Abstract:
A magnetic field sensor incorporates a plurality of magnetic stripes spaced apart on the surface of a substrate such that the stray magnetic fields at the ends of the magnetic stripes are magnetostatically coupled and the magnetic stripes are magnetized respectively in alternating directions, nonmagnetic conductive material positioned in the spaces between the magnetic stripes and electrodes for passing current crosswise through the plurality of magnetic stripes to detect a change in resistance by the giant magnetoresistive effect (MGR). The invention overcomes the problem of detecting low magnetic fields since the magnetic fields required to saturate magnetic stripes depends on the magnetostatic coupling which in turn can be controlled by the geometry and position of the magnetic stripes in the sensor.

Description:
FIELD OF THE INVENTION 
     This invention relates to magnetoresistive sensors and more particularly to giant magnetoresistive effect (GMR) sensors using controlled magnetostatic coupling to obtain opposite alignment of magnetic regions of soft magnetic materials. 
     BACKGROUND OF THE INVENTION 
     The giant magnetoresistive effect (GMR) depends on having magnetic regions which are not aligned with respect to each other in a zero amplitude magnetic field. When the magnetic regions are at saturation in a magnetic field, the magnetization in the magnetic regions are fully aligned. The GMR of magnetic regions in magnetic saturation is defined as the change in resistance from zero magnetic field to the resistance at magnetic saturation normalized by the zero field resistance. 
     Giant magnetoresistance has been discovered in magnetic multilayers. In a publication by S. S. P. Parkin et al., Phys. Rev. Lett. 64, 2304 (1990), the magnetoresistance in metallic superlattice structures of Co/Ru, Co/Cr, and Fe/Cr was reported Values of ΔR/R of up to 33 percent have been observed in a Fe/Cr superlattice structure. This can be compared to ΔR/R of a few percent for the anisotropic magnetoresistance of a simple permalloy thin film sensor. 
     In a publication by W. P. Pratt et al., Phys. Rev. Lett. 66, 3060 (1991), in magnetic multilayers of Ag/Co, the magnetoresistance with the current flow perpendicular to the layer has the largest change of resistance, for example, near 50 percent as compared to the magnetoresistance of current in the plane of the layer which may have a ΔR/R of 12 percent. Also, in multilayer structures, the magnetic fields required to obtain the large values of ΔR/R are very large because the magnetic field must be sufficient to overcome the antiferromagnetic exchange between the layers. These magnetic fields are much larger than the fringing field of a magnetic transition on a disk or tape representing stored data. 
     In exchange coupled films, the magnetic field required to align the oppositely magnetized regions depends on the strength of the antiferromagnetic exchange between the layers. The magnetic field required to align the oppositely magnetized regions tend to be very large, for example, on the order of 10 kOe. 
     A spin valve is a sandwich structure of two magnetic layers with a nonmagnetic layer between such as described in U.S. Pat. No. 5,159,513 which issued on Oct. 27, 1992 to B. Dieny et al. In a spin valve, one magnetic layer has its magnetic orientation fixed, usually by exchanged coupling. The other magnetic layer is free to switch in the applied field except for its own coercivity (Hc) hysteresis. The resistance of the device is highest when the magnetic fields are oppositely aligned or aligned perpendicularly and the lowest resistance is when the magnetic fields are aligned. The magnitude of the giant magnetoresistive effect in spin valve structures may be seven to nine percent as shown in U.S. Pat. No. 5,159,513 which is not as high as in multilayer structures. 
     The giant magnetoresistive effect has also been reported in granular thin films in a publication by J. Q. Xiao et al., Phys. Rev. Lett. 68, 3749 (1992). These granular thin films consist of small phase separated single domain magnetic particles, for example, Co in Cu, a nonmagnetic conductive matrix. So far, the giant magnetoresistive effect has only been observed in a limited set of materials which phase separate into suitable magnetic and nonmagnetic regions. The magnetization is oriented along the easy axis of each particle which varies randomly from particle to particle. The magnetic field must overcome the magnetocrystalline anisotropy and the shape anisotropy of the Co particles. In addition, if there is any interfacial strain at the Cu/Co interface, there may be an additional anisotropy through the magnetostriction (λ). The magnetic field necessary to overcome the random directions by local anisotropy is on the order of 10 kOe. Also, ΔR/R is smaller than in multilayer structures, probably because the change in alignment is less extreme, being from random to parallel rather than from perpendicular to parallel or antiparallel to parallel. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an apparatus for sensing a magnetic field by the giant magnetoresistive effect (GMR) is described comprising a plurality of magnetic stripes spaced apart on the upper surface of a substrate such that the stray fields at the ends of the magnetic stripes provide a magnetostatic coupling which magnetizes the magnetic stripes in alternating directions in a zero magnetic field, a nonmagnetic conductive material such as copper, positioned in the spaces between the magnetic stripes to form a conductive path between respective stripes, and terminals or electrodes for introducing a current along the conductive path for detecting the change in resistance through the plurality of stripes and conductive paths as a function of magnetic fields applied to the magnetic stripes. The magnetic stripes may be rectangular in shape and spaced apart from one another by at least a 100 Å to prevent any exchange coupling. The magnetic stripes may comprise a soft magnetic material. The magnetostatic coupling between ends of magnetic stripes may be enhanced by positioning transverse magnetic stripes over or abutted to the ends which function as permeable “keepers”. The cross-sectional areas of the magnetic stripes may be less than 1000 Å square. The apparatus is suitable for incorporation in a head for sensing a magnetic disk in a magnetic disk operating system. When the magnetic stripes are magnetized in alternating directions, a high resistance state is measured to current passing through the plurality of magnetic stripes and when a magnetic field causes the magnetic stripes adjacent one another to be magnetized in the same direction, a low resistance state is measured to current passing through the plurality of magnetic stripes. 
     The invention further provides, a method for fabricating a magnetic head comprising the steps of orienting, cutting and polishing or selecting a single crystal substrate having a surface at an angle between 1 and 10° away from a major crystallographic plane, annealing the crystal to produce atomic scale steps on its surface, depositing a ferromagnetic metal such as Fe, Co, or Ni or alloys thereof onto the single crystal substrate surface, overcoating the ferromagnetic metal with a nonmagnetic metal of comparable thickness and planarizing the nonmagnetic metal to form alternating regions of magnetic and nonmagnetic metals on the surface of the substrate. 
     The invention provides a plurality of magnetic stripes of soft magnetic material spaced apart for controlled magnetostatic coupling therebetween to obtain opposite alignment of the magnetization of adjacent stripes in zero magnetic field. 
     The invention further provides an apparatus for sensing a magnetic field wherein the magnetic field required for magnetic saturation depends on the magnetostatic coupling which can be controlled by way of the geometry of the magnetic stripes and their spacing. 
     The invention further provides an apparatus for sensing a magnetic field wherein the magnetic stripes are made of soft magnetic materials such as iron, nickel or alloys thereof having high permeability, low coercive force and small hysteresis loss so that the anisotropy magnetic fields are small and do not dominate the magnetic saturation field as in granular films. The distance between the magnetic regions or between magnetic stripes is large enough such as 100 Å such that the magnetic stripes are not strongly exchanged coupled to the adjacent magnetic stripe respectively. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, objects, and advantages of the present invention will become apparent upon consideration of the following detailed description of the invention when read in conjunction with the drawing in which: 
     FIG. 1 is a first perspective view of a first embodiment of the invention. 
     FIG. 2 is a second perspective view of a first embodiment of the invention. 
     FIG. 3 is a perspective view of a second embodiment of the invention. 
     FIG. 4 is a first top view of FIG.  3 . 
     FIG. 5 is a second top view of FIG.  3 . 
     FIG. 6 is a top view of a third embodiment of the invention. 
     FIG. 7 is a top view of a fourth embodiment of the invention, and 
     FIG. 8 is a perspective view of a fifth embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a magnetic head  10  for sensing a magnetic field is shown. A plurality of magnetic stripes  12  through  15  are spaced apart such as by nonmagnetic conducting stripes  16  through  19 . Magnetic stripes  12  through  15  and nonmagnetic stripes  16  through  19  are positioned adjacent one another, side by side, in electrical contact to one another on substrate  22 . Substrate  22  may be nonmagnetic and nonmetallic such as ceramic, glass, sapphire, quartz, magnesium oxide, semi-insulating such as silicon, silicon germanium, gallium arsenide, silicon-on-insulator or a polymer. Substrate  22  has a lower surface  23  upon which magnetic stripes  12  through  15  and nonmagnetic conductive stripes  16  through  19  are positioned. Magnetic stripe  12  is electrically coupled to electrode  26  which may, for example, extend along surface  23  and wrap around the end of substrate  22 . Nonmagnetic conductive stripe  19  is coupled to electrode  28  which may for example extend along surface  23  and wrap around the end of substrate  22  at the end opposite electrode  26 . Substrate  22  and electrode  26  may be supported by arm  29 . Electrode  28  and substrate  22  may be supported by arm  30 . Arms  29  and  30  function to position magnetic head  10  with respect to magnetic media  32  having an upper surface  33  as shown in FIG. 1 such as transverse or 90° to magnetic media  32  as shown in FIG.  2 . Magnetic media  32  may be for example a magnetic disk having a layer of magnetic material thereon suitable for storing information. Arms  29  and  30  may be rigid and in a fixed relationship to one another. 
     Magnetic stripes  12  through  15  may be made of soft magnetic material such as iron, nickel or alloys thereof having high permeability, low coercive force and small hysteresis loss so that anisotropy fields are small and do not dominate the saturation field of the respective magnetic stripe. The ends of magnetic stripes  12  through  15  are positioned with respect to one another to foster magnetostatic coupling between respective ends of magnetic stripes resulting in odd or even magnetic stripes  12  through  15  being magnetized in opposite directions to respective even or odd magnetic stripes as shown in FIG.  2 . For example, magnetic stripes  12  and  14  are magnetized in a first direction shown by arrows  36  and  37  which are parallel and correspond to the longitudinal axes  38  and  39  respectively. Magnetic stripes  13  and  15  are magnetized in a second direction opposite to the first direction shown by arrows  42  and  43  which are parallel to the longitudinal axes  44  and  45  respectively. 
     The magnetostatic coupling from a first end of magnetic stripe  13  is shown by arrows  48  and  49 . Arrow  48  represents the magnetostatic coupling to a first end of magnetic stripe  12  and arrow  49  represents the magnetostatic coupling to a first end of magnetic stripe  14 . Arrow  50  represents the magnetostatic coupling from a second end of magnetic stripe  12  to a second end of magnetic stripe  13 . Arrow  51  represents the magnetostatic coupling from a second end of magnetic stripe  14  to a second end of magnetic stripe  13 . Arrow  52  represents the magnetostatic coupling from a second end of magnetic stripe  14  to a second end of magnetic stripe  15 . Arrow  53  represents the magnetostatic coupling from a first end of magnetic stripe  15  to a first end of magnetic stripe  14 . Each magnetic stripe may have about equal magnetostatic coupling such as shown by arrows  48  and  49  to the adjacent magnetic stripes  12  and  14 . The number of magnetic stripes may be in the range from 2 to about 10,000. The magnetic stripes  12  through  15  are separated from one another by a distance such as 100 Å which is large enough so that they are not strongly antiferromagnetic exchanged coupled. The external magnetic field with the magnetostatic coupling as shown in FIG. 2 corresponds to an applied magnetic field H of zero shown by arrow  55 . With opposite magnetic alignment of adjacent magnetic stripes  12  through  15 , magnetic head  10  is in a high electrical resistant state between electrodes  26  and  28 . 
     FIG. 1 shows the low electrical resistant state of magnetic head  10  where magnetic stripes  12  through  15  are magnetized in the same direction as shown by arrows  57  in the presence of an applied magnetic field H shown by dashed arrows  58 . The low and high electrical resistance state of magnetic head  10  may be detected by passing an electrical current through the plurality of magnetic stripes and plurality of nonmagnetic conductors by way of electrodes  26  and  28 . Current source  60  provides current over leads  61 , through resistor  62  and over lead  63  to electrode  28 . Current from electrode  26  is coupled over lead  64  back to current source  60 . The voltage across leads  63  and  64  provide an indication of the resistance of magnetic head  10 . 
     Referring to FIG. 1, in operation magnetic media  32  may have information stored therein in track  67  in the form of magnetic domains  68  through  73 , with magnetic domain walls  74 ,  76 , and  79 - 81  there between. As magnetic media is moved as shown by arrow  75 , magnetic domains  68  through  73  pass underneath magnetic head  10  and in close proximity to magnetic stripes  12  through  15 . As magnetic domain  71  passes under magnetic head  10 , fringe magnetic fields shown by arrows  58  are aligned in the same longitunal direction as magnetic stripes  12  through  15  and magnetically saturate magnetic stripes  12  through  15  in the longitudinal direction as shown by arrows  57 . The resistance of the current passing through magnetic stripes  12  through  15  from electrode  28  to electrode  26  or vice-versa will be low due to the giant magnetoresistive effect (GMR). As magnetic domain  72  passes underneath magnetic head  10 , the fringe magnetic field shown by arrows  77  will cause magnetic stripes  12  through  15  to magnetically saturate in the opposite direction. As magnetic stripes  12  through  15  change direction in magnetization, the magnetoresistance state will be high due to the misalignment of the magnetization due to the partial change of magnetic direction experience as magnetic domain  72  moves underneath magnetic head  10 . When magnetic domain  72  is completely underneath magnetic head  10 , fringe magnetic fields shown by arrows  77  are aligned with the longitudinal direction of magnetic stripes  12  through  15  and magnetically saturate magnetic stripes  12  through  15  in the longitudinal direction opposite to that shown by arrows  57 . The electrical resistance through magnetic head  10  via electrodes  26  and  28  will be low due to the giant magnetoresistive effect (GMR). Arrows  78  show the direction of fringe magnetic fields for magnetic domain  73  which may be in the same direction as magnetic domain  72 . When magnetic head  10  moves from being over magnetic domain  72  to being over magnetic domain  73 , the electrical resistance through magnetic head  10  via electrodes  26  and  28  will remain low as magnetic stripes  12  through  15  will remain magnetically saturated in the same direction as when magnetic head was over magnetic domain  72 . 
     The magnetic field to be sensed such as shown by arrows  58  in FIG. 1, may be applied in the plane of the device i.e., parallel to surface  23  of which magnetic stripes  12  through  15  are positioned and through magnetic stripes  12  through  15 . The electrical resistance between electrodes  26  and  28  will decrease until magnetic stripes  12  through  15  are saturated in the direction of the applied magnetic field which may be 30 Oe or less as shown by arrows  58  with respect to magnetic domain  70  which is the low GMR state. 
     Referring to FIG. 2, magnetic head  10  is positioned so that the magnetic stripes  12 - 15  are aligned transverse to surface  33  of magnetic media  32  to intercept transverse fringe magnetic fields shown in FIG. 1 from magnetic domains  71  and  72  at or near domain wall  79 . Magnetic media  32  and more particularly track  67  is moving underneath magnetic head  10 . The vertical or transverse (vertical) component of the magnetic domain shown by arrows  58  and  77  in FIG. 1 cause magnetic stripes  12 - 15  to be magnetically aligned in parallel lowering the resistance of magnetic head  10 . For example, when the magnetic stripes  12 - 15  are approaching domain wall  79  but are still in the region of magnetic domain  71  where the fringe fields, shown by arrows  58  in FIG. 1, are parallel to surface  33 , the magnetic stripes will be alternately magnetized due to magnetostatic coupling from adjacent magnetic stripes. When the fringe magnetic fields become vertical or transverse upon approaching the end of magnetic domain  71  near domain wall  79  as shown by arrows  58  in FIG. 1, the magnetization of magnetic stripes  12 - 15  will be directed in the down direction as shown by arrow  36 . Magnetic head  10  will be in the low resistance state with the magnetization of magnetic stripes  12 - 15  aligned parallel. 
     As media  32  moves domain wall  79  past magnetic stripes  12 - 15 , the magnetic stripes will be magnetized in the down direction near domain wall  79  as shown by arrows  17  in FIG.  1 . As media  32 , domain wall  79 , moves way past magnetic stripes  12 - 15 , the fringing magnetic fields of domain  72  will be parallel to surface  33  and there will be no vertical or transverse magnetic component to magnetize magnetic stripes  12 - 15 . Magnetic head  10  will be in the high resistance state. 
     FIG. 3 shows an alternate embodiment of the invention where in addition to the plurality of magnetic stripes  12  through  15  and nonmagnetic conducting stripes  16  through  19  on substrate  22 ′, there are magnetic keepers  82  and  83  positioned over the ends of the magnetic stripes  12  through  15  as shown in FIG.  3 . In FIG. 3 like references are used for functions corresponding to the apparatus of FIGS. 1 and 2. Keepers  82  and  83  function to strengthen or reinforce the magnetostatic coupling connecting the ends of stripes  12  through  15 . 
     For optimal performance, a nonmagnetic electrically insulating spacer  84  must separate magnetoresistive stripes  12 - 15 , together with the intervening nonmagnetic conductors  16 - 19 , from the two keepers  82  and  83 . Spacer  84  serves to (1) prevent exchange stiffness coupling which would tend to align the stripe magnetizations in the same direction, thus counteracting the beneficial keeper effect, and (2) prevent the keepers, if conducting, from short-circuiting magnetoresistive stripes  12 - 15 . Spacer  84  thickness may be in the range from about 50 Å to about 200 Å and is optimally about 100 Å in thickness and needs no lithography since it can blanket over magnetic stripes  12 - 15  and nonmagnetic conductive stripes  16 - 19 . 
     FIG. 4 is a first top view of FIG. 3 showing the magnetic fields and magnetic stripes  12  through  15 , non magnetic stripes  16 - 19  of substrate  22 ′, and keepers  82  and  83 . The magnetic flux carried by each magnetic stripe  12  through  15  respectively is divided in two parts at its ends, each part closing through one of the neighboring magnetic stripes. Therefore, the saturation or magnetic flux capacity of each keeper  82  and  83  should be one half of the saturated magnetic flux capacity of stripes  12  through  15  respectively. In FIG. 4, flux paths  86  and  87  are shown passing through magnetic stripe  13  with flux path  86  passing through magnetic stripe  12  and flux path  87  passing through magnetic stripe  14 . Flux paths  87  and  88  pass through magnetic stripe  14  in the opposite direction of flux paths  87  and  86  passing through magnetic stripe  13 . Flux path  88  passes through magnetic stripe  15 . 
     Magnetic stripe  15  has flux paths  88  and  89  passing through it in opposite directions as flex parts  88  and  87  in magnetic stripe  14 . Flux path  89  also passes through magnetic stripe  20 . 
     Referring to FIG. 5, a magnetic field may be applied perpendicular to the longitudinal axis of the magnetic stripe such as perpendicular to axes  38  and  44  of magnetic stripes  12  and  13  shown on FIG.  5 . An applied magnetic field H shown by arrow  95  perpendicular to the longitudinal axis will produce parallel alignment of the magnetization within magnetic stripes  12  and  13  when the demagnetization field of the magnetic stripe is overcome. The demagnetizing field B is shown in equation 1. 
     
       
         4 πM =4 πM   s   h /( w+h )  (1) 
       
     
     In equation 1, h as shown in FIG. 5 by arrow  93  is equal to the height of the magnetic stripe and W as shown in FIG. 5 by arrow  94  is equal to the width of the magnetic stripe. The term M s  is the saturation magnetization. One advantage of applying a magnetic field H perpendicular to the longitudinal axis of the magnetic stripe is that the magnetic transition within the material is by rotation and therefore faster, more nearly linear, and free of hysteresis. The magnetic field B in a magnetic stripe such as magnetic stripe  12  shown on FIG. 5 is given in equation 2 where H shown by arrow  95  is the applied field and 4 πM is a demagnetization field. 
     
       
           B=H +4 πM   (2) 
       
     
     As shown in FIG. 5, for sufficiently small magnetic stripes with cross sections, less than 1000 square angstroms, domain walls will nucleate thermally. Then the magnetic response will not have a threshold, and hysteresis will be absent. In this regime, the permeable keepers  82  and  83  shown in FIG. 4 will have less influence on the behavior of the magnetic stripes. Statistical correlation between positions of mutually attractive north (N) and south (S) magnetic domain walls will tend to preserve antiparallelism of neighboring magnetic stripe regions by way of magnetic flux paths in and between magnetic stripes  12  and  13  shown in FIG. 5 by arrows  96  through  101 . Also, the magnetostatic coupling between magnetic stripes depends on the spacing between the magnetic stripes. The magnetic stripes will however be spaced to prevent exchange coupling. 
     Referring to FIG. 6, a magnetic array  110  of magnetic stripes  103  through  108  is shown spaced apart on surface  23  of substrate  22  which are generally parallel to one another. Magnetic stripes  103  through  108  may be spaced apart by a first distance shown by arrow  109 . Magnetic stripes  111  through  114  are shown spaced apart, generally parallel to one another and transverse to and over lapping magnetic stripes  103  to  108 . Magnetic stripes  111  through  114  may have a spacing from one another shown by arrow  115 . Non magnetic stripes  181  through  185  fill the space between magnetic stripes  103  and  108  to provide an electrical current path through magnetic stripes  103  through  108 . Crossed or over lapping magnetic stripes  111  through  114  function as permeable keepers as permeable keepers  82  and  83  in FIG.  4 . 
     For optimal performance, a nonmagnetic electrically insulating spacer  116  must separate magnetoresistive stripes  103 - 108 , together with the intervening non-magnetic stripes  181 - 185 , from magnetic stripes  111 - 114  which function the same as keepers  82  and  83  in FIG.  3 . 
     The magnetic stripes  103  through  108  have segments between intersections or cross stripes  111  through  114  to provide independent flux paths some as shown in FIG.  4 . For example magnetic stripe segment  118  of magnetic stripe  104  has a flux path similar as shown for magnetic stripe  13  in FIG.  4 . The magnetic flux shown by arrow  119  divides at cross magnetic stripe  111  with about one half of the magnetic flux going down shown by arrow  120  and one half of the magnetic flux going up shown by arrow  121 . The path of flux  120  follows magnetic stripe  105  and crossed magnetic stripe  112  shown by arrows  122  and  123 . The path of flux  121  is over magnetic stripe  103  and crossed magnetic stripe  112  shown by arrows  124  and  125 . The flux paths are formed by the magnetostatic coupling between cross magnetic stripes  111  and  112  to magnetic stripes  103  and  104  where they cross over. A magnetic field H may be applied in the plane of magnetic stripes  103  through  108  as shown by arrow  128  which will cause the magnetic field within magnetic stripes  103  through  108  to be aligned parallel and thus have lower resistance with respect to current passing through the array. 
     In one electrical arrangement for detecting the change in resistance across magnetic array  110  would be to have cross magnetic stripes  111  through  114  insulated from magnetic stripe  103  to  108  and to have conductive nonmagnetic material  181  through  185  between stripes  103  through  108  as shown in FIG.  6 . The outside current could be applied by way of leads  131  and  132  across magnetic array  110 . When the magnetization in magnetic stripe  103  through  108  are aligned parallel, the magnetic array  110  will be in its low resistance state. When the magnetization is oppositely aligned from stripe segment to stripe segment as shown in FIG. 6 by the arrows  119 ,  122  and  124 , magnetic array  110  will be in the high resistance state. 
     FIG. 7 shows a top view of magnetic device  136  for sensing a magnetic field. Device  136  consists of a substrate  137  having a magnetic layer  138  formed thereover. Magnetic layer  138  has nonmagnetic regions  140  therein which may be formed by diffusing germanium or silicon into nickel, cobalt or alloys thereof which destroys the magnetic moment therein. Magnetic layer  138  is ferromagnetic. Arrows  143  through  146  show a flux path formed around nonmagnetic region  147 . As is illustrated in FIG. 7, the flux path is completely contained within the magnetic layer  138  without penetrating into the nonmagnetic region  147 . The magnetic flux around nonmagnetic region  148  is shown by arrows  149  through  152 . Similarly, the magnetic flux around the nonmagnetic region  148  is also completely contained within the magnetic layer  138  without penetrating into the nonmagnetic region  148 . Nonmagnetic regions may be sub-lithographic in dimension for example presently less than 350 nm. Nonmagnetic region  140  may be produced by bombarding a nickel-cobalt alloy layer having a film of germanium thereover with 100 KV Ge ions. 
     In operation of magnetic device  136  shown in FIG. 7, electrical current may be applied to magnetic layer  138  by way of leads  154  and  155 . When substantially no magnetic field H is applied, the magnetic flux paths around nonmagnetic region  140  will cause device  136  to be in the high resistance state. When a magnetic field H is applied to magnetic layer  138  as shown by arrow  157 , the applied magnetic field will cause the magnetization of magnetic layer  138  including magnetic flux paths around nonmagnetic region  140  to be aligned parallel with arrow  157 . Magnetic device  136  will be in a low resistance state when the magnetization of layer  138  is saturated in a common direction such as in the direction of arrow  157 . 
     Referring to FIG. 1, one method of making a magnetic head  10  will be described. A blanket coating of nickel, iron or cobalt or combinations thereof are deposited on an insulating substrate. The magnetic stripes are defined by lift-off or subtractive lithography. Electron beam or x-ray lithography will be required to obtain spacing between magnetic stripes, of the order of a 100 Å. The magnetic stripes are then overcoated with a high sputtering yield nonmagnetic metal, for example, copper. The structure is then planarized by sputter etching or removing nonmagnetic metal on top of the magnetic stripes. The sputter etching can be done for example with glancing angle ion beam sputtering. 
     While it is possible to make the magnetic stripes by lithography, the resulting device would be larger than the minimum lithographic feature size. Another approach for making magnetic head  10  shown in FIG. 1 is to use structural features which provide magnetic structures of the appropriate size directly as a result of the deposition process. For example, as shown in FIG. 8, a vicinal face of a single crystal substrate is used as a seed layer. Semiconductors such as Si, Ge or GaAs are suitable substrates for the growth of Fe, Ni or Co and their alloys. The vicinal face  161  may be formed by cutting and polishing a single crystal substrate at an angle between 1 to 10° away from a major crystallographic plane and then annealing the crystal substrate  162  to produce atomic scale steps  164  through  167  and surfaces  176 - 180  forming vicinal face  161 . The separation between interplanar steps is determined by the angle of misalignment of vicinal face  161  from a low Miller index plane shown by arrow  175 . Subsequently, magnetic material  170  is deposited under conditions of for example a pressure of 10 −8  Torr or less and a substrate temperature of at least 100° C. so it only grows at the step. In the early stages of growth, the magnetic material  170  grows as isolated particles along the steps  164  through  167 . At a later stage, the particles begin to coalesce in a direction parallel to steps  164  through  167  but have a greater distance perpendicular or transverse to steps  164  through  167 . Magnetic material  170  may be ferromagnetic material, for example, Fe, Co, or Ni or alloys thereof. Substrate  162  may be held at ambient temperature or higher. In this way, an array of parallel magnetic stripes  171  through  174  can be made which is much smaller than the minimum lithographic feature size. Magnetic stripes  171  through  174  are overcoated with a nonmagnetic metal of comparable thickness such as copper. The upper surface of the nonmagnetic metal is planarized so that there are alternating regions of magnetic and nonmagnetic metals on the vicinal face  161 . Magnetic keepers can be deposited through masks generated by conventional lithography at the end of magnetic stripes  171  through  174 . The magnetic keepers should have a lower spontaneous magnetization and/or thickness so that the total magnetic flux carried by the magnetic keeper is approximately one half the flux carried by the respective magnetic stripes  171  through  174  even though the magnetic stripes may have a very different cross sectional area. 
     A magnetic head has been described transverse to the long axis of the magnetic stripe and a means for measuring the electrical resistance of the current flowing through the plurality of magnetic stripes upon the application of the magnetic field which may be 30 Oe or less to the magnetic stripe. 
     Further, a method for fabricating a magnetic head has been described comprising the steps of orienting, cutting and polishing or selecting a single crystal substrate having a surface at an angle between 1 and 10° away from a major crystallographic plane, annealing the crystal to produce atomic scale steps on its surface, depositing a ferromagnetic metal such as Fe, Co, or Ni or alloys thereof onto the single crystal substrate surface with the substrate held at ambient temperature or higher, overcoating the ferromagnetic metal with a nonmagnetic metal of comparable thickness and planarizing the nonmagnetic metal to form alternating regions of magnetic and nonmagnetic metals on the surface of the substrate. 
     While there has been described and illustrated a magnetic head for sensing a magnetic field by the giant magnetoresistive effect (GMR), it would be apparent to those skilled in the art that modifications and variations are possible without deviating from the broad scope of the invention which shall be limited solely by the scope of the claims appended hereto.