Abstract:
A giant magnetoresistive stack ( 10 ) for use in a magnetic read head includes a NiFeCr seed layer ( 12 ), a ferromagnetic free layer ( 14 ), a nonmagnetic spacer layer ( 16 ), a ferromagnetic pinned layer ( 18 ), and a CrMnPt pinning layer ( 20 ). The ferromagnetic free layer ( 14 ) has a rotatable magnetic moment and is positioned adjacent to the NiFeCr seed layer ( 12 ). The ferromagnetic pinned layer ( 18 ) has a fixed magnetic moment and is positioned adjacent to the CrMnPt pinning layer ( 20 ). The nonmagnetic spacer layer ( 16 ) is positioned between the free layer ( 14 ) and the pinned layer ( 18 ). The combination of layers with their respective atomic percentage compositions and thicknesses results in a GMR ratio of at least 12%.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Provisional Application No. 60/130,204, filed Apr. 20, 1999 for “Structures to Enhance the GMR Responses and Improve Magnetic Stability Using CrMnPt and NiFeCr Layers” by Zheng Gao, Song S. Xue, and Sining Mao. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a giant magnetoresistive sensor for use in a magnetic read head. In particular, the present invention relates to a giant magnetoresistive read sensor having enhanced giant magnetoresistive responses and improved magnetic stability. 
     Giant magnetoresistive (GMR) read sensors are used in magnetic data storage systems to detect magnetically-encoded information stored on a magnetic data storage medium such as a magnetic disc. A time-dependent magnetic field from a magnetic medium directly modulates the resistivity of the GMR read sensor. A change in resistance of the GMR read sensor can be detected by passing a sense current through the GMR read sensor and measuring the voltage across the GMR read sensor. The resulting signal can be used to recover the encoded information from the magnetic medium. 
     A typical GMR read sensor configuration is the GMR spin valve, in which the GMR read sensor is a multi-layered structure formed of a nonmagnetic spacer layer positioned between a ferromagnetic pinned layer and a ferromagnetic free layer. The magnetization of the pinned layer is fixed in a predetermined direction, typically normal to an air bearing surface of the GMR read sensor, while the magnetization of the free layer rotates freely in response to an external magnetic field. The resistance of the GMR read sensor varies as a function of an angle formed between the magnetization direction of the free layer and the magnetization direction of the pinned layer. This multi-layered spin valve configuration allows for a more pronounced magnetoresistive effect, i.e. greater sensitivity and higher total change in resistance, than is possible with anisotropic magnetoresistive (AMR) read sensors, which generally consist of a single ferromagnetic layer. 
     A pinning layer is typically exchange coupled to the pinned layer to fix the magnetization of the pinned layer in a predetermined direction. The pinning layer is typically formed of an antiferromagnetic material. In antiferromagnetic materials, the magnetic moments of adjacent atoms point in opposite directions and, thus, there is no net magnetic moment in the material. It is desirable for the pinning layer material to have a high blocking temperature, the temperature at which the exchange coupling disappears. It is also desirable for the pinning layer material to have a low annealing temperature, the temperature at which the pinning and pinned layers are exchange coupled during manufacturing, to control magnetic behavior and prevent diffusion between thin layers in the GMR spin valve. 
     A seed layer is typically used to promote the texture and enhance the grain growth of the free layer consequently grown on top of it. The seed layer material is chosen such that its atomic structure, or arrangement, corresponds with the preferred crystallographic direction of the magnetization of the free layer material. 
     One principal concern in the performance of GMR read sensors is the maximum absolute change in resistance of the GMR read sensor, which directly affects the GMR ratio. GMR ratio (the maximum absolute change in resistance of the GMR read sensor divided by the resistance of the GMR read sensor multiplied by 100%) determines the magnetoresistive effect of the GMR read sensor. Ultimately, a higher GMR ratio yields a GMR read sensor with a greater magnetoresistive effect which is capable of detecting information from a magnetic medium with a higher linear density of data. 
     Key determinants of the GMR ratio are the materials used as the pinning layer and as the seed layer in the GMR read sensor. A pinning layer material with a low annealing temperature makes it possible to use a thinner free layer which decreases the resistance of the GMR read sensor which in turn increases the GMR ratio. Also, a seed layer material that causes specular scattering and spin filter effect at the seed layer and free layer interface increases the change in resistance of the GMR read sensor which increases the GMR ratio. 
     Accordingly, there is a need for a GMR read sensor with a higher GMR ratio and for an antiferromagnetic material with a high blocking temperature and a low annealing temperature for use as a pinning layer. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a giant magnetoresistive stack for use in a magnetic read head. The giant magnetoresistive stack includes a NiFeCr seed layer, a ferromagnetic free layer, a nonmagnetic spacer layer, a ferromagnetic pinned layer, and a CrMnPt pinning layer. The free layer has a rotatable magnetic moment and is positioned adjacent to the NiFeCr seed layer. The pinned layer has a fixed magnetic moment and is positioned adjacent to the CrMnPt pinning layer. The spacer layer is positioned between the free layer and the pinned layer. In a first preferred embodiment, the free layer is a NiFe/CoFe bilayer, the spacer layer is formed of copper, and the pinned layer is formed of CoFe. In a second preferred embodiment, the free layer is a NiFe/CoFe bilayer, the spacer layer is formed of copper, and the pinned layer is a CoFe/Ru/CoFe synthetic antiferromagnet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a layer diagram of a first embodiment of a giant magnetoresistive stack of the present invention. 
     FIG. 2 is a graph of the GMR response of the first embodiment of a giant magnetoresistive stack of the present invention. 
     FIG. 3 is a layer diagram of a second embodiment of a giant magnetoresistive stack of the present invention. 
     FIG. 4 is a graph of the GMR response of the second embodiment of a giant magnetoresistive stack of the present invention. 
     FIG. 5 is a graph of the blocking temperature measurement of a CrMnPt pinning layer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a layer diagram of a first embodiment of a giant magnetoresistive (GMR) stack  10  of the present invention. GMR stack  10  includes a seed layer  12 , a free layer  14 , a spacer layer  16 , a pinned layer  18 , and a pinning layer  20 . Seed layer  12  is NiFeCr. Free layer  14  includes a first ferromagnetic material  22 , preferably NiFe, and a second ferromagnetic material  24 , preferably CoFe, and is positioned such that the first ferromagnetic layer  22  is adjacent to seed layer  12 . Pinned layer  18  is a ferromagnetic material, preferably CoFe, and is positioned adjacent to pinning layer  20 . Pinning layer  20  is CrMnPt. Spacer layer  16  is a nonmagnetic material, preferably copper, and is positioned between free layer  14  and pinned layer  18 . 
     The magnetization of pinned layer  18  is fixed in a predetermined direction while the magnetization of free layer  14  rotates freely in response to an external magnetic field emanating from a magnetic medium. The magnetization of pinned layer  18  is pinned by exchange coupling pinning layer  20  with pinned layer  18 . Pinning layer  20  has a blocking temperature of about 340° C. and an annealing temperature of about 230° C. The atomic structure of seed layer  12  is face-centered cubic (fcc) which promotes the [111] crystallographic texture and enhances the grain growth of free layer  14 . The resistance of GMR stack  10  varies as a function of an angle that is formed between the magnetization of free layer  14  and the magnetization of pinned layer  18 . 
     The composition of seed layer  12  is preferably in the range of about Ni(60)Fe(15)Cr(25) to about Ni(48)Fe(12)Cr(40), and more preferably approximately Ni(48)Fe(12)Cr(40), where the numbers in parentheses represent atomic percentage. The thickness of seed layer  12  is preferably in the range of about 20 Å to about 60 Å, and more preferably in the range of about 45 Å to about 50 Å. 
     The composition of the first ferromagnetic layer  22  of free layer  14  is preferably in the range of about Ni(85)Fe(15) to about Ni(80.5)Fe(19.5), and more preferably approximately Ni(82)Fe(18). The thickness of the first ferromagnetic layer  22  of free layer  14  is preferably in the range of about 20 Å to about 100 Å, and more preferably approximately 30 Å. The composition of the second ferromagnetic layer  24  of free layer  14  is preferably approximately Co(90)Fe(10). The thickness of the second ferromagnetic layer  24  of free layer  14  is preferably in the range of about 5 Å to about 25 Å, and more preferably approximately 13 Å. 
     The thickness of spacer layer  16  is preferably in the range of about 20 Å to about 35 Å, and more preferably approximately 24 Å. 
     The composition of pinned layer  18  is preferably approximately Co(90)Fe(10). The thickness of pinned layer  18  is preferably in the range of about 20 Å to about 30 Å, and more preferably approximately 25 Å. 
     The composition of pinning layer  20  is preferably in the range of about Cr(30)Mn(67)Pt(3) to about Cr(50)Mn(35)Pt(15), and more preferably approximately Cr(43)Mn(50)Pt(7). The thickness of pinning layer  20  is preferably approximately 250 Å. 
     FIG. 2 is a graph of the GMR response of GMR stack  10  of the present invention. The graph shows both the GMR ratio and the resistance (Ω) of GMR stack  10  as a function of an applied magnetic field (Oe). The GMR ratio of GMR stack  10  equals 12.9%. The maximum absolute change in sheet resistance of GMR stack  10  equals 2.35 Ω/sq. 
     FIG. 3 is a layer diagram of a second embodiment of a GMR stack  30  of the present invention. GMR stack  30  includes a seed layer  32 , a free layer  34 , a spacer layer  36 , a pinned layer  38 , and a pinning layer  40 . Seed layer  32  is NiFeCr. Free layer  34  includes a first ferromagnetic layer  42 , preferably NiFe, and a second ferromagnetic layer  44 , preferably CoFe, and is positioned such that the first ferromagnetic layer  42  is adjacent to seed layer  32 . Pinned layer  38  is a synthetic antiferromagnet and includes first and second ferromagnetic layers  46  and  50 , both preferably CoFe, and a coupling layer  48 , preferably ruthenium, positioned between first and second ferromagnetic layers  46  and  50 , and is positioned such that the second ferromagnetic layer  50  is adjacent to pinning layer  40 . Pinning layer  40  is CrMnPt. Spacer layer  36  is a nonmagnetic material, preferably copper, and is positioned between free layer  34  and pinned layer  38 . 
     The magnetization of pinned layer  38  is fixed in a predetermined direction while the magnetization of free layer  34  rotates freely in response to an external magnetic field emanating from a magnetic medium. The magnetization of pinned layer  38  is pinned by exchange coupling pinned layer  38  with pinning layer  40 . Pinning layer  40  has a blocking temperature of about 340° C. and an annealing temperature of about 230° C. The atomic structure of seed layer  32  is face-centered cubic (fcc) which promotes the [111] crystallographic texture and enhances the grain growth of free layer  34 . The resistance of GMR stack  30  varies as a function of an angle that is formed between the magnetization of free layer  34  and the magnetization of pinned layer  38 . 
     The composition of seed layer  32  is preferably in the range of about Ni(60)Fe(15)Cr(25) to about Ni(48)Fe(12)Cr(40), and more preferably approximately Ni(48)Fe(12)Cr(40). The thickness of seed layer  32  is preferably in the range of about 20 Å to about 60 Å, and more preferably in the range of about 45 Å to about 50 Å. 
     The composition of the first ferromagnetic layer  42  of free layer  34  is preferably in the range of about Ni(85)Fe(15) to about Ni(80.5)Fe(19.5), and more preferably approximately Ni(82)Fe(18). The thickness of the first ferromagnetic layer  42  of free layer  34  is preferably in the range of about 20 Å to about 100 Å, and more preferably approximately 30 Å. The composition of the second ferromagnetic layer  44  of free layer  34  is preferably approximately Co(90)Fe(10). The thickness of the second ferromagnetic layer  44  of free layer  34  is preferably in the range of about 5 Å to about 25 Å, and more preferably approximately 13 Å. 
     The thickness of spacer layer  36  is preferably in the range of about 20 Å to about 35 Å, and more preferably approximately 24 Å. 
     The compositions of the first and second ferromagnetic layers  46  and  50  of pinned layer  38  are both preferably approximately Co(90)Fe(10). The thicknesses of the first and second ferromagnetic layers  46  and  50  of pinned layer  38  are both preferably in the range of about 15 Å to about 40 Å, and more preferably in the range of about 25 Å to about 30 Å. The thickness of coupling layer  48  of pinned layer  38  is preferably in the range of about 8 Å to about 12 Å. 
     The composition of pinning layer  40  is preferably in the range of about Cr(30)Mn(67)Pt(3) to about Cr(50)Mn(35)Pt(15), and more preferably approximately Cr(43)Mn(50)Pt(7). The thickness of pinning layer  40  is preferably approximately 150 Å. 
     FIG. 4 is a graph of the GMR response of GMR stack  30  of the present invention. The graph shows both the GMR ratio and the resistance (Ω) of GMR stack  30  as a function of an applied magnetic field (Oe). The GMR ratio of GMR stack  30  equals 12.0%. The maximum absolute change in sheet resistance of GMR stack  30  equals 1.9 Ω/sq. 
     FIG. 5 is a graph of the blocking temperature measurement of a CrMnPt pinning layer. The graph shows the strength of the exchange coupling (Oe) as a function of temperature (°C). At 340° C., the strength of the exchange coupling becomes 0 Oe. 
     In summary, the present invention introduces a GMR read sensor with a CrMnPt pinning layer and a NiFeCr seed layer. This configuration exhibits a GMR ratio of at least 12%, the highest ever reported in simple top spin valves. In addition, the CrMnPt pinning layer has a high blocking temperature of about 340° C. to prevent the exchange coupling from disappearing. Also, the CrMnPt pinning layer has a low annealing temperature of about 230° C. to control magnetic behavior and prevent diffusion between thin layers in the GMR read sensor during manufacturing. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.