the magnetoresistive effect element A 3  according to the first embodiment. 
     Materials and thicknesses of respective layers forming the prepared magnetoresistive effect elements are listed below. 
     
       
         
           
               
             
               
                   
               
               
                 &lt;Magnetoresistive effect elements A3, B1, B2, B3&gt; 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Protective layer 22 
                 Ta 
                 (5 nm) 
               
               
                   
                 Second free layer 20 
                 (Co 86 Fe 14 ) 82 Ni 18   
                 (4 nm) 
               
               
                   
                 First free layer 20 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (2 nm) 
               
               
                   
                 Nonmagnetic intermediate 
                 Cu 
                 (3 nm) 
               
               
                   
                 layer 18 
                   
                   
               
               
                   
                 Resistance adjustment 
                 (Fe 10 Co 90 )Si 
                 (1 nm) 
               
               
                   
                 layer 30 
                   
                   
               
               
                   
                 Pinned layer 16C 
                 (Fe 50 Co 50 ) 95 Cu 5   
                  (3 nm)] 
               
               
                   
                 Pinned layer 16B 
                 Ru 
                 (1 nm) 
               
               
                   
                 Pinned layer 16A 
                 Co 90 Fe 10   
                 (3 nm) 
               
               
                   
                 Antiferromagnetic 
                 PtMn 
                 (15 nm)  
               
               
                   
                 layer 14 
                   
                   
               
               
                   
                 Second base layer 12 
                 Ru 
                 (2 nm) 
               
               
                   
                 First base layer 12 
                 Ta 
                 (5 nm) 
               
               
                   
               
            
           
         
       
     
     The prepared magnetoresistive effect elements A 3 , B 1 , B 2  and  133  were common in the above-indicated structure. Here again, the free layer  20  was a multi-layered structure of the first and second nonmagnetic layers. The pinned layer  16  was a synthetic structure stacking two kinds of ferromagnetic layers on opposite surfaces of a Ru (ruthenium) layer. The base layer  12  was formed as a two-layered structure. 
     Further, in the magnetoresistive effect elements B 1 , B 2  and B 3  according to the instant embodiment, an insulating layer  40  was inserted between the pinned layer  16  and the resistance adjustment layer  30  as shown in  FIG. 4 . Contents of the insulating layer  40  in each element were as follows. 
     
       
         
           
               
             
               
                   
               
             
            
               
                 &lt;Magnetoresistive effect element B1&gt; 
               
            
           
           
               
               
               
            
               
                   
                 Insulating layer 40 
                 NiO x   
               
            
           
           
               
            
               
                 &lt;Magnetoresistive effect element B2&gt; 
               
            
           
           
               
               
               
            
               
                   
                 Insulating layer 40 
                 TaO x   
               
            
           
           
               
            
               
                 &lt;Magnetoresistive effect element B3&gt; 
               
            
           
           
               
               
               
            
               
                   
                 Insulating layer 40 
                 AlO x   
               
               
                   
               
            
           
         
       
     
     For the purpose of preventing an excessive increase of the device resistivity, these oxides used as the insulating layer  40  were formed as extremely thin insulating layers by forming metal layers of the one-atom thickness to the two-atom thickness and then oxidizing them. As their materials, those forming relatively low barrier heights to electrons were selected. 
     Also in this embodiment, no significant difference in device property was observed between the two kinds processes of preparation explained in conjunction with the first embodiment. 
     As a result of measurement of magnetoresistance variable amounts AΔR of the respective magnetoresistive effect elements, the following values were obtained. 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 Magnetoresistive effect element 
                 AΔR 
               
               
                   
               
             
            
               
                   
                 A3 
                 125 
               
               
                   
                 B1 
                 500 mΩμm 2   
               
               
                   
                 B2 
                 800 mΩμm 2   
               
               
                   
                 B3 
                 700 mΩμm 2   
               
               
                   
               
            
           
         
       
     
     As apparent also from the result shown above, the magnetoresistive effect element according to the instant embodiment can attain resistance variable amounts as large as several times or more of those according to the first embodiment, and enables significant improvement of sensitivity. 
       FIG. 5  is a schematic diagram that shows a modification of the second embodiment. Some of components shown here, which are common to those of  FIGS. 1 to 4 , are labeled with common reference numerals, and their detailed explanation is omitted here. 
     This modification is so modified that the direction of the sense current I is reversed to flow from the lower electrode  54  toward the upper electrode  54 . In this case, the respective layers of the element are stacked in the order of, from the bottom, the lower electrode  54 , base layer  12 , antiferromagnetic layer  14 , pinned layer  16 , nonmagnetic intermediate layer  18 , resistance adjustment layer  30 , insulating layer  40 , free layer  20 , protective layer  22 , and upper electrode  52 . In this manner, by locating the insulating layer  40  upstream of the spin electrons injected to the resistance adjustment layer  30 , depending upon the direction of the sense current I, substantially the same effect of improving the injection efficiency can be obtained. 
     Third Embodiment 
     As the third embodiment of the invention, next explained is a magnetoresistive effect element commonly using a layer of a semiconductor or semimetal commonly as a resistance adjustment layer and a nonmagnetic intermediate layer. 
       FIG. 6  is a schematic diagram that shows a cross-sectional structure of the substantial part of the magnetoresistive effect element according to the third embodiment. Some of components shown here, which are common to those of  FIGS. 1 to 4 , are labeled with common reference numerals, and their detailed explanation is omitted here. 
     The magnetoresistive effect element according to the instant embodiment has a structure made by sequentially stacking on the lower electrode  54  the base layer  12 , antiferromagnetic layer  14 , pinned layer  16 , resistance adjustment layer  30 , free layer  20 , protective layer  22  and upper electrode  52 . The resistance adjustment layer  30  used here also functions as a nonmagnetic intermediate layer as well. 
     The common use of the resistance adjustment layer also as the nonmagnetic intermediate layer reduces the number of hetero interfaces having a high probability of spin-flip, and thereby minimizes the loss of spin electrons to enhance the output. However, in order that the nonmagnetic intermediate layer completes its role of interrupting magnetic coupling between the pinned layer  16  and the free layer  20 , it must be thick to a certain degree. Therefore, a semiconductor or a semimetal having a relatively low specific resistance is preferably used as the material of the resistance adjustment layer  30  in this embodiment such that the resistance does not increase excessively even when the film becomes somewhat thick. 
     The Inventors prepared magnetoresistive effect elements C 1 , C 2  and C 3  based on the structure shown in  FIG. 6 , and measured their outputs. 
     Materials and thicknesses of respective layers forming the prepared magnetoresistive effect elements are listed below. 
     
       
         
           
               
             
               
                   
               
               
                 &lt;Magnetoresistive effect elements C1, C2, C3&gt; 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Protective layer 22 
                 Ta 
                 (5 nm) 
               
               
                   
                 Second free layer 20 
                 (Co 86 Fe 14 ) 82 Ni 18   
                 (4 nm) 
               
               
                   
                 First free layer 20 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (2 nm) 
               
               
                   
                 Pinned layer 16C 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (3 nm) 
               
               
                   
                 Pinned layer 16B 
                 Ru 
                 (1 nm) 
               
               
                   
                 Pinned layer 16A 
                 Co 90 Fe 10   
                 (3 nm) 
               
               
                   
                 Antiferromagnetic 
                 PtMn 
                 (15 nm)  
               
               
                   
                 layer 14 
                   
                   
               
               
                   
                 Second base layer 12 
                 Ru 
                 (2 nm) 
               
               
                   
                 First base layer 12 
                 Ta 
                 (5 nm) 
               
               
                   
               
            
           
         
       
     
     The layers shown above are the same as those of the magnetoresistive effect elements A 1  through A 3  and B 1  through  133  according to the first and second embodiments. Here again, the free layer  20  was a multi-layered structure of the first and second nonmagnetic layers. The pinned layer  16  was a synthetic structure stacking two kinds of ferromagnetic layers on opposite surfaces of a Ru (ruthenium) layer. The base layer  12  was formed as a two-layered structure. 
     The resistance adjustment layer  30  also serving as the nonmagnetic intermediate layer was inserted between the pinned layer  16  and the free layer. Material and thickness of the resistance adjustment layer  30  in each element were as follows. 
     
       
         
           
               
             
               
                   
               
             
            
               
                 &lt;Magnetoresistive effect element C1&gt; 
               
            
           
           
               
               
               
               
            
               
                   
                 Resistance adjustment layer 30 
                 GaAs 
                 (2 nm) 
               
            
           
           
               
            
               
                 &lt;Magnetoresistive effect element C2&gt; 
               
            
           
           
               
               
               
               
            
               
                   
                 Resistance adjustment layer 30 
                 CoSi 
                 (3 nm) 
               
            
           
           
               
            
               
                 &lt;Magnetoresistive effect element C3&gt; 
               
            
           
           
               
               
               
               
            
               
                   
                 Resistance adjustment layer 30 
                 (Fe 10 Co 90 )Si 
                 (3 nm) 
               
               
                   
               
            
           
         
       
     
     To accomplish the role of the nonmagnetic intermediate layer to interrupt magnetic coupling between the pinned layer  16  and the free layer  20 , the thickness was adjusted in the range from 2 to 3 nm. 
     Also in this embodiment, no significant difference in device property was observed between the two kinds processes of preparation explained in conjunction with the first embodiment. 
     As a result of measurement of magnetoresistance variable amounts AΔR of the respective magnetoresistive effect elements, the following values were obtained. 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 Magnetoresistive effect element 
                 AΔR 
               
               
                   
               
             
            
               
                   
                 C1 
                 300 mΩμm 2   
               
               
                   
                 C2 
                  80 mΩμm 2   
               
               
                   
                 C3 
                 180 mΩμm 2   
               
               
                   
               
            
           
         
       
     
     Since the resistance adjustment layer  30  was somewhat thick, the device resistivity AR of the element C 1  using GaAs was as high as approximately 30 Ωμm 2 . In contrast, in the elements C 2  and C 3  using semimetals, the device resistivity AR was approximately 100 mΩμm 2 , which is a favorable value. To obtain the device resistivity higher than those of C 2  and C 3 , it is effective to increase the thickness of the semimetal layer used as the resistance adjustment layer  30 , or use a material having a relatively high specific resistance (such as MnSi 1.72 , CrSi 2 , (Cr 1-x Mnx)Si 2 , or the like). 
       FIG. 7  is a schematic diagram that shows a modification of the third embodiment. Here again, some of components that are common to those of  FIGS. 1 to 6  are labeled with common reference numerals, and their detailed explanation is omitted here. 
     In this modification, the resistance adjustment layer  30  is inserted in the nonmagnetic intermediate layer  18 . That is, formed on the lower electrode  54  are the base layer  12 , antiferromagnetic layer  14 , pinned layer  16 , first nonmagnetic intermediate layer  18 A, resistance adjustment layer  30 , second nonmagnetic intermediate layer  30 B, free layer  20 , protective layer  22 , and upper electrode  52  in this order. This structure inserting the resistance adjustment layer  30  in the nonmagnetic intermediate layer  18  also ensures the same effect. Additionally, this structure need not increase the thickness of the resistance adjustment layer  30 , and permits it to be sufficiently thinned in accordance with its material. Therefore, this structure is advantageous for adjusting the device resistivity. 
     Heretofore, the first to third embodiments have been explained in conjunction with specific examples. These specific examples, however, should not be construed to limit the invention. 
     For example, in any of the structures explained above, the same effects can be obtained even when reversing the order of stacking the respective layers. 
       FIGS. 8 and 9  are schematic diagrams that show cross-sectional structures of magnetoresistive effect elements in which the magnetization-free layer  20  is located lower. Here again, some of components that are common to those of  FIGS. 1 to 7  are labeled with common reference numerals, and their detailed explanation is omitted here. 
     The structures shown in  FIGS. 8 and 9  correspond to the first embodiment, but structures having a reversed order of lamination of respective layers can be similarly realized by modifying the second and third embodiments, and the same effects can be obtained therefrom. 
     Also regarding the position for inserting the resistance adjustment layer  30  in the spin valve structure, the invention contemplates other various structures in addition to those illustrated. 
     The structure shown in  FIG. 10  corresponds to the synthetic type element shown in  FIG. 2 , but it is reversed in positional relation between the resistance adjustment layer  30  and the nonmagnetic intermediate layer  18 . This type of structure is also envisaged in the present invention, and ensures the same effects as those explained above. 
     The invention is also applicable to structures in which the pinned layer or the free layer has a multi-layered structure, and ensures the same effects. 
       FIG. 11  is a schematic diagram that shows a cross-sectional structure of a magnetoresistive effect element employing a multi-layered structure. In the magnetoresistive effect element shown here, the pinned layer  16  and the free layer  20  are multi-layered films made by alternately stacking ferromagnetic layers  16 A ( 20 A) and interposed layers  16 B ( 20 B). 
     The interposed layers  16 B ( 20 B) may be made of a nonmagnetic metal, kind of ferromagnetic metal different from that of the ferromagnetic layer  16 A ( 20 A), semiconductor or semimetal. 
     Nonmagnetic metals appropriate for this purpose are Cu, Sc, Ti, Mn, Cu Zn, Zr and Hf, for example. 
     Different kinds of ferromagnetic metals usable for this purpose are, for example, ferromagnetic alloys containing at least one of Fe, Co, Ni, Cr and Mn as their major components. 
     Semiconductors appropriate for this purpose are, for example, Ge, III-V compounds and II-VI compounds. 
     Semimetals usable here are, for example, graphite, As, Sb, Bi, HgTe, HgSe, CoSi, Co 1-x Fe x Si, Co 1-x Ni x Si, Co 1-x Mn x Si, Co 1-x Cr x Si and FeSi. 
     These kinds of multi-layered structures are applicable to all structures already explained as the first to third embodiments, and the invention contemplates them all. 
     Furthermore, the invention contemplates magnetoresistive effect elements having oxide layers as well. 
       FIG. 12  is a schematic diagram that shows a cross-sectional structure of a magnetoresistive effect element including an oxide layer  60  between the free layer  20  and the protective layer  22 . 
       FIG. 13  is a schematic diagram that shows a cross-sectional structure of a magnetoresistive effect element having the oxide film  60  inserted in the pinned layer  16 . 
     In these structures, the oxide layer  60  includes a local portion that serves a path of a current when viewed in parallel to the film plane. For example, the oxide layer  60  may have a current path like a pinhole, or may be a continuous film having a region locally changed in composition to exhibit a high conductivity. By using this kind of oxide layer  60 , a current path confining effect is obtained, and the magnetic flux efficiency and sensitivity are improved more. 
     Also when the oxide layer  60  is inserted in the nonmagnetic intermediate layer  18 , substantially the same current path confining effect is obtained. 
     Furthermore, in any of the above-indicated structures, if one or both of the pinned layer  16  and the free layer  20  is made of a half-metal that does not substantially contribute to conduction of electrons unless they are up-spin electrons, then the magnetoresistive effect is enhanced, and the magnetoresistance variable amount increases. 
     Also regarding the material of the free layer, the invention is not limited to those specific examples. 
     Taking a part of the result of trial preparation and evaluation made by the Inventors about materials of the free layer as an example, explanation will be made below. 
     Based on the structure magnetoresistive effect element A 3  explained in conjunction with the first embodiment, samples D 1  through D 3  different in material and thickness of the free layer  20  and the pinned layer  16 C were prepared and evaluated. 
     Materials and thicknesses of respective layers forming the prepared magnetoresistive effect elements are listed below. 
     
       
         
           
               
             
               
                   
               
               
                 &lt;Magnetoresistive effect element A3&gt; 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Protective layer 22 
                 Ta 
                 (5 nm) 
               
               
                   
                 Second free layer 20 
                 (Co 86 Fe 14 ) 82 Ni 18   
                 (4 nm) 
               
               
                   
                 First free layer 20 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (2 nm) 
               
               
                   
                 Nonmagnetic intermediate 
                 Cu 
                 (3 nm) 
               
               
                   
                 layer 18 
                   
                   
               
               
                   
                 Pinned layer 16C 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (3 nm) 
               
               
                   
                 Pinned layer 16B 
                 Ru 
                 (1 nm) 
               
               
                   
                 Pinned layer 16A 
                 Co 90 Fe 10   
                 (3 nm) 
               
               
                   
                 Antiferromagnetic 
                 PtMn 
                 (15 nm)  
               
               
                   
                 layer 14 
                   
                   
               
               
                   
                 Second base layer 12 
                 Ru 
                 (2 nm) 
               
               
                   
                 First base layer 12 
                 Ta 
                 (5 nm) 
               
               
                   
               
            
           
         
       
     
     The magnetoresistive effect element A 3  was changed in material and thickness of the first and second free layer  20  and only the pinned layer  16 C as follows. 
     
       
         
           
               
             
               
                   
               
               
                 (Magnetoresistive effect element D1) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Second free layer 20 
                 Fe 13 Co 20 Ni 67   
                 (4 nm) 
               
               
                   
                 First free layer 20 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (2 nm) 
               
               
                   
                 Pinned layer 16C 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (3 nm) 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 (Magnetoresistive effect element D2) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Second free layer 20 
                 Fe 13 Co 20 Ni 67   
                 (5.5 nm) 
               
               
                   
                 First free layer 20 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (0.5 nm) 
               
               
                   
                 Pinned layer 16C 
                 (Fe 50 Co 50 ) 95 Cu 5   
                   (3 nm) 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 (Magnetoresistive effect element D3) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Second free layer 20 
                 Fe 13 Co 20 Ni 67   
                 (5.5 nm) 
               
               
                   
                 First free layer 20 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (0.5 nm) 
               
               
                   
                 Pinned layer 16C 
                 (Fe 50 Co 50 ) 95 Cu 5   
                 (0.5 nm) 
               
               
                   
                 Pinned layer 16C 
                 Ni 80 Fe 2o   
                 (2.5 nm) 
               
               
                   
                   
               
            
           
         
       
     
     In the magnetoresistive effect element D 3 , the pinned layer  16 C was prepared in form of a two-layered structure, locating the (Fe 50 Co 50 ) 95 Cu 5  nearer to the free layer  20 . 
     As a result of measurement of the area resistivity variable amount AΔR of each magnetoresistive effect element, the following values were obtained. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Magnetoresistive effect element 
                 AΔR 
               
               
                   
                   
               
             
            
               
                   
                 A3 
                 125 
               
               
                   
                 D1 
                 120 mΩμm 2   
               
               
                   
                 D2 
                 118 mΩμm 2   
               
               
                   
                 D3 
                 110 mΩμm 2   
               
               
                   
                   
               
            
           
         
       
     
     When the element D 1  simply changed in material of the first free layer to Fe 13 Co 20 Ni 67  with the element A 3 , AΔR is 125 mΩμm 2  in A 3  and 120 mΩμm 2  in D 1 , and their difference is not large. 
     However, the change of the first free layer to Fe 13 Co 20 Ni 67  leads to a change of magnetization Mst (saturated magnetization Ms×thickness t) of the free layer from 11.8 nmT of A 3  to 9.4 nmT of D 1 . Moreover, when the ratio of thicknesses was changed, magnetization Mst decreased to 7.75 nmT in the elements D 2  and D 3 . The fact that Mst of the free layer is small demonstrates an improvement of the sensitivity to the external magnetic field. 
     Attention is called to the elements D 1  and D 2  for comparing the effects of changing the ratio between the first and second free layers. 
     In the magnetoresistive effect elements explained above, materials typically used in almost all layers have fcc (face-centered cubic) crystal structures. From the viewpoint of the crystal property, the layers are preferably uniform in crystal structure. 
     When the (Fe 50 Co 50 ) 95 Cu 5  film having the bcc (body-centered cubic) crystal structure was as thin as 0.5 nm, the coercive force Hc of the free layer could be decreased from 200 Oe (oersteds) of the element D 1  to 13 Oe of the element D 2 . At that time, AΔR was 120 mΩμm 2  in the element D 1  and 118 mΩμm 2  in the element D 2 , and there was not a large difference here again. This demonstrates that it is important that the spin polarizability is high at the interface between the nonmagnetic portion and the ferromagnetic portion. 
     Taking this result into consideration, it was assumed that a high output would be obtained also by configuring the pinned layer to include (Fe 50 Co 50 ) 95 Cu 5  only along the interface portion thereof. Actually, AΔR was approximately 110 mΩμm 2  in the element D 3 . In the element D 3 , since the ratio of bcc occupied only a small part of the entire film, the crystal property of the film was improved, and the coercive force Hc of the free layer was further reduced to 8 Oe. 
     As explained above, any of the embodiments of the invention can improve the soft-magnetic property of the free layer, decrease the coercive force and thereby ensure a high output by appropriately adjusting the materials and thicknesses of the magnetization free layer and the magnetization-pinned layer. 
     Next explained is the eighth embodiment of the invention, which is a magnetic recording apparatus having inboard any of the magnetoresistive effect element explained with reference to  FIGS. 1 through 13 . 
       FIG. 14  is a perspective view that shows outline configuration of this kind of magnetic recording apparatus. The magnetic recording apparatus  150  shown here is of a type using a rotary actuator. A magnetic recording medium disk  200  is mounted on a spindle  152  and rotated in the arrow A direction by a motor, not shown, which is responsive to a control signal from a controller of a driving mechanism, not shown. The magnetic recording apparatus  150  shown here may have a plurality of medium disks  200  inboard. 
     The medium disk  200  may be of a “lateral recording type” in which directions of the recording bits are substantially in parallel to the disk surface or may be of a “perpendicular recording type” in which directions of the recording bits are substantially perpendicular to the disk surface. 
     A head slider  153  for carrying out recording and reproduction of information to be stored in the medium disk  200  is attached to the tip of a film-shaped suspension  154 . The head slider  153  supports a magnetoresistive effect element or magnetic head, for example, according to one of the foregoing embodiments of the invention, near the distal end thereof. 
     Once the medium disk  200  rotates, the medium-faced surface (ABS) of the head slider  153  is held floating by a predetermined distance above the surface of the medium disk  200 . Also acceptable is a so-called “contact-traveling type” in which the slider contacts the medium disk  200 . 
     The suspension  154  is connected to one end of an actuator arm  155  having a bobbin portion for holding a drive coil, not shown, and others. At the opposite end of the actuator arm  155 , a voice coil motor  156 , a kind of linear motor, is provided. The voice coil motor  156  comprises a drive coil, not shown, wound on the bobbin portion of the actuator arm  155 , and a magnetic circuit made up of a permanent magnet and an opposed yoke that are opposed to sandwich the drive coil. 
     The actuator arm  155  is supported by ball bearings, not shown, which are located at upper and lower two positions of the spindle  157  and driven by the voice coil motor  156  for rotating, sliding movements. 
       FIG. 15  is a perspective view of a magnetic head assembly at the distal end from an actuator arm  155  involved, which is viewed from the disk. The magnetic head assembly  160  includes the actuator arm  155  having the bobbin portion supporting the drive coil, for example, and the suspension  154  is connected to one end of the actuator arm  155 . 
     At the distal end of the suspension  154 , a head slider  153  carrying the magnetoresistive effect element as explained with reference to  FIGS. 1 through 13  is attached. The suspension  154  has a lead  164  for writing and reading signals, and the lead line  164  is connected to electrodes of the magnetic head incorporated in the head slider  153 . Numeral  165  in  FIG. 15  denotes an electrode pad of the magnetic head assembly  160 . 
     In this embodiment, one of the magnetoresistive effect elements already explained in conjunction with the aforementioned embodiments is used as the magnetoresistive effect element, information magnetically recorded on the medium disk  200  under a higher recording density than before can be read reliably. 
     Heretofore, some embodiments of the invention have been explained with reference to specific examples. However, the invention is not limited to these specific examples. 
     For example, as to laminating configuration of the components composing the magnetoresistive effect element, such as the specific size, shape or positional relationship of the electrode, bias magnetic field applying film or insulating layer can be selected from the known art. The invention encompasses any such changes by persons skilled in the art provided they attain the effects of respective embodiments of the invention. 
     The each components of the magnetoresistive effect element such as the antiferromagnetic layer, magnetically pinned layer, nonmagnetic spacer layer or magnetically free layer can be made of a single layer or made of multiplayer including a plurality of films. 
     When the magnetoresistive effect element according to the present invention is applied to a reproducing head, a recording-reproducing integrated magnetic head may be realized by combining a recording head therewith. 
     Further, the magnetic reproducing apparatus according to the present invention may be of a fixed type in which specific magnetic recording medium is permanently installed, while it may be of a removable type in which the magnetic recording medium can be replaced easily. 
     While the present invention has been disclosed in terms of the embodiment in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modification to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims.