Patent Application
20090244790
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-323983 filed on Dec. 19, 2008 and No. 2008-088189 filed on Mar. 28, 2008, the entire contents of which are incorporated herein by reference.
The embodiments discussed herein are related to a magnetoresistive element. The embodiments are related to a layered object including an antiferromagnetic layer having a close-packed surface in the (111) surface.
The tunnel-junction magnetoresistive (TMR) element is well known. The tunnel-junction magnetoresistive element includes a reference layer having the magnetization fixed in a predetermined direction irrespective of the influence of the external magnetic field, and a free layer enabling changes in the direction of magnetization under the influence of the external magnetic field. A nonmagnetic layer made of a nonmagnetic material is interposed between the reference layer and the free layer. The electrical resistance changes in accordance with the relative angle between the direction of magnetization in the reference layer and the direction of magnetization in the free layer. An antiferromagnetic layer is utilized to fix the magnetization of the reference layer in a predetermined direction. The antiferromagnetic layer is overlaid on an underlayer. The (111) surface of the crystal are aligned in parallel with the surface of the underlayer in the antiferromagnetic layer.
The utilization of a Heusler alloy is proposed in the field of the tunnel-junction magnetoresistive elements. The reference layer may be made of a Heusler alloy, for example. The Heusler alloy realizes a remarkable difference in the density of states between upspin and downspin at the Fermi surface. Electro conductance of minority and majority spin is metallic and semi conductance, respectively. Therefore, TMR elements with the Heusler alloy are expected to realize a higher magnetoresistance (MR) ratio. In this case, the Heusler alloy is preferably made to establish a crystal having the (002) surface oriented in parallel with the surface of the underlayer. The establishment of such (002) surface requires the minimization of the thickness. The Heusler alloy, which exhibits a high polarizability at the Fermi surface, includes CO2MnAl, CO2MnSi, CO2FeAl, CO2FeSi, CO2FeAl0.5Si0.5, and the like.
According to an aspect of the invention, an magnetoresistive element includes: an underlayer made of a nitride; a pinning layer made of an antiferromagnetic layer overlaid on the underlayer, the pinning layer having the close-packed surface in the (111) surface of crystal, the pinning layer orienting the (002) surface of crystal in parallel with the surface of the underlayer; a reference layer overlaid on the pinning layer, the reference layer having the magnetization fixed in a predetermined direction based on the exchange coupling with the pinning layer; a nonmagnetic layer overlaid on the reference layer, the nonmagnetic layer made of a nonmagnetic material; and a free layer overlaid on the nonmagnetic layer, the free layer made of a ferromagnetic material, the free layer enabling a change in the direction of the magnetization under the influence of an external magnetic field.
There may be provided a specific layered object to realize the magnetoresistive element. The layered object may include: an underlayer made of a nitride; and an antiferromagnetic layer overlaid on the underlayer, the antiferromagnetic layer having the close-packed surface in the (111) surface of crystal, the antiferromagnetic layer orienting the (002) surface of crystal in parallel with the surface of the underlayer.
The object and advantages of the embodiment will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the embodiment, as claimed.
Embodiments of the invention will be explained below with reference to the accompanying drawings.
At least one magnetic recording disk 14 as a storage medium is located in the inner space of the enclosure base 13. The magnetic recording disk or disks 14 are mounted on the driving shaft of a spindle motor 15. The spindle motor 15 drives the magnetic recording disk or disks 14 at a higher revolution speed such as 3,600 rpm, 4,200 rpm, 5,400 rpm, 7,200 rpm, 10,000 rpm, 15,000 rpm, or the like. Here, a so-called perpendicular magnetic recording disk is employed as the magnetic recording disk or disks 14, for example. Specifically, the axis of easy magnetization is set in the direction perpendicular to the surface of the magnetic recording disk 14 in a magnetic layer for recordation on the magnetic recording disk 14.
A carriage 16 is also located in the inner space of the enclosure base 13. The carriage 16 includes a carriage block 17. The carriage block 17 is supported on a vertical support shaft 18 for relative rotation. Carriage arms 19 are defined in the carriage block 17. The carriage arms 19 extend in a horizontal direction from the vertical support shaft 18. The carriage block 17 may be made of aluminum, for example. Extrusion process may be employed to form the carriage block 17, for example.
A head suspension 21 is attached to the front or tip end of the individual carriage arm 19. The head suspension 21 extends forward from the carriage arm 19. A flexure is attached to the head suspension 21. The flexure defines a so-called gimbal at the front or tip end of the head suspension 21. A magnetic head slider, namely a flying head slider 22, is supported on the gimbal. The gimbal allows the flying head slider 22 to change its attitude relative to the head suspension 21. A magnetic head, namely an electromagnetic transducer is mounted on the flying head slider 22.
When the magnetic recording disk 14 rotates, the flying head slider 22 is allowed to receive airflow generated along the rotating magnetic recording disk 14. The airflow serves to generate a positive pressure or lift as well as a negative pressure on the flying head slider 22. The lift of the flying head slider 22 is balanced with the urging force of the head suspension 21 and the negative pressure so that the flying head slider 22 keeps flying above the surface of the magnetic recording disk 14 at a higher stability during the rotation of the magnetic recording disk 14.
A power source such as a voice coil motor, VCM, 23 is coupled to the carriage block 17. The voice coil motor 23 serves to drive the carriage block 17 around the vertical support shaft 18. The rotation of the carriage block 17 allows the carriage arms 19 and the head suspensions 21 to swing. When the individual carriage arm 19 swings around the vertical support shaft 18 during the flight of the flying head slider 22, the flying head slider 22 is allowed to move in the radial direction of the magnetic recording disk 14. The electromagnetic transducer on the flying head slider 22 is thus allowed to cross the data zone defined between the innermost and outermost recording tracks. The electromagnetic transducer on the flying head slider 22 is positioned right above a target recording track on the magnetic recording disk 14.
The slider body 25 may be made of a hard nonmagnetic material such as Al2O3—TiC. The head protection film 26 is made of an insulating, nonmagnetic, relatively soft material such as Al2O3 (alumina). A bottom surface 28 as a medium-opposed surface is defined over the slider body 25 to face the magnetic recording disk 14 at a distance. A flat base surface 29 as a reference surface is defined on the bottom surface 28. When the magnetic recording disk 14 rotates, airflow 31 flows along the bottom surface 28 from the inflow or leading end toward the outflow or trailing end of the slider body 25.
A front rail 32 is formed on the bottom surface 28 of the slider body 25. The front rail 32 stands upright from the base surface 29 near the inflow end of the slider body 25. The front rail 32 extends along the inflow end of the base surface 29 in the lateral direction of the slider body 25. A rear center rail 33 is likewise formed on the bottom surface 28 of the slider body 25. The rear center rail 33 stands upright from the base surface 29 near the outflow end of the slider body 25. The rear center rail 33 is located at the intermediate position in the lateral direction of the slider body 25. The rear center rail 33 extends to reach the head protection film 26. A pair of rear side rails 34, 34 is likewise formed on the bottom surface 28 of the slider body 25. The rear side rails 34, 34 stand upright from the base surface 29 of the bottom surface 28 near the outflow end of the slider body 25. The rear side rails 34, 34 are located along the sides of the slider body 25, respectively. The rear center rail 33 is located in a space between the rear side rails 34, 34.
Air bearing surfaces 35, 36, 37 are defined on the top surfaces of the front rail 32, the rear center rail 33 and the rear side rails 34, respectively. Steps are formed to connect the inflow ends of the air bearing surfaces 35, 36, 37 to the top surfaces of the front rail 32, the rear center rail 33 and the rear side rails 34, respectively. When the bottom surface 28 of the flying head slider 22 receives the airflow 31, the steps serve to generate a larger positive pressure or lift at the air bearing surfaces 35, 36, 37, respectively. Moreover, a larger negative pressure is generated behind the front rail 32 or at a position downstream of the front rail 32. The negative pressure is balanced with the lift so as to stably establish the flying attitude of the flying head slider 22. It should be noted that the flying head slider 22 can take any shape or form different from the described one.
The electromagnetic transducer 27 is embedded in the rear center rail 33 at a position downstream of the air bearing surface 36. The electromagnetic transducer 27 includes a read element and a write element. A tunnel-junction magnetoresistive (TMR) element is employed as the read element. The TMR element is allowed to induce variation in the electric resistance of the tunnel-junction film in response to the inversion of polarization in the applied magnetic field leaked from the magnetic recording disk 14. This variation in the electric resistance is utilized to discriminate binary data recorded on the magnetic recording disk 14. A so-called single-pole head is employed as the write element. The single-pole head generates a magnetic field with the assistance of a thin film coil pattern. The generated magnetic field is utilized to record binary data into the magnetic recording disk 14. The electromagnetic transducer 27 allows the read gap of the read element and the write gap of the write element to get exposed at the surface of the head protection film 26. A hard protection film may be formed on the surface of the head protection film 26 at a position downstream of the air bearing surface 36. Such a protection film covers over the write gap and the read gap exposed at the surface of the head protection film 26. The protection film may be made of a diamond like carbon (DLC) film, for example.
As depicted in
The write element 46, namely the single-pole head, includes a main magnetic pole 47 and an auxiliary magnetic pole 48, exposed at the surface of the rear center rail 33. The main magnetic pole 47 and the auxiliary magnetic pole 48 may be made of a magnetic material such as FeN or NiFe. Referring also to
An underlayer 52 is overlaid on the surface of the auxiliary underlayer 51. The underlayer 52 is made of a nitride. Here, the underlayer 52 is made of NiFeN (nickel iron nitride). The thickness of the underlayer 52 is set at 3.0 nm, for example.
A pinning layer 53 is overlaid on the surface of the underlayer 52. The pinning layer 53 is an antiferromagnetic layer. Here, the pinning layer 53 is made of an IrMn (Iridium Manganese) alloy. The pinning layer 53 has an fcc (face-centered cubic) structure. The fcc structure includes a closed-packed surface corresponding to the (111) surface of crystal. The nitride of the underlayer 52 greatly contributes to establishment of a preferential orientation of the (002) surface in the pinning layer 53 in parallel with the surface of the underlayer 52 as described later in detail. The thickness of the pinning layer 53 is set at 7.0 nm, for example.
A pinned layer 54 is overlaid on the surface of the pinning layer 53. The pinned layer 54 is a ferromagnetic layer. Here, the pinned layer 54 is made of a CoFe (cobalt iron) alloy. The thickness of the pinned layer 54 is set at 1.7 nm, for example. Exchange coupling is established between the pinned layer 54 and the pinning layer 53. The exchange coupling serves to fix the magnetization of the pinned layer 54 in a predetermined direction. It may be ensured that the thickness of the pinning layer 53 made of IrMn is set equal to or larger than 4.0 nm, for example, to establish the exchange coupling.
A nonmagnetic interlayer 55 is overlaid on the surface of the pinned layer 54. The nonmagnetic interlayer 55 is made of a nonmagnetic material. Here, the nonmagnetic interlayer 55 is made of Ru (ruthenium). The thickness of the nonmagnetic interlayer 55 is set at 0.68 nm, for example.
A reference layer 56 is overlaid on the surface of the nonmagnetic interlayer 55. The reference layer 56 is made of a Heusler alloy. Here, the reference layer 56 is made of a CO2MnSi (cobalt manganese silicon) alloy. The thickness of the reference layer 56 is set at 2.5 nm, for example. The Heusler alloy has a predetermined crystalline structure such as the L21 structure, the B2 structure, and the like, for example. The (002) surface is preferentially oriented in the reference layer 56 in parallel with the surface of the nonmagnetic interlayer 55. The reference layer 56 in combination with the pinned layer 54 and the nonmagnetic interlayer 55 establishes a synthetic ferri structure. Exchange coupling is thus induced between the pinned layer 54 and the reference layer 56. The exchange coupling produces an antiparallel relationship between the magnetization of the reference layer 56 and the magnetization of the pinned layer 54. It should be noted that the reference layer 56 may directly be overlaid on the surface of the pinning layer 53. In this case, exchange coupling is induced between the reference layer 56 and the pinning layer 53.
A tunnel barrier layer 57 is overlaid on the surface of the reference layer 56. The tunnel barrier layer 57 is made of an electrically-insulating material. Here, the tunnel barrier 57 is made of MgO (magnesium oxide). The thickness of the tunnel barrier layer 57 is set in a range from 1.0 nm to 1.5 nm, for example.
A free layer 58 is overlaid on the surface of the tunnel barrier layer 57. The free layer 58 is a ferromagnetic layer. Here, the free layer 58 is a CoFeB (cobalt iron boron) layer. The thickness of the free layer 58 is set at 3.0 nm, for example. The free layer 58 enables a change in the direction of the magnetization under the influence of an external magnetic field.
A capping layer 59 is overlaid on the surface of the free layer 58. The capping layer 59 is made of a nonmagnetic metallic material, for example. Here, the capping layer 59 is made of Ta (tantalum). The thickness of the capping layer 59 is set equal to or larger than 3.0 nm, for example. The capping layer 59 can be a Ru (ruthenium) layer or a Ti (titanium) layer. Alternatively, the capping layer 59 may be a layered body including a Ta layer and a Ru layer.
The aforementioned upper electrode layer 44 is overlaid on the capping layer 59. A pair of magnetic domain controlling films 61 is located between the upper electrode layer 44 and the lower electrode layer 43. The tunnel-junction magnetoresistive film 45 is interposed between the magnetic domain controlling films 61 along the bottom surface 28. The magnetic domain controlling films 61 may be made of a hard magnetic material, for example. Here, the magnetic domain controlling films 61 are made of CoCrPt (cobalt chromium platinum alloy), for example. The magnetic domain controlling films 61 are magnetized in a predetermined direction. The magnetization of the magnetic domain controlling films 61 generates a magnetic field across the free layer 58 along the bottom surface 28. The magnetic domains thus have the magnetization in a specific single direction in the free layer 58.
An insulating film 62 is formed between the tunnel-junction magnetoresistive film 45 and each of the magnetic domain controlling films 61. The insulating film 62 is made of Al2O3, for example. The thickness of the insulating film 62 is set in a range from 3.0 nm to 10.0 nm, for example. The insulating film 62 serves to insulate the magnetic domain controlling films 61 from the tunnel-junction magnetoresistive film 45. The insulating film 62 is likewise formed between the lower electrode layer 43 and each of the magnetic domain controlling films 61. The insulating film 62 is made of Al2O3, for example. The thickness of the insulating film 62 is set in a range from 3.0 nm to 10.0 nm, for example. The insulating film 62 serves to insulate the magnetic domain controlling films 61 from the lower electrode layer 43. Consequently, even if the magnetic domain controlling films 61 have electrical conductivity, electrical connection is established between the upper electrode layer 44 and the lower electrode layer 43 only through the tunnel-junction magnetoresistive film 45.
A preferential orientation of the (002) surface in the Heusler alloy as described above results in a remarkably enhanced magnetoresistance (MR) ratio of the tunnel-junction magnetoresistive film 45. This leads to an enhanced sensitivity of the read element 42. The read element 42 of this type thus significantly contributes to an improvement in recording density. Moreover, even if the pinning layer 53 made of IrMn is relatively thin, exchange coupling of a sufficient intensity can be obtained. The underlayer 52 made of a nitride has the same thickness as a conventionally used Ru underlayer. Therefore, space can thus be kept relatively small between the lower electrode layer 43 and the upper electrode layer 44. This results in the enhanced linear resolution of magnetic recordation on the magnetic recording disk 14 along the recording track.
Next, a brief description will be made on a method of making the read element 42 and the write element 46. An Al2O3—TiC substrate is first prepared. A first Al2O3 film is formed on the surface of the Al2O3—TiC substrate. The read element 42 and the write element 46 for the individual flying head slider 22 are formed on the first Al2O3 film. The write element 46 is formed in a conventional manner. After the fabrication of the read element 42 and the write element 46, a second Al2O3 film is formed on the surface of the Al2O3—TiC substrate. The first and second Al2O3 films form the head protection film 26. The individual flying head slider 22 is cut out of the Al2O3—TiC substrate.
The lower electrode layers 43 are formed on the first Al2O3 film at predetermined positions. Sputtering is employed to form the lower electrode layers 43, for example. The lower electrode layers 43 are formed in a predetermined shape. Formed in sequence on the lower electrode layer 43 are a film material for the auxiliary underlayer 51, a film material for the underlayer 52, a film material for the pinning layer 53, a film material for the pinned layer 54, a film for the nonmagnetic interlayer 55, a film material for the reference layer 56, a film material for the tunnel barrier layer 57, a film material for the free layer 58, and a film material for the capping layer 59. Specifically, as depicted in
Photolithography is then applied to shape the tunnel-junction magnetoresistive film 45 out of a layered body of the Ta film 63, the NiFeN film 64, the IrMn film 65, the CoFe film 66, the Ru film 67, the CO2MnSi film 68, the MgO film 69, the CoFeB film 71 and the Ta film 72. As depicted in
The insulating film 62 is then formed on the Al2O3—TiC substrate in a range from 3.0 nm to 10.0 nm thickness. Here, an Al2O3 film is formed, for example. Sputtering is employed to form the insulating film 62. Al2O3 is deposited on the photoresist film 73 and the lower electrode layer 43. A film material for the magnetic domain controlling films 61 is then formed on the insulating film 62. Sputtering is employed to form the film material. Here, a CoCrPt film is formed. The tunnel-junction magnetoresistive film 45 is covered with the CoCrPt film. Lift-off process is applied to remove the insulating film 62 and the CoCrPt film from surface of the tunnel-junction magnetoresistive film 45. In other words, the photoresist film 73 is removed from the surface of the tunnel-junction magnetoresistive film 45.
The surface of the CoCrPt film is subjected to polishing and flattening process. Chemical mechanical polishing (CMP) is employed for the polishing and flattening process. The surfaces of the capping layer 59 and the magnetic domain controlling films 61 are leveled to a continuous surface. The upper electrode layer 44 is formed on the continuous surface. Sputtering is employed for the formation, for example. The upper electrode layer 44 is formed in a predetermined shape. The magnetic domain controlling films 61 are subjected to heating process in a magnetic field. The magnetic domain controlling films 61 are magnetized in a predetermined direction. The read element 42 is in this manner produced.
The inventors have examined the relationship between a nitride layer and an antiferromagnetic layer. The inventors formed simple stacked films that is Ta 3/underlayer 3/IrMn 7/CoFe 4 [nm] on a support substrate. The underlayer was made of NiFe and NiFeN. A Si substrate was used as the support substrate. The partial pressure of N2 gas was set at 73% to form the NiFeN underlayer. The inventors observed the oriented surface of the IrMn pinning layer 53. An X-ray diffractometer using characteristic X rays CuKα rays was employed for the observation. The inventors prepared a comparative example for the observation. The comparative example employed a NiFe underlayer in place of the NiFeN underlayer 52. As depicted in
The inventors have also observed the oriented surface of the CO2MnSi reference layer 56. For the observation, formed in sequence on a glass substrate were a Ta layer of 3.0 nm thickness, a NiFeN layer of 3.0 nm thickness, an IrMn layer of 4.0 nm thickness, a CoFe layer of 1.7 nm thickness, a Ru layer of 0.4 nm thickness, and a CO2MnSi layer of 10.0 nm thickness, in the same manner as described above. As depicted in
The inventors have also observed the oriented surface of the CO2MnSi reference layer 56. For the observation, formed in sequence on a glass substrate were a Ta layer of 3.0 nm thickness, a NiFeN layer of 3.0 nm thickness, an IrMn layer of 4.0 nm thickness, a CoFe layer of 1.7 nm thickness, a Ru layer of 0.4 nm thickness, a CO2MnSi layer of 2.0 nm thickness, and a MgO layer of 4.0 nm thickness, in the same manner as described above. As depicted in
The inventors have also examined the relationships between an antiferromagnetic layer and nitride layers made of various kinds of nitrides. The tunnel-junction magnetoresistive film 45 was formed on the support substrate in the same manner as described above. It should be noted that CuN and Cu layers, TiN and Ti layers, NiCrN and NiCr layers, and CrN and Cr layers are employed as the underlayers in place of the aforementioned NiFeN and NiFe layers, respectively. The partial pressure of N2 gas was set at 73% to form the nitride layers such as the CuN layer, the TiN layer, the NiCrN layer and the CrN layer. In any case, the addition of nitrogen allows relocation of the oriented surface, as depicted in
The inventors have also examined the relationship between the partial pressure of nitrogen and the oriented surface of a nitride layer. The inventors formed a Ta layer of 3.0 nm thickness and a CuN layer of 10.0 nm thickness in sequence on a silicon substrate. Sputtering was employed to form the layers. Reactive sputtering was employed to form a nitride layer, namely the CuN layer, in the same manner as described above. The partial pressure was set at three levels such as 0%, 57% and 72%. As depicted in
It should be noted that a CoFe pinned layer of 1.5 nm thickness, a Ru80Rh20 (ruthenium rhodium alloy) nonmagnetic interlayer of 0.5 nm thickness and a Heusler alloy reference layer of 2.5 nm thickness may be employed in place of the aforementioned pinned layer 54, nonmagnetic interlayer 55 and reference layer 56 to establish a laminated ferri structure. In this case, the nonmagnetic interlayer preferably contains Rh in a range from 5 at % to 40 at %. More preferably, the nonmagnetic interlayer contains Rh in a range from 20 at % to 30 at %. The thickness of the nonmagnetic interlayer is preferably set in a range from 0.3 nm to 0.7 nm. More preferably, the thickness of the nonmagnetic interlayer is set in a range from 0.4 nm to 0.7 nm. It should be noted that the nonmagnetic interlayer may be a single Ru layer.
The inventors have also examined the efficiency of CO2FeAl0.5Si0.5 (hereinafter referred to as “CoFeAlSi”) employed in place of the aforementioned CO2MnSi. Formed in sequence on a glass substrate were a Ta layer of 3.0 nm thickness, a NiFeN layer of 3.0 nm thickness, an IrMn layer of 7.0 nm thickness, and a CoFeAlSi layer of 30.0 nm thickness, in the same manner as described above. A layered body was formed. Sputtering was employed to form each film. The sputtering was performed in the normal or room temperature. After the formation of the films, the layered body was subjected to heating process in a high vacuum oven at 350 degrees Celsius for duration of two hours. The inventors observed the crystalline structure of the layered body with an X-ray diffractometer. As depicted in
The inventors have also observed the magnetoresistance ratio (MR ratio). For the observation, formed in sequence on a glass substrate were a Ta layer of 3.0 nm thickness, a NiFe layer of 3.0 nm thickness, an IrMn layer of 7.0 nm thickness, a CoFeAlSi layer of 3.0 nm thickness, a MgO layer formed in an inclined film, and CoFeAlSi layer of 3.0 nm thickness, in the same manner as described above. The inclined film had a thickness constantly increasing from one end to the other end of a wafer. The thickness of the inclined film was set at 1.3 nm at the center of the wafer. A tunnel-junction magnetoresistive film according to a specific example was in this manner formed. Sputtering was employed to form each film. The sputtering was performed in the normal or room temperature. A layered body of the films was subjected to heating process in a high vacuum oven at 350 degrees Celsius for duration of two hours. The inventors made a tunnel-junction film according to a comparative example. CoFe layers each having 3.0 nm thickness were employed in the comparative example in place of the CoFeAlSi layers of the specific example, respectively. As is apparent from
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concept contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-088189 | Mar 2008 | JP | national |
| 2008-323983 | Dec 2008 | JP | national |
