Abstract:
A ferromagnetic tunneling magneto-resistive head includes a first yoke, divided into a proximal portion and a distal portion across a gap; a second yoke formed so as to resist the first yoke, positioned opposite a magnetic recording medium, a read head gap being formed between the first and second yokes; a tunneling magneto-resistive element including at least one layer of insulating material, the insulating layer being sandwiched between at least two layers of magnetic material, the tunneling magneto-resistive element magneto-electrically converting a signal magnetic field applied via the first yoke and the second yoke by the recording medium making sliding contact with the read head gap; and a pair of electrodes positioned one at each end of the tunneling magneto-resistive element in a direction of layering of the magnetic layers. The tunneling magneto-resistive element is positioned so as to directly contact a proximal portion and a distal portion of the first yoke, with the read head gap, the proximal portion of the first yoke, the tunneling magneto-resistive element, the distal portion of the first yoke and the second yoke together forming an annular magnetic circuit.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to a ferromagnetic tunneling magneto-resistive head, and more particularly, to a ferromagnetic tunneling magneto-resistive head that converts a signal magnetic field recorded on a magnetic recording medium into an electrical signal by coming into sliding contact with the magnetic recording medium.  
           [0003]    2. Description of the Related Art  
           [0004]    Magnetic heads are widely used in magnetic recording/reproduction apparatuses in video recorders, tape recorders and external memory devices for computers. In recent years, with the need to record increasingly large amounts of data, magnetic recording apparatuses capable of accommodating high recording densities are sought.  
           [0005]    Accordingly, the magnetic heads mounted on these types of magnetic recording/reproduction apparatuses also must be capable of reading data from and writing data to a magnetic recording medium at high recording densities. The recording density at which the magnetic head can read data from the recording medium is largely determined by the width of the magnetic head gap and the distance from the recording medium.  
           [0006]    However, the conventional induction-type of magnetic head, in which a coil is wound around the magnetic core, is unsuited for reading and writing data to and from a recording medium at recording densities exceeding 20 Gbit per square inch, which is the level of recording density likely to be achieved in the not-too-distant future. One type of proposed high-density magnetic head capable of accommodating such high recording densities is the anisotropic magneto-resistive effect-type of magnetic head utilizing the anisotropic magneto-resistive effect, referred to below simply as an MR head.  
           [0007]    [0007]FIGS. 1 and 2 show an example of a conventional MR head. FIG. 1 shows a lateral cross-sectional view of a conventional MR head. FIG. 2 shows a plan view of a conventional MR head.  
           [0008]    The MR head shown in the diagrams is configured to use yokes  502 ,  503  to conduct a magnetic flux to the magneto-resistive sensor  504  from a magnetic recording medium  100 , and is a so-called yoke-type MR head.  
           [0009]    As shown in the diagrams, the yoke-type MR head comprises a non-magnetic substrate  501 , atop which are disposed the first yoke  502  (that is, the lower yoke), the second yoke  503  (that is, the upper yoke), the MR sensor  504  and a sensor protective film  508 . The first yoke  502  comprises a proximal portion  502   a  and a distal portion  502   b.  Similarly, the second yoke  503  comprises a proximal portion  503   a  and a distal portion  503   b.    
           [0010]    The first yoke  502  and the second yoke  503  are formed from a ferromagnetic material. Additionally, as can be seen in the diagrams, the proximal portion  503   a  and the distal portion  503   b  of the second yoke  503  are not continuous but are separated across a gap  505 .  
           [0011]    The MR sensor  504  is positioned below the gap  505  formed in the second yoke  503 . Additionally, the MR sensor  504  is connected magnetically to the proximal portion  503   a  and the distal portion  503   b  of the second yoke  503 . Further, the distal portion  502   b  of the first yoke  502  and the distal portion  503   b  of the second yoke  503  are joined and are thus connected magnetically. Additionally, a read gap  506  smaller than the gap  505  in the second yoke  503  is formed between the proximal portion  502   a  of the first yoke  502  and the proximal portion  503   a  of the second yoke  503 .  
           [0012]    As a result, the yoke-type MR head forms a magnetic circuit comprising the proximal portion  503   a  of the second yoke  503 , the MR sensor  504 , the distal portion  503   b  of the second yoke  503  and the first yoke  502 , such that a signal flux from the magnetic recording medium  100  (for example, a magnetic tape) detected at the read gap  506  is conducted to the MR sensor  504  and converted to an electrical signal to obtain a reproduced output. It should be noted that the sensor protective film  508  is formed between the first yoke  502  and the second yoke  503  as well as above the second yoke  503  so as to protect the MR element  504  and the first and second yokes  502 ,  503 .  
           [0013]    However, the reproduced output of an MR head using an MR sensor  504  as described above increases proportionally to the width of the MR element  504 , indicated in FIG. 2 by a double-headed arrow labeled Wmr. Additionally, the reproduced output of the MR head also increases with the extent to which the proximal portion  503   a  of the second yoke  503  and the distal portion  503   b  of the second yoke  503  and the MR sensor  504  overlap in a direction indicated in FIG. 2 by arrow X (hereinafter referred to as overlap width Ws). Accordingly, in order to increase the reproduced output of the MR head it is necessary to increase both the MR width Wmr and the overlap width Ws.  
           [0014]    However, when using the conventional MR sensor  504  described above, increasing the MR width Wmr also increases the resistance of the MR sensor  504 , so that the MR sensor  504  generates an increased amount of noise leading to read errors. In order to avoid this problem of noise, any increase in the width of the MR sensor  504  must be limited to no more than approximately 20 μm, but with such an arrangement it is impossible to obtain the desired high output.  
           [0015]    Moreover, in order to obtain high reproduced output free from noise in the conventional yoke-type MR head, the sensor current flowing through the MR sensor  504  must be prevented from leaking to the proximal portion  503   a  of the second yoke  503  and the distal portion  503   b  of the second yoke  503  so that only the magnetic flux coming from the magnetic recording medium  100  is supplied to the MR sensor  504 . As a result, in the conventional yoke-type MR head, an insulating layer  507  made of material having high relative resistance and high magnetic permeability is formed between the proximal portion  503   a  of the second yoke  503  and the MR sensor  504 , and between the distal portion  503   b  of the second yoke  503  and the MR sensor  504 .  
           [0016]    However, in such a structure, it is difficult to select a suitably effective material for the insulating layer. In addition, it is necessary to form the insulating layer  507  at a point at which the proximal and distal portions  503   a  and  503   b  of the second yoke  503  overlap. Such a formation is difficult to accomplish successfully in view of the extremely small tolerances involved.  
         BRIEF SUMMARY OF THE INVENTION  
         [0017]    Accordingly, it is a general object of the present invention to provide an improved and useful ferromagnetic tunneling magneto-resistive head, in which the drawbacks described above are eliminated.  
           [0018]    Another, further and more specific object of the present invention is to provide an improved and useful ferromagnetic tunneling magneto-resistive head capable of generating a high-output read signal.  
           [0019]    The above-described objects of the present invention are achieved by a ferromagnetic tunneling magneto-resistive head comprising:  
           [0020]    a first yoke, divided into a proximal portion and a distal portion across a gap;  
           [0021]    a second yoke formed so as to resist the first yoke, positioned opposite a magnetic recording medium, a read head gap being formed between the first and second yokes;  
           [0022]    a tunneling magneto-resistive element including at least one layer of insulating material, the insulating layer being sandwiched between at least two layers of magnetic material, the tunneling magneto-resistive element magneto-electrically converting a signal magnetic field applied via the first yoke and the second yoke by the recording medium making sliding contact with the read head gap; and  
           [0023]    a pair of electrodes positioned one at each end of the tunneling magneto-resistive element in a direction of layering of the magnetic layers,  
           [0024]    the tunneling magneto-resistive element positioned so as to directly contact a proximal portion and a distal portion of the first yoke,  
           [0025]    the read head gap, the proximal portion of the first yoke, the tunneling magneto-resistive element, the distal portion of the first yoke and the second yoke forming an annular magnetic circuit.  
           [0026]    According to this aspect of the invention, the tunnel MR element (hereinafter TMR element) is used as an element that converts a signal magnetic field recorded on the recording medium into an electrical signal. The TMR element has a high magneto-resistive variation rate, so a high reproduced output can be obtained even with high recording densities. The TMR element forms a magnetic circuit between the read head gap, the proximal portion of the first yoke, the distal portion of the first yoke, and the second yoke.  
           [0027]    Additionally, the TMR element is disposed so as to directly contact edge surfaces of the proximal portion of the first yoke and the distal portion of the first yoke. As a result, the signal magnetic field flowing from the magnetic recording medium can be prevented from dropping between the proximal portion of the first yoke and the TMR element and between the TMR element and the distal portion of the first yoke. Accordingly, a high reproduced output can be obtained.  
           [0028]    Additionally, the above-described objects of the present invention are also achieved by a ferromagnetic tunneling magneto-resistive head comprising:  
           [0029]    a tunneling magneto-resistive element including at least one layer of insulating material, the insulating layer being sandwiched between at least two layers of magnetic material, the tunneling magneto-resistive element magneto-electrically converting a signal magnetic field to produce an output signal; and  
           [0030]    a pair of electrodes positioned one at each end of the tunneling magneto-resistive element in a direction of layering of the magnetic layers,  
           [0031]    the signal magnetic field being applied to the tunneling magneto-resistive element by the magnetic recording medium coming into direct sliding contact with the tunneling magneto-resistive element.  
           [0032]    According to this aspect of the invention, the tunnel MR element (hereinafter TMR element) is used as an element that converts a signal magnetic field recorded on the recording medium into an electrical signal. The TMR element has a high magneto-resistive variation rate, so a high reproduced output can be obtained even with high recording densities.  
           [0033]    Additionally, the magnetic recording medium is in direct sliding contact with the TMR element, so the signal magnetic field recorded on the magnetic recording medium can be applied directly to the TMR element. As a result, the signal magnetic field loss can be held to a minimum, so a high reproduced output can be obtained.  
           [0034]    Moreover, the TMR element is sandwiched between a pair of electrodes at both ends in a direction of layering of the magnetic layers, so the pair of electrodes act as a reinforcing member reinforcing the TMR element. As a result, wear on the TMR element can be prevented even when the magnetic recording medium is in direct sliding contact with the TMR element. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    These and other objects, features, aspects and advantages of the present invention will become better understood and more apparent from the following description, appended claims and accompanying drawings, in which:  
         [0036]    [0036]FIG. 1 shows a lateral cross-sectional view of a conventional MR head;  
         [0037]    [0037]FIG. 2 shows a plan view of a conventional MR head;  
         [0038]    [0038]FIG. 3 shows a vertical cross-sectional view of a ferromagnetic TMR head according to a first embodiment of the present invention;  
         [0039]    [0039]FIG. 4 shows a plan view of the TMR head according to the first embodiment of the present invention;  
         [0040]    [0040]FIG. 5 shows an expanded lateral cross-sectional view of the TMR sensor of the TMR head according to a first embodiment of the present invention, along the lines X 1 -X 1  in FIGS. 3 and 4;  
         [0041]    [0041]FIG. 6 shows a lateral cross-sectional view of a TMR head according to a first variation of the first embodiment of the present invention;  
         [0042]    [0042]FIG. 7 shows a lateral cross-sectional view of a TMR head according to a second variation of the first embodiment of the present invention;  
         [0043]    [0043]FIG. 8 is a graph showing change in resistance with TMR element size;  
         [0044]    [0044]FIG. 9 is a graph showing a relation between head efficiency on the vertical axis and, on the horizontal axis, a proportion between Ws (the width of the connection of the proximal portion  102   a  of the first yoke  102  to the TMR element  104 ) and Wu (optical read track width);  
         [0045]    [0045]FIG. 10 shows a vertical cross-sectional view of a ferromagnetic TMR head according to a second embodiment of the present invention;  
         [0046]    [0046]FIG. 11 shows a plan view of the TMR head according to the second embodiment of the present invention;  
         [0047]    [0047]FIG. 12 shows a perspective view of the TMR head according to the second embodiment of the present invention;  
         [0048]    [0048]FIG. 13 shows a perspective view of a TMR head according to a first variation of the second embodiment of the present invention;  
         [0049]    [0049]FIG. 14 is a lateral cross-sectional view of a TMR head according to a second variation of the second embodiment of the present invention; and  
         [0050]    [0050]FIG. 15 is a lateral cross-sectional view of a TMR head according to a third variation of the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0051]    A description will now be given of a magnetic head apparatus according to one embodiment of the present invention, with reference to the accompanying drawings. It should be noted that identical or corresponding elements are given identical or corresponding reference numbers in all drawings.  
         [0052]    A description will now be given of a magnetic head according to a first embodiment of the present invention, with reference to the accompanying drawings, in the first instance FIGS. 3 and 4.  
         [0053]    [0053]FIG. 3 shows a vertical cross-sectional view of a ferromagnetic TMR head according to a first embodiment of the present invention. FIG. 4 shows a plan view of the TMR head according to the first embodiment of the present invention.  
         [0054]    By slidingly contacting a magnetic recording medium  100 , the TMR head according to the first embodiment of the present invention converts a signal magnetic field recorded on the magnetic recording medium  100  into an electrical signal. Additionally, the TMR head according to the first embodiment of the present invention applies the signal magnetic field recorded on the magnetic recording medium  100  to a TMR element  104 .  
         [0055]    A description will now be given of the constituent elements of the TMR head described above.  
         [0056]    As shown in the diagrams, the TMR head comprises chiefly a substrate  101 , a first yoke  102 , a second yoke  103 , the TMR element  104 , an upper electrode  105  and a lower pullout electrode  109 , and as such is a yoke-type magnetic head.  
         [0057]    The first yoke  102  comprises a proximal portion  102   a  and a distal portion  102   b . The second yoke  103  similarly comprises a proximal portion  103   a  and a distal portion  103   b . Both the first yoke  102  and the second yoke  103  are composed of a ferromagnetic material.  
         [0058]    Additionally, the proximal portion  102   a  of the first yoke  102  and the distal portion  102   b  of the first yoke  102  are separated across a gap. The TMR element  104  is provided below the gap formed between the proximal portion  102   a  of the first yoke  102  and the distal portion  102   b  of the first yoke  102 . As can be appreciated by those skilled in the art, the TMR element  104  is magnetically connected to the proximal portion  102   a  of the first yoke  102  and the distal portion  102   b  of the first yoke  102 .  
         [0059]    Specifically, a predetermined portion of what is shown in FIG. 3 as the right side of the proximal portion  102   a  of the first yoke  102  overlaps the TMR element  104 . Similarly, a predetermined portion of what is shown in FIG. 3 as the left side of the distal portion  102   b  of the first yoke  102  overlaps the TMR element  104 . As a result of such a configuration, the TMR element  104  is in direct contact with the proximal portion  102   a  of the first yoke  102  and the distal portion  102   b  of the first yoke  102 .  
         [0060]    Further, the distal portion  102   b  of the first yoke  102  and the distal portion  103   b  of the second yoke  103  are joined, and are thus connected magnetically. Additionally, a slight gap that is a read gap  107  is formed at the proximal end between the proximal portion  102   a  of the first yoke  102  and the proximal portion  103   a  of the second yoke  103 .  
         [0061]    As a result, the TMR head forms a magnetic circuit between the first yoke  102  (the proximal portion  102   a  of the first yoke  102 ), the proximal portion  103   a  of the second yoke  103 , the TMR element  104  and the second yoke  103  (the proximal portion  103   a  of the second yoke  103 , the distal portion  103   b  of the second yoke  103 ). The signal magnetic flux from the magnetic recording medium  100  (for example magnetic tape) detected at the read gap  107  is then applied to the TMR element  104  via the proximal portion  102   a  of the first yoke  102 , where the signal magnetic flux is converted into an electrical signal (a read signal). The reproduction signal so generated is then output externally via the upper pullout electrode  108  and the lower pullout electrode  109 . It should be noted that the element protective film  110  is formed atop the gap  106  formed between the first yoke  102  and the second yoke  103 , as well as atop the second yoke  103 , and serves to protect the TMR element  104 , the first and second yokes  102 ,  103  and the electrodes  108 ,  109 .  
         [0062]    A description will now be given of the structure of the TMR sensor  104 .  
         [0063]    [0063]FIG. 5 shows an expanded lateral cross-sectional view of the TMR sensor of the TMR head according to a first embodiment of the present invention, along the lines X 1 -X 1  in FIGS. 3 and 4.  
         [0064]    The TMR sensor  104  has at least one layer of insulating material atop a substrate  101 , with that insulating layer sandwiched between two or more magnetic layers. For illustrative purposes only, the TMR sensor  104  used in the present embodiment, as shown in FIG. 5, uses a single insulating layer indicated by reference numeral  203 .  
         [0065]    Additionally, the TMR element  104  is formed atop the lower pullout electrode  109 , which in turn is formed atop the substrate  101 . The TMR element  104  is composed of the first magnetic layer  202 , the insulating layer  203  and the second magnetic layer  204 .  
         [0066]    At this time, the first magnetic layer  202  and the second magnetic layer  204  are electrically insulated so that no electrical currents other than a tunnel current flows therebetween. In order to achieve this state of insulation, the insulating layer must have a thickness of from 1 nm to 2 nm.  
         [0067]    Additionally, the first magnetic layer  202  is fixedly magnetized in one direction, and must be formed of a material that does not change its direction of magnetization when exposed to different external magnetic fields. In order to achieve such a structure, the first magnetic layer  202  may be made solely of a hard magnetic material magnetized in one direction, or it may be made of layers of antimagnetic film and soft magnetic film.  
         [0068]    By contrast, the second magnetic layer  204 , that is, the free magnetic layer, is formed of a material that changes direction instantaneously upon exposure to an external magnetic field. Additionally, a hard bias film  211  is formed at both lateral ends of the second magnetic layer  204  to apply a bias magnetic field to the second magnetic layer  204  in order to stabilize changes in the direction of magnetization of the second magnetic layer  204 .  
         [0069]    It should be noted that, for purposes of illustration only, the hard bias film  211  used in the present embodiment is made of CoPt. However, as can be appreciated by those of skill in the art, the hard bias film  211  can be made of any electrically conductive magnetic material. Accordingly, in order to ensure that the first magnetic layer  202  and the second magnetic layer  204  are not electrically conductive therebetween, the hard bias film  211  is formed after the insulating film  212  is already formed at both ends of the TMR element  104 .  
         [0070]    The proximal portion  102   a  and the distal portion  102   b  that together form the first yoke  102 , by contacting the TMR  104  as described above, are magnetically connected to each other. More specifically, the first yoke  102  contacts the second magnetic layer  204  (that is, the free magnetic layer) of the TMR element  104 . In other words, the second magnetic layer  204  directly contacts proximate edge portions of the proximal portion  102   a  of the first yoke  102  and the distal portion  102   b  of the first yoke  102 . As a result of such a configuration, the signal magnetic field from the magnetic recording medium  100  is applied directly to the second magnetic layer  204  (that is, the free magnetic layer).  
         [0071]    Specifically, the signal magnetic field of the magnetic recording medium is first conducted to the first yoke  102  (that is, the proximal portion  102   a  of the first yoke  102 ) and then applied via the first yoke  102  to the TMR element  104 . In the structure described above with respect to the present embodiment, the signal magnetic field from the magnetic recording medium  100  is first applied to the second magnetic layer  204  of the TMR element  104 .  
         [0072]    As a result, the second magnetic layer  204  remains unaffected by the insulating layer  203  of the TMR element  104  and the remaining magnetic layer  202  of the TMR element  104 , and the change in the direction of magnetization corresponds accurately to the signal magnetic field characteristics applied from the magnetic recording medium  100  via the first yoke  102 . Accordingly, in the structure according to the present embodiment described above, the TMR head reproduction characteristics can be improved.  
         [0073]    The upper electrode  105  is formed atop the TMR sensor  104  having the structure described above. The upper pullout electrode  108  is connected to the upper electrode  105 . At this time, the resistance between the upper pullout electrode  108  and the lower pullout electrode  109  is 50Ω.  
         [0074]    A description will now be given of a variation of the TMR head shown in FIG. 5, with reference to FIG. 6 and FIG. 7.  
         [0075]    [0075]FIG. 6 shows a lateral cross-sectional view of a TMR head according to a first variation of the first embodiment of the present invention. FIG. 7 shows a lateral cross-sectional view of a TMR head according to a second variation of the first embodiment of the present invention.  
         [0076]    The TMR head shown in FIG. 6, like the TMR head shown in FIG. 5, has a TMR head element  104 A comprising a first magnetic layer  302 , an insulating layer  303  and a second magnetic layer  304 . However, in the present variation the hard bias film  312  uses a magnetic material such as Co—Fe 2 -O 4  or Ba—Fe 12 -O 19 , which have a high relative resistance. By employing such high relative resistance material as the hard bias film  312 , the present variation permits the elimination of the insulating film required by the structure shown in FIG. 5, thus allowing the TMR head to be simplified.  
         [0077]    The TMR head shown in FIG. 7, like the TMR head shown in FIG. 5, has a TMR element  104 B that comprises a first magnetic layer  402 , an insulating layer  403  and a second magnetic layer  404 . However, by employing a magnetic material that is electrically conductive, such as a CoPt combination, for the lower pullout electrode  401 , the TMR head according to the present embodiment equips the lower pullout electrode  401  with the function of the hard bias film.  
         [0078]    Therefore, with the TMR head according to the present variation, the magnetic field leaking from the hard bias film/lower electrode applies a bias to the second magnetic film  404 . With such a structure, the hard bias films  211 ,  312  and insulating film  212  required by the TMR heads shown in FIGS. 5 and 6 can be eliminated, thus further simplifying the structure of the TMR head.  
         [0079]    A description will now be given of a read operation of the TMR head according to the embodiment shown in FIGS. 3 through 5.  
         [0080]    The TMR head according to the present embodiment as described above slides along the magnetic recording medium  100  to generate a reproduction signal. Information in the form of a digital signal is magnetically recorded on the magnetic recording medium  100 , such that when the magnetic recording medium  100  slides relative to the TMR head, the signal magnetic field magnetically recorded on the magnetic recording medium  100  enters the proximal portion  102   a  of the first yoke  102  via the read gap  107 .  
         [0081]    The signal magnetic field entering the proximal portion  102   a  of the first yoke  102  is then applied to the second magnetic layer  204  of the TMR element  104  that bridges the proximal portion  102   a  of the first yoke  102  and the distal portion  102   b  of the first yoke  102 . In so doing, the second magnetic layer  204  is magnetized in a direction that corresponds to the signal magnetic field.  
         [0082]    Next, the signal magnetic field entering the TMR element  104  is led to the distal portion  103   b  of the second yoke  103 , to return to the magnetic recording medium  100  through the second yoke  103  (that is, the proximal portion  103   a  of the second yoke  103  and the distal portion  103   b  of the second yoke  103 ), thus forming an annular magnetic circuit within the TMR head. At this point, the resistance of the TMR element  104  changes according to the relative angle formed between the direction of magnetization of the first magnetic layer  202  of the TMR element  104  and the direction of magnetization of the second magnetic layer  204  of the TMR element  104 .  
         [0083]    As described above, the upper electrode  105  is provided atop the upper surface of the TMR element  104 . The upper pullout electrode  108  is connected to the upper electrode  105 . Additionally, the lower pullout electrode  109  is connected to the lower surface of the TMR element  104 . Accordingly, an electric current flows between the upper pullout electrode  108  and the lower pullout electrode  109  and, by referring to the voltage change generated between the electrodes the digital signal information recorded on the magnetic recording medium  100  can be detected.  
         [0084]    The present embodiment uses the TMR element  104  as a sensor that converts the signal magnetic field recorded on the magnetic recording medium  100  into an electrical signal. The TMR element  104  can provide a-high read output even with high recording densities. Additionally, the TMR element  104  is directly connected to edge surfaces of the proximal portion  102   a  of the first yoke  102  and the distal portion  102   b  of the first yoke  102 . As a result, a drop in the signal magnetic field flowing from the magnetic recording medium  100  between the proximal portion  102   a  of the first yoke  102  and the TMR element  104 , and between the TMR element  104  and the distal portion  102   b  of the first yoke  102 , making it possible to achieve high reproduced output.  
         [0085]    However, the resistance value of the TMR element  104  used in the present embodiment as described above is related to the size of the TMR element  104 . Additionally, a larger resistance of the TMR element  104  means a larger heat level, causing an apparent drop in reproduced output.  
         [0086]    As a result, in the present embodiment as described above, the size of the TMR element  104  is set so that the resistance of the TMR element  104  is no more than 50Ω, thus reducing thermal agitation noise.  
         [0087]    [0087]FIG. 8 is a graph showing change in TMR element resistance with TMR element size. The graph shows a region in which the resistance of the TMR element  104  is no more than 50Ω in relation to a TMR element  104  width Wmr and height h, assuming a TMR element relative resistance of 10 KΩμm 2 . The MR read amp noise level is approximately −180 dBV/ {square root}Hz. In order to not exceed this level, the TMR element  104  resistance must not exceed 50Ω. Accordingly, assuming a relative resistance of the TMR element  104  of 10 KΩ μm 2 , then the width Wmr of the TMR element  104  and the height h of the TMR element must be set so that the resistance R≦50 Ω.  
         [0088]    Additionally, in determining the size of the TMR element  104 , the requirements for a high-output TMR head must be taken into consideration.  
         [0089]    [0089]FIG. 9 is a graph showing a relation between head efficiency on the vertical axis and, on the horizontal axis, a proportion between Ws (the width of the connection of the proximal portion  102   a  of the first yoke  102  to the TMR element  104 ) and Wu (optical read track width).  
         [0090]    The use of the proportion Ws/Wu on the horizontal axis is to check the head efficiency. Additionally, the inclusion of the formula h=α·W s  in the diagram, in the upper left corner of the graph is to show the relation to head efficiency of the relation between a width of the TMR element  104  in a direction perpendicular to the sliding surface of the magnetic recording medium  100  (indicated by arrow h in FIG. 2) and the optical read track width Wu, limited by a coefficient α.  
         [0091]    When examined in light of the considerations described above, the graph shown in FIG. 9 gives the logical head efficiency when the coefficient α is varied from 0.25 to 10. Thus, for example, when the coefficient α=0.25, the ratio Ws/Wu peaks in the vicinity of 25, so a maximum head efficiency of approximately 0.4 can be obtained. To take another example, when the coefficient α=10, the ratio Ws/Wu peaks in the vicinity of 130, so a maximum head efficiency of approximately 0.08 is obtained. In short, as the coefficient α increases, the head efficiency α decreases.  
         [0092]    In order to reproduce the signal magnetic fields recorded at high density on the magnetic recording medium  100  so as to obtain a satisfactory reproduction signal, the head efficiency must be at least 0.05. Accordingly, in order to satisfy such a requirement, the coefficient a must be 10 or less. Additionally, as described above, the formula h=α·W s  is rewritten as α=h/W s . As a result, the condition that “the coefficient α must be α≦10” be rewritten as “the width h of the TMR element  104  in a direction perpendicular to the sliding surface of the magnetic recording medium  100  must be no more than 10 times the optical read track width W s ”.  
         [0093]    That is, by selecting a TMR element  104  size such that the width h of the TMR element  104  in a direction perpendicular to the sliding surface of the magnetic recording medium  100  is no more than  10  times the optical read track width W s , a reproduced output fir the signal magnetic field recorded on the magnetic recording medium  100  can be securely obtained. In light of these conditions, the present embodiment employs the following dimensions: Insulating layer  203  thickness of 2 nm, Wu=5 μm, Wmr=50 μm, Ws=48 μm, h=4 μm.  
         [0094]    A description will now be given of a magnetic head according to a second embodiment of the present invention, with reference to the accompanying drawings, in the first instance FIG. 10, FIG. 11 and FIG. 12.  
         [0095]    [0095]FIG. 10 shows a vertical cross-sectional view of a ferromagnetic TMR head according to a second embodiment of the present invention. FIG. 11 shows a plan view of the TMR head according to the second embodiment of the present invention. FIG. 12 shows a perspective view of the TMR head according to the second embodiment of the present invention.  
         [0096]    In contrast to the TMR head according to the first embodiment of the present invention as described above, the TMR head according to the second embodiment of the present invention does not make use of yokes  102 ,  103  or their equivalent. Instead, the TMR head according to the second embodiment of the present invention directly slides a TMR element  604  against the magnetic recording medium  100 , and is thus a so-called shield-type magnetic head structure.  
         [0097]    The TMR head according to the second embodiment of the present invention chiefly comprises a substrate  101 , a lower magnetic shield film  601 , an upper magnetic shield film  602 , a TMR element  604 , an upper electrode  605  and a lower electrode  606 .  
         [0098]    As with the TMR head according to the first embodiment of the present invention as described above, the substrate  101  is a nonmagnetic or magnetic substrate. On a top portion of the substrate  101  are formed the following, in order: The lower magnetic shield film  601 , a lower insulating film  603   a , the lower electrode  606 , the TMR element  604 , the upper electrode  605 , an upper insulating layer  603   b , and the upper magnetic shield film  602 . Thus the TMR element  604  is sandwiched between the upper electrode  605  and the lower electrode  606 . Further, an element protective film  607  made of nonmagnetic material is provided both atop the upper magnetic shield film  602  and the upper electrode  605  as well as in a space between the upper electrode  605  and lower electrode  606 .  
         [0099]    Additionally, in the TMR head according to the second embodiment of the present invention, the TMR element  604  is exposed to the sliding contact surface  610  of the magnetic recording medium  100 . As a result, when the TMR head comes into sliding contact with the magnetic recording medium  100 , the signal magnetic field recorded on the magnetic recording medium  100  is applied directly to the TMR element  604 . As a result, the TMR head according to the second embodiment of the present invention can reduce the signal magnetic field loss generated by the yokes  102  and  103  necessary to the structure of the TMR head according to the first embodiment of the present invention as described above, thus making higher reproduced outputs obtainable.  
         [0100]    Additionally, as shown in FIGS. 10, 11 and  12 , and as described above, the TMR element  604  is positioned between the electrodes  605 ,  606 , so despite being in direct sliding contact with the magnetic recording medium  100  frictional wear on the TMR  604  can be prevented.  
         [0101]    Though not employed in the present embodiment, those skilled in the art will appreciate that the sliding contact surface  610  of the magnetic recording medium  100  may be curved as well as polished in order to improve sliding contact between the magnetic recording medium  100  and the TMR head.  
         [0102]    However, in the case of the TMR head according to the second embodiment of the present invention as described above, the read gap width is the distance separating the upper magnetic shield  602  and the lower magnetic shield  601 . Yet in the TMR head according to the present embodiment the upper and lower electrodes  605 ,  606  sandwich and completely cover the TMR  604 , so as shown in FIG. 12 the read gap length is the sum of the thicknesses of the lower insulating layer  603   a , the lower electrode  606 , the TMR element  604 , the upper electrode  605  and the upper insulating layer  603   b . The result is that the read gap width is increased and as a consequence the ability to reproduce high-density recordings may be degraded.  
         [0103]    A description will now be given of a TMR head according to a first variation of the second embodiment of the present invention as described above with reference to FIGS. 10, 11 and  12 , with reference to FIG. 13.  
         [0104]    [0104]FIG. 13 shows a perspective view of a TMR head according to a first variation of the second embodiment of the present invention.  
         [0105]    The TMR head according to the first variation of the second embodiment of the present invention has as its object to remedy the problem of expanded read gap as described above. Upper and lower electrodes  705 ,  706  provided above and below a TMR element  704  are positioned behind the TMR element  704 , in contact with a rear edge of the TMR element  704 . As a result, the upper and lower electrodes  705 ,  706  can be kept from the magnetic recording medium  100  and the sliding contact surface  710 .  
         [0106]    As a result, according to the first variation of the second embodiment of the present invention as described above, the relatively thick upper and lower electrodes  705 ,  706  are not exposed to the magnetic recording medium  100  and sliding contact surface  710 . Thus, the read gap width becomes only the sum of the lower insulating layer  703   a , the TMR element  704  and the upper insulating layer  703   b , and accordingly the read gap can be narrowed over that of the TMR head shown in FIG. 12.  
         [0107]    A description will now be given of a TMR head according to a second variation and a third variation of the second embodiment of the present invention as described above, with reference to FIG. 14 and FIG. 15, respectively.  
         [0108]    [0108]FIG. 14 is a lateral cross-sectional view of a TMR head according to a second variation of the second embodiment of the present invention. FIG. 15 is a lateral cross-sectional view of a TMR head according to a third variation of the second embodiment of the present invention. It will be noted that in both variations the upper and lower magnetic shields also function as upper and lower electrodes, respectively.  
         [0109]    The TMR head according to the second variation of the second embodiment, shown in FIG. 14, comprises a lower magnetic shield film (that is, a lower electrode)  801 , atop which are formed a first magnetic layer  803 , an insulating layer  804 , a second magnetic layer  805  and a read gap width adjustment film  806 , in that order. In terms of narrowing the read gap width, the read gap width adjustment film  806  must be made of a nonmagnetic material. In terms of functioning as an electrode, the read gap width adjustment film  806  must be made of an electrically conductive material.  
         [0110]    Additionally, the first magnetic layer  803  and second magnetic layer  805  that together form the TMR element must be completely insulated. If, however, the hard bias film  808  is made of an electrically conductive material such as CoPt, and if the hard bias film  808  is directly formed to both ends of the first magnetic layer  803  and the second magnetic layer  805 , then the first and second magnetic layers  803 ,  805  become conductive.  
         [0111]    As a result, in the TMR head according to the present embodiment, an insulating film  807  is preformed at edge portions of the first magnetic layer  803  and the second magnetic layer  805 , as well as at a bottom of the hard bias film  808 . It should be noted that the insulating film  807  must be made extremely thin and provide effective insulation so as not to interfere with the effect generated by the hard bias film  808 .  
         [0112]    Additionally, the TMR head according to the third variation of the second embodiment, shown in FIG. 15, is characterized by the use of a material that is magnetic but not electrically nonconductive (such as, for example, Co—Fe2-O4 or Ba—Fe12-O19) for the hard bias film  907 . When such a material is used for the hard bias film  907 , the first magnetic layer  903  and the second magnetic layer  905  do not need to be covered by an insulating film, thus simplifying the process of producing the TMR head.  
         [0113]    Further, in the TMR head shown in FIGS. 10 and 12, electrodes or insulating film are provided between the upper and lower magnetic shields, thus complicating the narrowing of the read gap to suitable proportions for high-density recording reproduction. However, with the TMR head shown in FIGS. 14 and 15, the upper and lower magnetic shields also function as upper and lower electrodes, so that by changing the thickness of the respective read gap width adjustment films  806 ,  906  the read gap can be adjusted to a desired width.  
         [0114]    Additionally, the thin film magnetic head of the present invention can also be used with the shield-type MR head as well, so that by conducting the magnetic flux directly from the magnetic recording medium to the TMR element without passing through a yoke the effectiveness of the head can be improved over that of the yoke-type MR head, with increased reproduced output. Those skilled in the art will appreciate that there is the additional advantage that, depending on the TMR element film composition, the read gap can be narrowed with comparative ease as well.  
         [0115]    As can be appreciated by those skilled in the art, the TMR heads according to the above-described embodiments and variations thereof, though formed as dedicated read heads only, can be made into a read/write head by forming a coil in the gap  106  between the first yoke  102  and the second yoke  103  shown in FIG. 3. Additionally, in the case of a shield-type MR head as well, by using for example the upper magnetic shield film  602  of FIG. 10 as the lower magnetic pole of the recording head and forming a thin film recording head atop thereof, the head can be converted into a read/write head.  
         [0116]    The above description is provided in order to enable any person skilled in the art to make and use the invention and sets forth the best mode contemplated by the inventors of carrying out the invention.  
         [0117]    The present invention is not limited to the specifically disclosed embodiments and variations, and modifications may be made without departing from the scope and spirit of the present invention.  
         [0118]    The present application is based on Japanese Priority Application No. 2000-165747, filed on Jun. 2, 2000, the entire contents of which are hereby incorporated by reference.