Abstract:
In a disk drive GMR or TMR head that uses Ir—Mn—Cr as a pinning layer, Pt—Mn is used as part of the seed layer below the pinning layer to enhance GMR and pinning without deleteriously affecting other head characteristics and to improve head thermal stability.

Description:
I. FIELD OF THE INVENTION  
       [0001]     The present invention relates in general to magnetoresistive devices, and more particularly to magnetoresistive devices that use exchange-coupled antiferromagnetic/ferromagnetic (AF/F) structures, such as current-in-the-plane (CIP) read heads and current-perpendicular-to-the-plane (CPP) magnetic tunnel junctions and read heads.  
       II. BACKGROUND OF THE INVENTION  
       [0002]     In magnetic disk drives, data is written and read by magnetic transducers called “heads.” The magnetic disks are rotated at high speeds, producing a thin layer of air called an air bearing (AB). The read and write heads are supported over the rotating disk by an air bearing surface (ABS), where they either induce or detect flux on the magnetic disk, thereby either writing or reading data. Layered thin film structures are typically used in the manufacture of read and write heads. In write heads, thin film structures provide high magnetic flux to produce recorded magnetic bits on a recording disk with high areal density, which is the amount of data stored per unit of disk surface area, and in read heads they provide high resolution.  
         [0003]     Some read heads in magnetic disk drives use so-called current-in-plane (CIP) magnetoresistive principles, a common example of which is a device that uses an exchange-coupled structure and that is known as a spin-valve (SV) type of giant magnetoresistive (GMR) sensor. The SV GMR head has two ferromagnetic layers separated by a very thin nonmagnetic conductive spacer layer, typically copper, wherein the electrical resistivity for the sensing current in the plane of the layers depends upon the relative orientation of the magnetizations in the two ferromagnetic layers. The direction of magnetization or magnetic moment of one of the ferromagnetic layers (the “free” layer or stack) is free to rotate in the presence of the magnetic fields from the recorded data, while the other ferromagnetic layer (the “fixed” or “pinned” layer or stack) has its magnetization fixed by being exchange-coupled with an adjacent antiferromagnetic layer. The pinned ferromagnetic layer and the adjacent antiferromagnetic layer form an exchange-coupled structure.  
         [0004]     Another type of magnetoresistive device that may be used to establish a read head is a current-perpendicular-to-the-plane (CPP) spin valve GMR sensor. The CPP spin valve read head is structurally similar to the widely used CIP spin valve read head, with the primary difference being that the sense current is directed perpendicularly through the interfaces between the two ferromagnetic layers and the nonmagnetic spacer layer.  
         [0005]     In either case, within the scope of the present invention, it is understood that it is desirable to increase the amount of giant magnetoresistance (GMR) in spin valves, particularly those that use Ir—Mn or Ir—Mn—Cr as the pinning layer, without deleterious side effects such as degraded magnetic pinning or decreased magnetic softness of the free layer. With these recognitions in mind, the invention herein is provided.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention may be applied to bottom single and dual current in plane and current perpendicular to plane GMR sensors and bottom single and dual TMR sensors.  
         [0007]     A magnetoresistive sensor structure has a magnetically pinned stack and a pinning layer including Ir—Mn (preferably, Ir—Mn—Cr) that serves to magnetically pin the pinned stack. A seed stack that includes a thin layer of Pt—Mn is provided.  
         [0008]     In one non-limiting implementation the seed stack includes a Ni—Fe—Cr layer covered by a Ni—Fe layer, and in this embodiment the layer of Pt—Mn covers the Ni—Fe layer. In another non-limiting implementation the layer of Pt—Mn is covered by a Ni—Fe—Cr layer that in turn is covered by a Ni—Fe layer. The layer of Pt—Mn can be between one and ten Angstroms thick and preferably is five Angstroms thick, which is significantly thinner than its critical thickness of about 90 Angstroms, above which Pt—Mn can be transformed upon annealing from FCC paramagnetic phase to L1 0  ordered antiferromagnetic phase and can itself act as a pinning layer.  
         [0009]     In another aspect, a method for making a magnetoresistive sensor structure includes forming a seed stack including at least one layer of Pt—Mn, and depositing onto the seed stack an antiferromagnetic layer that includes Ir—Mn—Cr. The antiferromagnetic layer may be deposited onto a sufficiently preheated seed stack to promote relatively large grain size and/or ordering of Ir—Mn—Cr from disordered antiferromagnetic FCC phase to ordered antiferromagnetic L1 2  phase, which enhances pinning.  
         [0010]     In still another aspect, a magnetic recording sensor includes a free stack, a pinned stack, and a barrier between the free stack and pinned stack. An Ir—Mn—Cr layer provides magnetic pinning for the pinned stack, and a seed stack underlies the Ir—Mn—Cr layer. The seed stack includes means for promoting grain growth and interfacial smoothness in the Ir—Mn—Cr layer.  
         [0011]     In another aspect, a magnetic storage device includes a spindle rotating a magnetic recording disk and a slider juxtaposed with the disk. The slider has at least one magnetic head and is supported by a suspension coupled to an actuator arm, the arm in turn being rotatably positioned by an actuator. The head includes a magnetically pinned stack, a pinning layer including Ir—Mn and magnetically pinning the pinned stack, and a seed stack comprising a layer of Pt—Mn.  
         [0012]     In another aspect, a magnetoresistive sensor includes a free stack, a pinned stack, and a barrier between the free stack and pinned stack. An Ir—Mn—Cr layer provides magnetic pinning for the pinned stack, and a seed stack underlies the Ir—Mn—Cr layer. The seed stack includes means for promoting grain growth and interfacial smoothness in the Ir—Mn—Cr layer.  
         [0013]     The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a schematic plan view of a hard disk drive, showing one non-limiting environment for the present invention;  
         [0015]      FIG. 2  is an elevational view of a first embodiment of a non-limiting device made in accordance with the present invention;  
         [0016]      FIG. 3  is an elevational view of a second embodiment of a non-limiting device made in accordance with the present invention; and  
         [0017]      FIGS. 4-7  are graphs showing various characteristics of non-limiting devices made in accordance with present principles, with the various characteristics plotted as the ordinate versus Pt—Mn layer thickness as the abscissa. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     Referring initially to  FIG. 1 , a magnetic disk drive  30  includes a spindle  32  that supports and rotates a magnetic disk  34 . The spindle  32  is rotated by a spindle motor that is controlled by a motor controller which may be implemented in the electronics of the drive. A slider  42  has a combined read and write magnetic head  40  and is supported by a suspension  44  and actuator arm  46  that is rotatably positioned by an actuator  47 . The head  40  may be a GMR or MR head or other magnetoresistive head. It is to be understood that a plurality of disks, sliders and suspensions may be employed. The suspension  44  and actuator arm  46  are moved by the actuator  47  to position the slider  42  so that the magnetic head  40  is in a transducing relationship with a surface of the magnetic disk  34 . When the disk  34  is rotated by the spindle motor  36  the slider is supported on a thin cushion of air known as the air bearing that exists between the surface of the disk  34  and an air bearing surface (ABS) of the head. The magnetic head  40  may then be employed for writing information to multiple circular tracks on the surface of the disk  34 , as well as for reading information therefrom. To this end, processing circuitry  50  exchanges signals, representing such information, with the head  40 , provides spindle motor drive signals for rotating the magnetic disk  34 , and provides control signals to the actuator for moving the slider to various tracks. The components described above may be mounted on a housing  55 .  
         [0019]     Now referring to  FIG. 2 , the head  40  which is manufactured using the process of the present invention includes a lower magnetic shield  60  that may be made of, e.g., Ni—Fe or other suitable material. On top of the lower shield  60  is a G1 insulation layer  62  that may be made of Al 2 O 3 . This is followed by a seed stack  64 .  
         [0020]     In the embodiment shown in  FIG. 2 , in CIP GMR applications the seed stack  64  includes a lowest layer  66  that may be made of, e.g., AlO x  that, in a non-limiting embodiment, may have a thickness of thirty Angstroms. For CPP GMR or TMR applications, the seed stack  64  does not include AlO x  but instead is built on the bottom shield. In any case, in order going up from either the layer  66  or the bottom shield as appropriate for the particular application are a Ni—Fe—Cr sublayer  68  and a Ni—Fe sublayer  70 . These sublayers  68 ,  70  in non-limiting embodiments may have respective thicknesses of thirty two Angstroms and four Angstroms.  
         [0021]     In accordance with present principles, in the preferred embodiment of  FIG. 2 a  layer  72  of Pt—Mn is deposited on the Ni—Fe sublayer  70 . In preferred embodiments the thickness of the Pt—Mn layer  72  is five Angstroms, and more generally may be between one and eight Angstroms. Only one Pt—Mn layer need be used in the seed stack.  
         [0022]     Referring briefly to the alternate embodiment of  FIG. 3 , as shown instead of disposing the Pt—Mn layer  72  between the Ni—Fe layer  70  and pinning layer  74  as is done in  FIG. 2 , the Pt—Mn layer  72  in  FIG. 3  is disposed just under the Ni—Fe—Cr layer  68 . The present invention has found, however, that it is not preferred to interpose the Pt—Mn layer between the Ni—Fe—Cr layer  68  and the Ni—Fe layer  70  due to degradation of spin valve properties.  
         [0023]     Following the seed layer  64  deposition, the sequence of layers in the spin valve structure includes an Ir—Mn—Cr antiferromagnetic pinning layer  74  of, e.g., seventy five Angstroms thickness, a pinned stack structure  76  that may be, for example but without limitation, CoFe x /Ru/CoFe y  or CoFex/Ru/Co—Fe—B, and a layer  78  that may be, for example but without limitation, a Cu or CuO x  spacer layer in CIP GMR applications, or for example but without limitation a Cu—AlO x  spacer layer for CPP GMR applications. In TMR applications, AlO x  may alternatively be used as a barrier layer  78 , as can a wide range of other materials including, for example, MgO x  or TiO x .  
         [0024]     A free stack structure  80  that may be, for example but without limitation, Co—Fe/Ni—Fe or Co—Fe—B is deposited on the layer  78 . The free stack structure  80  may be covered by a protective capping layer of, e.g., Ta or Ru that may in turn may be topped by a gap in case of CIP GMR applications, or an upper magnetic shield in the case of CPP GMR and TMR applications, in accordance with principles known in the art.  
         [0025]     Formation of the structures shown in  FIGS. 2 and 3  may be undertaken using physical vapor deposition such as sputtering or ion beam deposition, and etching/masking/milling processes known in the art. In preferred non-limiting implementations, the Ir—Mn—Cr pinning layer  74  can be heated after deposition and/or can be deposited onto a heated seed stack, to improve pinning.  
         [0026]     With the above structure and using the preferred five Angstrom thickness of Pt—Mn, the present invention provides for non-degraded GMR, where percent GMR (i.e., the resistance change between the states when the free layer and pinned layer magnetizations are aligned anti-parallel and when they are aligned parallel divided by the structure sheet resistance) is as illustrated in  FIG. 4 , as well as non-degraded DR (where DR=R times DR/R, R is the structure sheet resistance, and DR/R is the GMR ratio) as shown in  FIG. 5 .  
         [0027]     Most importantly, inserting one to ten Angstroms of Pt—Mn layer  72  between Ni—Fe layer  70  and Ir—Mn—Cr layer  74  improves the pinning fields, as measured by H50, as is shown in  FIGS. 6A and 6B . H50 is the applied magnetic field at which the GMR ratio drops by 50%, and serves as a qualitative measure of the strength of pinning of the pinned stack structure. This ten Angstrom Pt—Mn layer  72  also slightly improves blocking temperature between Ir—Mn—Cr and CoFe x , as well as advantageously reduces interlayer coupling, Hf, as is shown in  FIG. 7 . Reduction in interlayer coupling indicates an improved smoothness of the interface between pinned layer  76  and the layer  78 , and/or improved smoothness of the interface between the free layer  80  and layer  78 . Because of the reduced interlayer coupling attributable to the Pt—Mn layer, the layer  78  may be reduced in thickness, which in turn improves GMR ratio and DR in the case of CIP and CPP GMR applications, or reduces barrier resistance without degrading TMR ratio, the analog of GMR ratio in TMR devices, in the case of TMR applications.  
         [0028]     The benefits shown in the above graphs may be attributable to significantly increased Ir—Mn—Cr in-plane grain size, by about forty percent, as determined by X-ray diffraction, and yet with an increased rather than decreased interfacial smoothness, as might be expected when the Ir—Mn—Cr grain size increases. This significantly larger grain size structure is also expected to substantially improve thermal stability of the GMR and TMR spin valve heads due to reduction of grain boundary diffusion.  
         [0029]     In other embodiments, the structures shown in  FIGS. 2 and 3  may be disposed on a substrate to form part of a magnetic random access memory (MRAM) device.  
         [0030]     While the particular SPIN VALVE WITH Ir—Mn—Cr PINNING LAYER AND SEED LAYER INCLUDING Pt—Mn as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”. It is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. Absent express definitions herein, claim terms are to be given all ordinary and accustomed meanings that are not irreconcilable with the present specification and file history.