Abstract:
A magnetic head comprising a first layer containing NiFe having a concentration of iron that is at least thirty percent and not more than seventy percent; a second layer that adjoins the first layer and contains FeCoN having a concentration of iron that is greater than the second layer&#39;s concentration of cobalt, having a concentration of nitrogen that is less than the second layer&#39;s concentration of cobalt and less than three percent; and a third layer containing FeCoNi having a concentration of nickel that is less than eight percent, having a concentration of cobalt that is less than the third layer&#39;s concentration of iron and greater than the third layer&#39;s concentration of nickel, the third layer adjoining only one of the first and second layers. The first and second layers may be repeated to form a magnetically soft high B S  laminate for a pole layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit under 35 U.S.C. 120 (is a continuation-in-part) of U.S. patent application Ser. No. 10/137,030, filed May 1, 2002, now U.S. Pat. No. 6,778,358 which is incorporated by reference herein. Also incorporated by reference is the concurrently filed application by the same inventors, entitled: MAGNETICALLY SOFT, HIGH SATURATION MAGNETIZATION LAMINATE OF IRON-COBALT-NITROGEN AND IRON-NICKEL FOR PERPENDICULAR MEDIA UNDERLAYERS. 
    
    
     TECHNICAL FIELD 
     The present invention relates to magnetic devices, for example electromagnetic transducers such as magnetic heads of disk or tape drives. 
     BACKGROUND 
     Electromagnetic transducers such as heads for disk or tape drives commonly include Permalloy (approximately Ni 0.81 Fe 0.19 ), which is formed in thin layers to create magnetic features. Permalloy is known to be magnetically “soft,” that is, to have high permeability and low coercivity, allowing structures made of Permalloy to act like good conductors of magnetic flux. For example, an inductive head may have conductive coils that induce magnetic flux in an adjacent Permalloy core, that flux employed to magnetize a portion or bit of an adjacent media. That same inductive head may read signals from the media by bringing the core near the magnetized media portion so that the flux from the media portion induces a flux in the core, the changing flux in the core inducing an electric current in the coils. Alternatively, instead of inductively sensing media fields, magnetoresistive (MR) sensors or merged heads that include MR or giant magnetoresistive (GMR) sensors may use thinner layers of Permalloy to read signals, by sensing a change in electrical resistance of the sensor that is caused by the magnetic signal. 
     In order to store more information in smaller spaces, transducer elements have decreased in size for many years. One difficulty with this deceased size is that the amount of flux that needs to be transmitted may saturate elements such as magnetic pole layers, which becomes particularly troublesome when ends of the pole layers closest to the media, commonly termed pole tips, are saturated. Magnetic saturation in this case limits the amount of flux that is transmitted through the pole tips, limiting writing or reading of signals. Moreover, such saturation may blur that writing or reading, as the flux may be evenly dispersed over an entire pole tip instead of being focused in a corner that has relatively high flux density. For these reasons the use of high magnetic saturation materials (also known as high moment or high B S  materials) in magnetic core elements has been known for many years. 
     For instance, iron is known to have a higher magnetic moment than nickel, so increasing the proportion of iron compared to nickel generally yields a higher moment alloy. Iron, however, is also more corrosive than nickel, which imposes a limit to the concentration of iron that is feasible for many applications. Also, it is difficult to achieve soft magnetic properties for primarily-iron NiFe compared to primarily-nickel NiFe. Anderson et al., in U.S. Pat. No. 4,589,042, teach the use of high moment Ni 0.45 Fe 0.55  for pole tips. Anderson et al. do not use Ni 0.45 Fe 0.55  throughout the core due to problems with permeability of that material, which Anderson et al. suggest is due to relatively high magnetostriction of Ni 0.45 Fe 0.55 . 
     As noted in U.S. Pat. No. 5,606,478 to Chen et al., the use of high moment materials has also been proposed for layers of magnetic cores located closest to a gap region separating the cores. Also noted by Chen et al. are some of the difficulties presented by these high moment materials, including challenges in forming desired elements and corrosion of the elements once formed. Chen et al. state that magnetostriction is another problem with Ni 0.45 Fe 0.55 , and teach the importance of constructing of heads having Permalloy material layers that counteract the effects of that magnetostriction. This balancing of positive and negative magnetostriction with plural NiFe alloys is also described in U.S. Pat. No. 5,874,010 to Tao et al. 
     Primarily iron FeCo alloys are known to have a very high saturation magnetization but also high magnetostriction that makes them unsuitable for many head applications. That is, mechanical stress during slider fabrication or use may perturb desirable magnetic domain patterns of the head.  FIG. 8  shows a B/H loop  12  of a FeCoN layer that was formed by sputtering deposition at room temperature, the layer having a thickness of approximately 500 Å and having a composition of approximately Fe 0.66 Co 0.28 N 0.06 . The applied H-field is shown in oersted (Oe) across the horizontal axis while the magnetization of the layer is plotted in normalized units along the vertical axis, with unity defined as the saturation magnetization for a given material. The FeCoN layer has a saturation magnetization (B S ) of approximately 24.0 kilogauss and is magnetically isotropic, as shown by the single B/H loop  12 . B/H loop  12  also indicates a relatively high coercivity of about 80 oersted, which may be unsuitable for applications requiring soft magnetic properties. 
     In an article entitled “Microstructures and Soft Magnetic Properties of High Saturation Magnetization Fe—Co—N alloy Thin Films,” Materials Research Society, Spring meeting, Section F, April 2000, N. X. Sun et al. report the formation of FeCoN films having high magnetic saturation but also high magnetostriction and moderate coercivity. Sun et al. also report the formation of a thin film structure in which FeCoN is grown on and capped by Permalloy, to create a sandwich structure having reduced coercivity but compressive stress. The magnetostriction of this sandwich structure, while somewhat less than that of the single film of FeCoN, may still be problematic for head applications. 
     SUMMARY 
     In one embodiment, a magnetic head is disclosed, comprising a first layer containing NiFe having an atomic concentration of iron that is at least thirty percent and not more than seventy percent; a second layer that adjoins the first layer and contains FeCoN having an atomic concentration of iron that is greater than the second layer&#39;s atomic concentration of cobalt, having an atomic concentration of nitrogen that is less than the second layer&#39;s atomic concentration of cobalt and less than three percent; and a third layer containing FeCoNi having an atomic concentration of nickel that is less than eight percent, having an atomic concentration of cobalt that is less than the third layer&#39;s atomic concentration of iron and greater than the third layer&#39;s atomic concentration of nickel, the third layer adjoining only one of the first and second layers. 
     The magnetic head may include a first plurality of layers each containing NiFe having an atomic concentration of iron that is at least about thirty percent; a second plurality of layers that is interleaved with the first plurality of layers, the second plurality of layers each containing FeCoN having an atomic concentration of iron that is greater than an atomic concentration of cobalt, and having an atomic concentration of nitrogen that is less than the atomic concentration of cobalt, the atomic concentration of nitrogen being less than eight percent; and a layer containing FeCoNi that adjoins one of the layers containing NiFe or one of the layers containing FeCoN. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cutaway cross-sectional view of a sandwich structure made of a primarily iron FeCoN layer affixed between a pair of FeNi layers. 
         FIG. 2  is a cutaway cross-sectional view of a laminated structure made of a plurality of primarily iron FeCoN layers interleaved with a plurality of primarily iron FeNi layers. 
         FIG. 3  is plot of a B/H loop of the laminated structure of  FIG. 2 . 
         FIG. 4  is a plot of saturation magnetization as a function of nitrogen gas content for (Fe 0.70 Co 0.30 )N. 
         FIG. 5  is a cutaway cross-sectional view of a perpendicular recording transducer including the laminated structure of  FIG. 2 , in close proximity to a medium including a soft magnetic underlayer that may be formed of a similar laminate. 
         FIG. 6  is a cutaway cross-sectional view of a merged MR and longitudinal inductive transducer including a trailing pole layer electroplated atop a cap layer for the laminate of  FIG. 2 . 
         FIG. 7  is a cutaway cross-sectional view of the transducer of  FIG. 6  disposed in close proximity to a medium. 
         FIG. 8  is plot of a B/H loop of a prior art FeCoN layer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a cutaway cross-sectional view of a sandwich structure  20  made of an iron-cobalt-nitride (FeCoN) layer  22  affixed between a pair of iron—nickel (FeNi) layers  24  and  26 . The sandwich structure  20  is formed on a substrate  28  that provides a smooth surface promoting favorable crystallographic growth of layers  22 ,  24  and  26 . The FeCoN layer  22  has a thickness of approximately 475 Å and has a composition of approximately Fe 0.69 Co 0.30 N 0.01 . The FeNi layers  24  and  26  each have a thickness of approximately 25 Å and have a composition of approximately Ni 0.55 Fe 0.45 . Layers  22 ,  24  and  26  were formed by DC magnetron sputtering deposition at room temperature. Magnetron sputtering has a deposition rate that is approximately ten times faster than that of RF sputtering, which is an advantage in commercial applications such as magnetic head production. The substrate may be a silicon dioxide, alumina, chromium, tantalum or titanium, for example. 
       FIG. 2  is a cutaway cross-sectional view of a laminated structure  40  made of a plurality of primarily iron FeCoN layers  42  interleaved with a plurality of primarily iron FeNi layers  44 . The sandwich structure  20  is formed on a substrate  46  that provides a surface promoting favorable microstructural growth of layers  42  and  44 . The FeCoN layers  42  each have a thickness of approximately 475 Å and a composition of approximately Fe 0.69 Co 0.30 N 0.01 . The FeNi layers  42  each have a thickness of approximately 25 Å and have a composition of approximately Ni 0.55 Fe 0.45 . Layers  42  and  44  were formed by magnetron sputtering deposition on substrate  46  at room temperature. Various other compositions and thicknesses may also be suitable. For example, the FeCoN layers may have atomic concentrations of iron in a range between 50% and 80%, atomic concentrations of cobalt in a range between 17% and 50%, and atomic concentrations of nitrogen in a range between 0.01% and 3%. As another example, the NiFe layers may have atomic concentrations of iron in a range between 30% and 70%, and atomic concentrations of nickel in a range between 70% and 30%. The thickness of any of the layers may for example be in a range between a few angstroms and one hundred nanometers. 
       FIG. 3  shows B/H loops  30  and  33  for the laminated structure  40  of  FIG. 2  having an overall thickness of about 2500 Å. The laminated structure has a saturation magnetization (B S ) of approximately 2.4 tesla (T), nearly that of the single layer of FeCoN. The coercivity of the hard axis, which is defined as the applied field of the loop  30  at which the magnetization is zero, is about 4 oersted (Oe) while the coercivity of the easy axis is about 12 Oe as shown by loop  33 . The permeability is approximately 2000, and the laminate has been found to be suitable for applications such as pole layers for magnetic heads. 
       FIG. 4  is a plot  60  of experimentally determined saturation magnetization B S  of FeCoN for various concentrations of nitrogen gas, normalized for zero nitrogen. The plot  60  was generated using a sputtering target of Fe 0.70 Co 0.30  and varying the amount of nitrogen gas. The concentration of nitrogen in the solid layer of FeCoN has been found to be about the same as that in the gas. At the wafer level, the concentration of various elements can be determined by Auger Electron Spectroscopy (AES) or Electron Energy Loss Spectroscopy (EELS), while concentrations of various elements of a layer in a device such as a magnetic head can be determined by Transmission Electron Microscopy (TEM). The plot  60  has a peak saturation magnetization B S  at about 1% nitrogen, with B S  generally declining as the nitrogen content is increased above 1%. The coercivity generally increases as the nitrogen content of FeCoN layers declines from approximately 7%, however, arguing against the use of low nitrogen content FeCoN in magnetic heads. We have found that a coercivity as high as 30 Oe can be tolerated for high B S  applications such as pole layers of magnetic heads, and so the nitrogen content of FeCoN layers for such high B S  applications in which the FeCoN is interleaved with NiFe has been selected to be less than about 3%. A laminated structure having lower coercivity may be desirable for other applications such as soft magnetic underlayers for disks, in which having such a high B S  may not be as critical as for pole tips. 
     The magnetically soft, high B S  laminate  40  is well suited for use in a write pole tip for perpendicular recording. In this case, a laminated write pole layer may be formed entirely of alternating layers of FeCoN and NiFe having an overall thickness of about 3000 Å or less. The laminated write pole layer may be trimmed to have a trapezoidal cross-section, including a trapezoidal write pole tip. The laminated write pole layer does not appear to suffer from excessive magnetostriction, perhaps because it is encapsulated in other solid materials. 
       FIG. 5  is a cutaway cross-sectional view of a portion of a disk drive including a magnetic head  100  designed for perpendicular recording on a relatively moving medium  150 . The head  100  includes a write pole layer  101  formed of interleaved layers of FeCoN and NiFe similar to that described above, formed to an overall thickness of about 2500 Å. The medium  150  includes a substrate  152  over which a soft magnetic underlayer  155  has been formed. The underlayer  155  may also be formed of interleaved layers of FeCoN and NiFe similar to that described above, although the atomic concentration of nitrogen in the FeCoN layers may be about 5%, instead of about 1% for the write pole  101 . The underlayer may be thinner than is conventional for perpendicular media, for example, less than 500 nanometers, due to the relatively high B S  of over 2.3 T. 
     A media layer  158  is disposed over the underlayer  155 , the media layer having an easy axis of magnetization that is substantially perpendicular to a major surface  153  of the medium. A thin, physically hard overcoat  156  separates the media layer  158  from the medium surface  153 . The medium  150 , which may for example be a rigid disk, is moving relative to the head in a direction shown by arrow  159 . The head  100  may be spaced from the medium  150  by a nanoscale air bearing, or the head may be in frequent or continuous contact with the medium during operation. The word nanoscale as used herein is meant to represent a size that is most conveniently described in terms of nanometers, e.g., between about one nanometer and about two hundred nanometers. 
     The head  100  has a medium-facing surface  166  disposed adjacent to the disk. The laminated write pole layer  101  terminates adjacent to the medium-facing surface in a first pole tip  170 , which may sometimes be called a write pole tip. A soft magnetic layer  188  adjoins the write pole layer  101  but terminates further from the medium-facing surface  166  than the first pole tip  170 , layers  101  and  188  combining to form a write pole. Another soft magnetic layer  178  is magnetically coupled to the write pole layer  101  in a region that is removed from the medium-facing surface and not shown in this figure, and is magnetically coupled to the write pole layer  101  adjacent to the medium-facing surface by a soft magnetic pedestal  175 . The soft magnetic layer  178  and pedestal  175  may be considered to form a return pole layer that terminates adjacent to the medium-facing surface in a second pole tip  180 . At least one electrically conductive coil section may be disposed between layers  101  and  178  and another coil section disposed upstream of layer  188 , to induce magnetic flux in the pole layers. 
     Although not apparent in this view, the return pole tip  180  may have an area that is at least two or three orders of magnitude greater than that of the write pole tip  170 . Alternatively, another return pole layer and return pole tip may additionally be provided, for example between the write pole layer and a MR sensor. The write pole tip  170  may have a substantially trapezoidal shape that has a maximum track width at a trailing corner  171 . The trailing corner  171  of the write pole tip  170  may be approximately equidistant from soft magnetic underlayer  155  and soft magnetic pedestal  175  in this embodiment. The write pole layer  170  may have a B S  that is between about 2.35T and 2.45T, while the soft magnetic pedestal  175  may have a B S  that is substantially less, e.g., less than 2.0T. 
       FIG. 6  is a cutaway cross-sectional view of a magnetic head  200  that can be used for longitudinal recording and which includes laminated high B S  FeCoN/NiFe pole layers. As described below, the head  200  includes a merged magnetoresistive (MR) and inductive transducer, although the laminated high B S  FeCoN/NiFe pole layers may instead be used for example in a separate inductive transducer, such as in a piggyback head, or in other applications in which magnetically soft, high B S  materials are desirable. 
     The head  200  is formed on a wafer substrate  241 , which may contain Al 2 O 3 , AlTiC, Si, SiC or other conventional materials. A first magnetically soft shield layer  242  is disposed atop the substrate  241 . A first read gap layer  244  composed of electrically insulating, nonmagnetic material such as Al 2 O 3  is disposed on shield layer  242 . A MR sensor  246  is disposed atop the first read gap layer  244 , and a second read gap layer  248  composed of electrically insulating, nonmagnetic material such as Al 2 O 3  is disposed on the MR sensor. The MR sensor  246  may include a single layer of anisotropic magnetoresistive (AMR) material such as Permalloy, or the sensor may contain plural or multiple layers of sensor materials as is known to form a spin-valve sensor, giant magnetoresistive (GMR) sensor, dual stripe magnetoresistive (DSMR) sensor or other known types of sensing mechanisms. In other embodiments, such a MR sensor may be configured for current-perpendicular-to-plane (CPP) operation involving, for example, spin-dependent tunneling (SDT) or spin-valve sensors. The MR sensor  246  may be trimmed to leave an insulating layer  249  formed of a dielectric such as Al 2 O 3  distal to a media-facing surface  270 . 
     A second magnetically soft shield layer  250  is disposed atop the second read gap layer  248 , the second shield layer also serving in this merged transducer as a first write pole layer  250 . In an alternative embodiment, a first write pole is separated from the second shield layer. The layer  250  may be formed of an electroplated layer  235  of Permalloy or other materials having higher saturation magnetization, including magnetically soft, primarily-iron NiFe or FeXN, where X is an element such as Ta, Rh, Al, etc., or FeCoNi. Layer  235  may be electroplated and then polished to form a smooth surface, upon which a first laminated FeCoN/FeNi structure  251  can be formed. The laminated structure  251  includes layers of primarily-iron FeCoN interleaved with layers of FeNi, and provides a magnetically soft high moment material upon which a submicron nonferromagnetic gap layer  252  is formed. The gap layer  252  separates the first write pole  250  from a second write pole layer  260 , and magnetic flux communicated between the pole layers  250  and  260  can fringe out from the gap layer to write magnetic pattern on an adjacent media. 
     A second laminated FeCoN/FeNi structure  262  is formed on the gap layer  252 . The laminated structure  162  includes layers of primarily-iron FeCoN interleaved with layers of primarily-iron FeNi, and provides a second magnetically soft high moment layer adjoining the nonferromagnetic gap layer  152 . Having the laminated FeCoN/FeNi structure  262  adjoining a trailing edge of the gap layer  252  allows sharply defined, high density magnetic patterns to be written onto an adjacent media. Materials from which gap layer  252  can be made include dielectric materials such as Al 2 O 3  or SiO 2  or metals such as chromium, tantalum or nickel-niobium. The gap layer  252  can serve as a seed layer promoting favorable deposition of the laminated FeCoN/FeNi structure  262 . The laminated FeCoN/FeNi structure  262  does not appear to suffer from excessive magnetostriction, perhaps because it is encapsulated in other solid materials. 
     An electrically conductive coil  255  is provided atop an insulating layer  257  to induce magnetic flux in the pole layers  250  and  260  for writing signals to a medium. The coil  255  is encircled by baked photoresist  254  that provides insulation between coil sections and also provides a sloped surface that allows the pole layers  250  and  260  to be separated by several microns adjacent the coil  255  and less than two hundred nanometers adjacent the media-facing surface  270 . In another embodiment, a second pole layer can be substantially flat, with the magnetic core brought close to the gap by an additional magnetic layer, which may be termed a pedestal, adjoining either or both of the pole layers. In yet another embodiment, such a pedestal can be formed adjoining a second pole layer that curves in a similar fashion as pole layer  260 , with the pedestal and pole layer stitched together adjacent to the media-facing surface  270 . In any of these embodiments, the write pole tip adjoining the trailing portion of the gap can be made of laminated FeCoN, and may have a track-width dimension of less than 200 nm. 
     The second laminated FeCoN/FeNi structure  262  is formed in a plurality of DC magnetron sputtered layers, beginning with NiFe having an atomic concentration of both nickel and iron in a range between about 30% and 70%, which may be formed to a thickness of 20 Å–30 Å. Alternatively, for the situation in which the gap layer  252  is made of Cr or NiNb, the initial layer of the laminated FeCoN/FeNi structure  262  may be formed of primarily-iron FeCoN. After formation of at least three layers of the primarily-iron FeCoN interleaved with at least three layers of the FeNi, a cap layer  282  of FeCoNi may be formed by RF sputtering atop the laminated structure  262 . A layer  266  of FeCoNi having atomic concentrations of elements that are substantially identical to that of the cap layer  282  may then be formed by electroplating. The cap layer  282  may be denser and less subject to corrosion than the than the laminated FeCoN/FeNi structure  262  of CoNiFe, particularly in a sloped region  288  of the pole layer  260 , where the laminated structure  282  may be more porous and defect prone. Having a cap layer formed of a similar concentration of metals as the electroplating solution may also help to avoid chemical reactions that may otherwise remove parts of the laminated structure  282 . 
     Alternatively, pole layer  260  may be formed entirely of a magnetically soft laminated FeCoN/FeNi structure having high saturation magnetization, which may be feasible due to the relatively high deposition rate of magnetron sputtering, so that for example a laminated structure a few microns in thickness can be formed in less than one hour. 
     After formation of second pole layer  260 , that layer may be masked and trimmed by a directional etching process such as ion beam etching (IBE) to define a trailing pole tip. The etching may be designed to also cut into the first pole layer  250 , creating a leading pole tip that is aligned with the trailing pole tip. A protective coating layer  268  of Al 2 O 3 , diamond like carbon (DLC) or other hard materials is then formed on what will become a trailing end  275  of the head, after which the wafer substrate  241  and transducer layers are diced into thousands of heads. A protective coating  272  has also been formed on the media-facing surface  270  of the transducer. The media-facing surface  270  is formed along one die edge. Note that the MR sensor  246  may alternatively be formed after the formation of the inductive core that includes write poles  250  and  260 , affording higher temperature processing of the write poles. In an alternative embodiment, sensing is performed inductively with the same transducer elements that are used to write magnetic patterns on the media, without the need for a MR sensor. 
       FIG. 7  shows the merged transducer  200  disposed in close proximity to a medium  202  which is moving relative to the head as shown by arrow  212 , from a leading end to the trailing end  275  of the head. The media  200  may be a disk or tape, for example, which includes a media layer or layers  205  disposed atop a substrate  208 , with an overcoat layer  210  protecting the media layer  205 . The write poles  250  and  260  form a magnetic circuit or loop to encourage the flow of magnetic flux across the write gap layer  252 . An electrical current flowed through the coil  255  induces a magnetic flux in the write layers that fringes out from the nonferromagnetic gap layer  252  to write a magnetic bit in the media layer  205 . The MR sensor  246  can read magnetic bits that have been written on the media. 
     Although the present disclosure has focused on teaching the preferred embodiments, other embodiments and modifications of this invention will be apparent to persons of ordinary skill in the art in view of these teachings. For example, the primarily-iron laminates of FeCoN/FeNi can be employed in various devices that benefit from high saturation magnetization, magnetically soft materials, such as magnetic sensors, magnetic force microscopes, magnetic switches, etc. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.