Abstract:
The method and system for providing a perpendicular magnetic recording (PMR) head are described. The method and system include providing a metal underlayer and a PMR pole on the metal underlayer. The metal underlayer is amorphous. The PMR pole has a bottom and a top wider than the bottom. The PMR pole includes at least a first ferromagnetic layer, a second ferromagnetic layer, and a third ferromagnetic layer. The first ferromagnetic layer is antiferromagnetically coupled with the second ferromagnetic layer. The second ferromagnetic layer is antiferromagnetically coupled with the third ferromagnetic layer.

Description:
BACKGROUND 
       FIGS. 1 and 2  depict air-bearing surface (ABS) and side views, respectively, of a conventional perpendicular magnetic recording (PMR) head  10  used in recording a PMR media (not shown). The conventional PMR head  10  is typically used as a write head in a merged head including the conventional PMR head  10  and a read head. The conventional PMR head  10  includes a conventional first pole (P 1 )  12 , P 1  pad  13 , insulator  14 , a first coil  15 , a second pole (P 2 )  16 , a conventional PMR pole (main pole)  18 , insulator  20 , write gap  22 , a shield pad  24 , a second coil  26 , and shield  28 . The conventional PMR pole  18  has a height, h, and sidewalls that form an angle, θ, with the insulating layer  14 . Although not explicitly shown, seed layer(s) may be used in providing the conventional PMR pole  18 . In such a case, the conventional PMR pole  18  would reside on the seed layer. Although depicted as a single shield  28 , it is typically composed of two portions  28 A and  28 B that are formed separately. The PMR head  10  is also depicted with two coils  15  and  26 . However, PMR heads having a single coil may also be used. 
     In order to write data to a PMR media, the coils  15  and  26  are energized. Consequently, the PMR pole  18  is magnetized and the media written by flux from the pole tip  18 A. Based on the direction of current through the coils  16  and  28 , the direction of magnetic flux through the PMR pole  18  changes. Thus, bits having opposing magnetization can be written and the desired data stored on the PMR media. When the conventional PMR head  10  is not writing, no current is driven through the coils  15  and  26 . 
     The conventional PMR pole  18  may be plated or may be sputtered. A plated PMR pole  18  may suffer from a reduced magnetic moment. In addition, one of ordinary skill in the art will recognize that domain lockup, also termed remanent erasure, is an issue for plated PMR pole  18 . Domain lockup occurs when the conventional PMR head  10  inadvertently erases data in the PMR media even though no current energizes the PMR head  10 . This occurs due to a remanent field (a field/magnetization when there is zero current through the coils  15  and  26 ) remaining the PMR pole  18 . Stated differently, the PMR pole  18  may not completely demagnetize when in a quiescent (zero current) state. Further, the pole tip  18 A is sufficiently small that such deviations of the magnetization domains in the PMR pole  18  from a completely demagnetized state may produce significant magnetization in the pole tip  18 A. As a result, a high remanent field may be present in the PMR media even when no current is driven through the coils  15  and  26 . This remanent field may erase data recorded on the PMR media after the head  10  passes over the media for many revolutions. Because it involves this inadvertent erasure, domain lockup is undesirable. 
     Domain lockup may result not only in inadvertent erasure of data, but also failure of the PMR media. The servo areas (not shown) of the PMR media are usually written at much lower linear density than the areas that store user data. Consequently, the servo areas are more subject to being erased by the remanent field of the PMR head  10 . Erasure of servo areas may cause complete drive failure. Therefore, it would be highly desirable for domain lockup to be eliminated. 
     Sputtered conventional PMR poles  18  may provide some relief from the issues of plated PMR poles  18 . Sputtered, antiferromagnetically coupled magnetic layers may be used for the conventional PMR pole  18  in an attempt to reduce domain lockup. Because of the antiferromagnetic coupling, when in a quiescent state, the remanence magnetization of such a conventional PMR pole  18  is expected to be approximately zero. A zero remanence magnetization may be achieved along the hard axis of the PMR pole  18  using antiferromagnetic materials. However, in practice, a zero remanence magnetization may be difficult to achieve along the easy axis. Furthermore, the geometry around the pole tip  18 A is complex. As a result, the easy and hard axes may be switched if the combination of shape anisotropy and magnetoelastic anisotropy along the pole tip  18 A is larger than the induced anisotropy. Consequently, domain lockup may still be an issue for conventional PMR heads using sputtered antiferromagnetically coupled magnetic layers for the conventional PMR pole  18 . 
     Accordingly, what is needed is a system and method for providing a PMR head having reduced domain lockup. 
     SUMMARY 
     The method and system for providing a PMR head are disclosed. The method and system include providing a metal underlayer and a PMR pole on the metal underlayer. The metal underlayer is amorphous. The PMR pole has a bottom and a top wider than the bottom. The PMR pole includes at least a first ferromagnetic layer, a second ferromagnetic layer, and a third ferromagnetic layer. The first ferromagnetic layer is antiferromagnetically coupled with the second ferromagnetic layer. The second ferromagnetic layer is antiferromagnetically coupled with the third ferromagnetic layer. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  depicts an ABS view of a conventional PMR. 
         FIG. 2  depicts a side view of a conventional PMR. 
         FIG. 3  is an exemplary embodiment of a portion of a PMR head. 
         FIG. 4  is another exemplary embodiment of a portion of a PMR head. 
         FIG. 5  is an exemplary embodiment of a PMR head, as viewed from the ABS 
         FIG. 6  is an exemplary embodiment of a PMR head, as viewed from the side. 
         FIG. 7  is a flow chart depicting an exemplary embodiment of a method for forming a PMR head. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 3  is an exemplary embodiment of a portion of a PMR head  100 . The PMR head  100  is preferably used as a write head in a merged head including at least the PMR head  100  and a read head (not shown). The PMR head  100  includes an amorphous metal underlayer  110  and a PMR pole  120 . The PMR pole  120  includes magnetic layers  122 ,  126 , and  130  and nonmagnetic spacer layers  124  and  128 . The PMR head  100  is configured such that the PMR pole  120  has a reduced, and preferably substantially zero, remanence magnetization. Thus, the PMR pole  120  has a substantially zero remanence magnetization along both the easy and hard axes due to the use of antiferromagnetically coupled magnetic layers  122 ,  126 , and  130  and the amorphous underlayer  110 . In particular, the magnetic layers  122 ,  126 , and  130  within the antiferromagnetically coupled PMR pole  120  may be soft and the antiferromagnetic coupling between the layers  122 ,  126 , and  130  may be strong. For example, in one embodiment, the PMR pole  120  has a coercivity of less than fifty Oe. In a more preferred embodiment, the coercivity of the PMR pole  120  is less than twenty-five Oe. This is accomplished not only by configuring the layers  122 ,  124 ,  126 ,  128 , and  130 , but also through the use of the amorphous underlayer  110   
     Although the PMR pole  120  is shown as including three magnetic layers  122 ,  126 , and  130  and two spacer layers  124  and  128 , another number of magnetic layers and spacer layers may be used. Stated differently, analogous PMR poles (not shown) having a different number of antiferromagnetically coupled magnetic layers (not shown) on an amorphous underlayer (not shown) may be provided in accordance with the method and system in order to achieve similar benefits. For example,  FIG. 4  depicts another exemplary embodiment of a portion of a PMR head  100 ′ including an amorphous underlayer  110 ′ and a PMR pole  120 ′. The PMR head  100 ′ is analogous to the PMR head  100 . Consequently, analogous structures are labeled in a similar manner. 
     In a preferred embodiment, the magnetic moments of the magnetic layers  122 ,  126 , and  130  are configured such that when antiferromagnetically aligned, the net magnetic moment of the PMR pole  110  is zero. If material(s) having substantially the same magnetization are used, the thicknesses of the magnetic layers  122 ,  126 , and  130  are set to ensure that the PMR pole  110  has a zero net magnetic moment when the layers  122 ,  126 , and  130  antiferromagnetically aligned, as shown in  FIG. 3 . Consequently, for the PMR pole  110 , if the magnetizations of the layers  122 ,  126 , and  130  are the same, the thickness of the layer  126  is the same as the combined thicknesses of the layers  122  and  130 . Thus, if both of the layers  122  and  130  have a thickness, t, then the layer  126  has a thickness of 2 t. However, in other embodiments, other thickness combinations and/or magnetizations may be used. 
     The metal underlayer  110  has an amorphous crystal structure and is metallic. In a preferred embodiment, the amorphous metal underlayer  110  includes at least one metal having a high melting point. Examples of high melting point metals that may be used in the amorphous metal underlayer  110  include W, Nb, Mo, Zr, and/or Ta. Thus, the amorphous metal underlayer  110  may include at least one of W, Nb, Mo, Zr, and Ta. In another embodiment, the amorphous underlayer metal  110  includes at least one of NiNb, NiZr, NiZrNb, and an alloy that includes at least one of P and B. Use of the high melting point metal and/or an alloy that includes at least one of P and B allows the amorphous underlayer  110  to have an amorphous structure when deposited, for example via sputtering. The thickness of the amorphous underlayer  110  is not less than two hundred Angstroms and not more than three thousand Angstroms. In a preferred embodiment, the amorphous metal underlayer  110  has a thickness that is not less than five hundred Angstroms and not more than one thousand Angstroms. 
     In a preferred embodiment, the amorphous underlayer  110  has a lower surface roughness than a base layer that would normally underlie the seed layer for the PMR pole  120 . For example, such a base layer may have a surface roughness characterized by a root mean square on the order of fourteen Angstroms. In such a case, the surface roughness of the amorphous underlayer  110  may have a surface roughness characterized by a root mean square of not more than five Angstroms. However, in another embodiment, the surface roughness of the amorphous underlayer  110  may have a different relationship to the surface roughness of the base layer. 
     As discussed above, the PMR pole  120  preferably has a substantially zero remanence magnetization along both the easy and hard axes. It is believed that the reduced remanence magnetization may be attributed to a higher antiferromagnetic exchange coupling between the layers  122 ,  126 , and  130  and a smaller coercivity for the layers  122 ,  126 , and  130 . It is believed that the improvement in exchange coupling and reduction in coercivity are due, at least in part, to the amorphous underlayer  110 . In particular, it is believed that the reduced surface roughness provided by the amorphous underlayer  110  results in more consistent switching characteristics between the layers  122  and  130  as well as more uniform antiferromagnetic coupling between the layers  122  and  126  and the layers  126  and  130 . However, the method and system described herein do not depend upon a particular functional mechanism. 
     Thus, the PMR pole  120  may have a reduced remanence magnetization that is preferably to close to zero. Because of this reduced remanence magnetization, a PMR head  100  incorporating the PMR pole  120  and amorphous underlayer  110  may have reduced domain lockup. Consequently, performance may be improved. 
     The magnetic layers  122 ,  126 , and  130  each preferably has a high saturation magnetization and is magnetically soft. The magnetic layers  122 ,  126 , and  130  are also antiferromagnetically exchange coupled. The nonmagnetic spacer layers  124  and  128  are preferably thin and the magnetic layers  122 ,  126 , and  130  are strongly antiferromagnetically coupled. In addition, the spacer layers  124  and  126  are preferably metallic. In a preferred embodiment, for example, the spacer layers  124  and  128  each includes seven to nine Angstroms of Ru, and more preferably approximately eight Angstroms of Ru. Alternatively other materials such as Cr, Rh, and Cu may be used for the spacer layers  124  and  128 . 
     In addition to the layers  122 ′,  124 ′,  126 ′,  128 ′, and  130 ′, the PMR pole  120 ′ includes additional spacer layer  132  and additional magnetic layer  134 . The magnetic layer  134  is antiferromagnetically coupled with the layer  130 ′ and separated from the magnetic layer  130 ′ by the spacer layer  132 . The spacer layer  132  is analogous to the spacer layers  124 ′ and  128 ′. Thus, the spacer layer  132  is nonmagnetic, metallic, and preferably includes seven to nine Angstroms of Ru, and more preferably approximately eight Angstroms of Ru. 
     The net magnetic moment of the PMR pole  120 ′ is preferably substantially zero when the magnetic layers  122 ′,  126 ′,  130 ′, and  132  are antiferromagnetically aligned. Consequently, the net magnetic moments of the magnetic layers  122 ′ and  130 ′ are substantially the same as the net magnetic moments of the magnetic layers  126 ′ and  134 . If material(s) having substantially the same magnetization are used for the magnetic layers  122 ′,  126 ′,  130 ′ and  134 , then the sum of the thicknesses of the magnetic layers  122 ′ and  130 ′ are is substantially the same as the sum of the thicknesses of the magnetic layers  126 ′ and  134 . Thus, that the relative thicknesses of the magnetic layers  122 ′,  126 ′,  130 ′, and  134  may be different than for the magnetic layers  122 ,  126 , and  130 . However, the magnetic layers  122 ′,  126 ′,  130 ′, and  134  are still preferably configured to provide a substantially zero remanence magnetization. 
     The PMR pole  120 ′ functions in an analogous manner to the PMR pole  120 . Thus, the PMR pole  120 ′ has a substantially zero remanence magnetization along both the easy and hard axes. In particular, it is believed that the reduced surface roughness provided by the amorphous underlayer  110 ′ results in improved magnetic characteristics of the magnetic layers  122 ′,  126 ′,  130 ′, and  134  and, therefore, the reduced remanence of the PMR pole  120 ′. Because of this reduced remanence magnetization, a PMR head  100 ′ incorporating the PMR pole  120 ′ and amorphous underlayer  110 ′ may have reduced domain lockup. Consequently, performance may be improved. 
       FIGS. 5 and 6  depict an exemplary embodiment of a PMR head  200 , as viewed from the ABS and the side, respectively. The PMR head  200  is analogous to the PMR head  100 . The PMR head  200  is preferably used as a write head in a merged head including at least the PMR head  200  and a read head (not shown). The PMR head  200  includes a P 1   202 , P 1  pad  203 , insulator  204 , a first coil  205 , P 2   206 , an amorphous underlayer  210 , an antiferromagnetically coupled PMR pole  220  formed on the amorphous underlayer  210 , insulator  221 , write gap  222 , a shield pad  224 , a second coil  226 , and a top shield  228 . The top shield  228 , is typically composed of two portions  228 A and  228 B that are formed separately. Although the PMR head  200  is also depicted with two coils  205  and  226 , in another embodiment, a single coil may also be used. The PMR pole  220  also has a region  220 A proximate to the ABS. 
     The PMR pole  220  is analogous to the PMR pole  120 / 120 ′. In the embodiment shown, the PMR pole  220  sidewalls form an angle, θ, with the top surface of the amorphous underlayer  210 . Consequently, the PMR pole  220  includes antiferromagnetically coupled magnetic layers (not shown) analogous to the layers  122 / 122 ′,  126 / 126 ′,  130 / 130 ′, and  134 . The PMR pole  220  thus includes nonmagnetic metal spacer layers (not shown) analogous to the spacer layers  124 / 124 ′,  128 / 128 ′, and  132 , which alternate with and are sandwiched between the magnetic layers. For clarity, the antiferromagnetically coupled magnetic layers and nonmagnetic spacer layers are not explicitly shown. 
     The amorphous underlayer  210  is analogous to the amorphous underlayer  110 / 110 ′. As a result, the amorphous underlayer  210  has a surface roughness that is less than the surface roughness of the layer  204 , which can be considered to be a base layer for the PMR pole  220 . As a result, the PMR pole  220  has improved magnetic characteristics including a reduced magnetic layer coercivity and improved antiferromagnetic exchange coupling. Consequently, the remanence magnetization of the PMR pole  220  may be reduced, preferably to substantially zero. 
     Because the PMR pole  220  may have a reduced remanence magnetization, the PMR head  200  may have reduced domain lockup. Consequently, performance may be improved. 
       FIG. 7  is a flow chart depicting an exemplary embodiment of a method  300  for forming a PMR head  100 / 100 ′/ 200 . For simplicity, steps in the method  300  may be skipped or merged. For clarity, the method  300  is described in the context of the PMR head  200 . Referring to  FIGS. 5-7 , the method commences after the P 1   202  and other portions of the PMR head  200  have been provided. Thus, an underlying, or base, layer  204  is deposited, via step  302 . 
     The amorphous underlayer  210  is deposited, via step  304 . Step  304  may include depositing at least two hundred and not more than three thousand Angstroms, In a preferred embodiment, the thickness of the amorphous underlayer  210  is at least five hundred Angstroms and nor more than one thousand Angstroms. Step  304  may also include depositing a high melting point material, for example via sputtering. Step  304  may thus include depositing at least one of W, Nb, Mo, Zr, and/or Ta. In another embodiment, step  304  may include depositing at least one of NiNb, NiZr, NiZrNb, and an alloy that includes at least one of P and B. 
     The PMR pole  220  is provided on the amorphous underlayer  210 , via step  306 . Step  306  thus includes depositing the alternating magnetic layers and spacer layers such as the layers  122 / 122 ′,  124 / 124 ′,  126 / 126 ′,  128 / 128 ′,  130 / 130 ′,  132 , and  134  depicted in  FIGS. 3-4 . In addition, because these alternating magnetic and nonmagnetic spacer layers may be blanket deposited, step  306  may include providing a mask via photolithography and defining the PMR pole  220  utilizing the mask. 
     A pole trim may be performed, via step  308 . Step  308  may include, for example, performing ion milling at an angle. Consequently, the desired shape of the PMR pole  220  may be achieved. The amorphous underlayer  210  may be milled during the pole trim performed in step  308 . Because the amorphous underlayer  210  may be soft (quickly removed) with respect to the pole trim performed in step  310 , the amorphous underlayer  210  may also aid in shaping the PMR pole  220 . This advantage of using the amorphous underlayer  210  for the PMR pole  220  may be more clearly seen in  FIG. 5 . 
     Fabrication of the PMR head  200  is completed, via step  310 . Step  310  may thus include forming the insulating layer  221  around the PMR pole  220 , the write gap  222 , the pad  224 , the coil  226 , the top shield  228 , as well as performing other processes and/or forming other structures (not shown). Consequently, the PMR head  100 / 100 ′/ 200  may be fabricated and the benefits thereof achieved. 
     Thus, the PMR heads  100 ,  100 ′, and  200 , and preferably formed using the method  300  may have a zero remanence magnetization along both the easy and hard axes. As a result the PMR heads  100 ,  100 ′, and  200  may have reduced domain lockup. Furthermore, in at least some embodiments, the amorphous underlayer  110 / 110 ′/ 210  may also aid in shaping of the PMR pole  120 / 120 ′/ 220 . Consequently, the geometry and, therefore, performance of the PMR pole  120 / 120 ′/ 220  may be improved.