Abstract:
A thin film structure having a magnetic layer and a seed layer positioned adjacent to the magnetic layer is provided. The seed layer includes a L1 0  structure.

Description:
GOVERNMENT RIGHTS 
     This invention was made with United States Government support under Agreement No. 70NANB1H3056 awarded by the National Institute of Standards and Technology (NIST). The United States Government has certain rights in the invention. 
    
    
     BACKGROUND 
     Current storage systems include a multilayer structure having a substrate, an underlayer and a magnetic layer covered by an overcoat/lubrication layer. The magnetic layer is the layer on which information can be stored by altering a direction of magnetization of the magnetic layer. It is desirable to have a magnetic layer that exhibits high magnetic anisotropy with a limited amount of thermally stable grains. 
     To enhance the magnetic anisotropy of the magnetic layer, grains of the magnetic layer can be chemically ordered in an L1 0  structure. However, room temperature as-deposited magnetic layer unit cells are generally of face centered cubic structure. These face centered cubic materials have very low magnetic anisotropy. Under sufficient heat treatment or in situ high temperature deposition, the magnetic layer can develop a chemically ordered L1 0  structure that gives rise to high magnetic anisotropy. However, these processes can be expensive, time consuming, and not practical for a manufacturing process. 
     SUMMARY 
     A thin film structure having a magnetic layer and a seed layer positioned adjacent to the magnetic layer is provided. The seed layer includes a L1 0  structure. 
     Additionally, a magnetic recording medium is provided. The recording medium includes a substrate and an underlayer positioned above the substrate. A seed layer is positioned above the underlayer and has a L1 0  structure. A magnetic layer is positioned adjacent to the seed layer. 
     A method is also provided that includes providing a seed layer having an L1 0  structure. A magnetic layer having a L1 0  structure is provided on the seed layer. 
     Other features and benefits that characterize embodiments of the present invention will be apparent upon reading the following detailed description and review of the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a face centered cubic structure. 
         FIG. 2  is a schematic diagram of an L1 0  structure. 
         FIG. 3  is a schematic diagram of a thin film structure. 
         FIG. 4  is a schematic diagram of a thin film structure having two seedlayers. 
         FIG. 5  is a structure of a thin film structure having three seedlayers and two magnetic layers. 
         FIG. 6  is a flow chart of a method for forming a thin film structure. 
     
    
    
     DETAILED DESCRIPTION 
     A magnetic layer of a recording media can be comprised of a hard, magnetic metal alloy. For example, the magnetic alloy can be iron-platinum (FePt), cobalt-palladium (CoPd), iron-palladium (FePd) or cobalt-platinum (CoPt). The magnetic alloy can also be the above alloys with the third or more elemental dopant such as, Cu, Ni, Mn, Cr, etc. These alloys include two types of atoms that are present in chemical structures.  FIG. 1  is a schematic diagram of a face centered cubic structure  100 . In the face centered cubic structure  100  of  FIG. 1 , atoms of the magnetic alloy occupy lattice positions, for example lattice position  102 , of structure  100  randomly. For example, in the case of FePt, position  102  can either be occupied by an Fe atom or a Pt atom. 
     Magnetic materials such as FePt, FePd, CoPd and CoPt, usually exhibit a face centered cubic structure when deposited at room temperature. When in a face centered cubic structure, magnetic alloys have a low magnetic anisotropy. By chemically ordering structure  100 , a magnetic alloy can exhibit high magnetic anisotropy. A phase transformation needs to be induced in structure  100  to result in a chemically ordered structure. 
       FIG. 2  is a schematic diagram of a chemically ordered L1 0  structure  200  relative to axes  202 ,  204  and  206 . The L1 0  structure includes planes  208 ,  210  and  212  of atoms in which a first atom type in the structure occupies a first plane, a second atom type in the structure occupies a second, adjacent plane, and the first atom type occupies a third plane that is adjacent to the second plane. For example, plane  208  (defined by axes  204  and  206 ) is occupied by a first atom type in the illustrated specific positions (corners and a face center), which for example could be plantinum or palladium. Plane  210 , which is adjacent to plane  208 , is occupied by a second atom type in the illustrated specific positions (face centers), which for example can be iron, or cobalt. Plane  212 , which is adjacent to plane  210 , is again occupied by the first atom type. 
     Chemically ordered structures, such as the L1 0  structure  200 , are energetically preferred at room temperature. However, deposition of films are disordered unless otherwise ordered by a suitable phase transformation. To order the atoms in a L1 0  structure, enough diffusivity is needed during or after deposition. Thermal energy can be applied to the atoms to let them move around until the preferred energy position is found. Several different techniques for applying thermal energy during deposition can be used such as using an infrared carbon heater, an energy emitting lamp, resistance heater, etc. Under a phase transformation process, the L1 0  structure  200  is then obtained as in  FIG. 2 . 
     Within a thin film structure as used in magnetic recording media, a magnetic layer will more easily reach the L1 0  phase when an adjacent seedlayer includes an L1 0  structure. In this situation, the magnetic layer will experience a tensile stress caused by the seedlayer. To reduce the stress within the magnetic layer, the magnetic layer will shift to a tetragonal shape, which will induce its L1 0  phase transformation. A tetragonal shape includes a height, denoted as “c” in  FIG. 2 , that is less than a width, denoted as “a” in  FIG. 2 . In L1 0  FePt, “a” is equal to 0.3852 nm and “c” is equal to 0.3713 nm. The shift in shape to a tetragonal structure will expedite the magnetic layer L1 0  phase transformation and make it occur at a lower temperature. 
     Seedlayers that can be used to aid in this phase transformation include aluminum-titanium (AlTi), copper-titanium (CuTi), magnesium-indium (MgIn), plantinum-zinc (PtZn), copper-gold (CuAu), and cadmium-paladium (CdPd). One common feature of these alloys is a lower melting temperature than magnetic alloys discussed above, namely FePt, FePd, CoPd and CoPt. The lower melting temperature gives rise to higher diffusivity in the seedlayer over the magnetic layer. As a result, atoms of the seedlayer can move around more easily to reach the L1 0  phase. The L1 0  structure then aids in generating the L1 0  phase transformation of the magnetic layer. Lattice parameters of the L1 0  phase seedlayers discussed above are as follows: 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Lattice Parameters of Seedlayers 
               
             
          
           
               
                   
                   
                   
                   
                 Phase 
                   
                   
                   
               
               
                   
                   
                   
                   
                 transformation 
                   
                   
                 T melt   
               
               
                   
                   
                   
                   
                 temperature 
                 T melt   
                 T melt  element 
                 element 2 
               
               
                 Alloy 
                 a (nm) 
                 c (nm) 
                 c/a 
                 (° C.) 
                 alloy (° C.) 
                 1 (° C.) 
                 (° C.) 
               
               
                   
               
             
          
           
               
                 FePt 
                 3.853 
                 3.713 
                 0.96 
                 1300 
                 1580 
                 1536 
                 1772 
               
               
                 AlTi 
                 3.976 
                 4.049 
                 1.02 
                 1460 
                 1460 
                 660 
                 1670 
               
               
                 CuTi 
                 4.440 
                 2.856 
                 0.64 
                 982 
                 982 
                 1085 
                 1670 
               
               
                 MgIn 
                 4.571 
                 4.397 
                 0.96 
                 340 
                 400 
                 157 
                 649 
               
               
                 PtZn 
                 4.027 
                 3.474 
                 0.86 
                 &gt;900 
                 &gt;900 
                 1772 
                 420 
               
               
                 AuCu 
                 3.960 
                 3.670 
                 0.93 
                 385 
                 910 
                 1065 
                 1085 
               
               
                 CdPd 
                 4.277 
                 3.620 
                 0.85 
                 &gt;800 
                 &gt;800 
                 321 
                 1552 
               
               
                   
               
             
          
         
       
     
     Another feature of the above listed alloys is that there is very small or zero temperature gap between L1 0  phase transformation and melting. This indicates that when an alloy is formed from a liquid phase or vapor phase, the alloy will directly form into a L1 0  structure rather than form a face centered cubic or other structure. 
       FIG. 3  illustrates a thin film structure  300  that includes a substrate  302 , additional sub-layers  304 , underlayer  306 , seedlayer  308 , magnetic layer  310  and an overcoat/lubrication layer  312 . Substrate  302  forms a base of thin film structure  300  and can be made of any suitable material such as ceramic glass, amorphous glass or nickel-phosphorous (NiP) plated aluminum-magnesium (AlMg). Additional sub-layers  304  can include adhesion layers such as titanium (Ti), tantalum (Ta), and titanium chromium (TiCr) etc. as desired to serve as an interface between substrate  302  and underlayer  306 . Sub-layers  304  can also include heat sink layers that control the thermal properties of the whole media. Possible heat sink materials include copper (Cu), silver (Ag), gold (Au), aluminum (Al), tungsten (W), ruthenium (Ru), and their alloys among themselves or with other elements. 
     Underlayer  306  is optional and, if used, can comprise several layers. It is used to improve orientation distribution as well as enhance epitaxial growth (i.e. to form the same structure) of the seedlayer  308 . Some materials which can be used as an underlayer  306  include magnesium oxide (MgO), or an oxide with sodium chloride (NaCl) structure. etc. Metals and alloys of similar lattice parameter to the MgO can be used as second underlayer on top of MgO to further enhance the (100) orientation and the epitaxial growth between the underlayer and the L1 0  seedlayer. These metals can be chromium (Cr), nickel-aluminum (NiAl), ruthenium-aluminum (RuAl), etc. Underlayer  306  has a (100) orientation and seedlayer  308  is grown epitaxially in a (001) orientation on top of underlayer  306 . Additionally, seedlayer  308  can be grown together with oxides such as, MgO, silicon dioxide (SiO 2 ), titanium dioxide (TiO 2 ), tantalum oxide (Ta 2 O 5 ) or niobium oxide (Nb 2 O 5 ) to form granular structures. Magnetic layer  310  is grown on seedlayer  308  into a continuous or granular microstructure for patterned media and/or heat assisted magnetic recording (HAMR) media. Optionally, an overcoat/lubrication layer  312  can also be placed about the exterior surface of the magnetic recording media. 
       FIG. 4  further illustrates another thin film structure  400  that includes a substrate  402 , additional sub-layers  404 , underlayer  406 , first seedlayer,  408 , magnetic layer  410 , second seedlayer  412  and overcoat/lubrication layer  414 . In addition to structure  300  of  FIG. 3 , structure  400  includes two seedlayers, namely first seedlayer  408  and second seedlayer  412 . Magnetic layer  410  is placed between first seedlayer  408  and a second seedlayer  412  to enhance the L1 0  phase transformation of magnetic layer  410 . 
       FIG. 5  illustrates another exemplary thin film structure  500  that includes substrate  502 , additional sub-layers  504 , underlayer  506 , first seedlayer  508 , first magnetic layer  510 , second seedlayer  512 , second magnetic layer  514 , third seedlayer  516  and overcoat/lubrication layer  518 . In  FIG. 5 , there are three seedlayers  508 ,  512  and  516  and two magnetic layers  510  and  514 . The first magnetic layer  510  is between first seedlayer  508  and second seedlayer  512 . The second magnetic layer  514  is between the second seedlayer  512  and third seedlayer  516 . The two magnetic layers  510  and  514  aid in providing additional magnetic signal strength within the thin film structure  500  while seedlayers  508 ,  512  and  516  aid in inducing an L1 0  phase transformation in magnetic layers  510  and  514 . 
       FIG. 6  shows a process diagram of forming a magnetic recording media. A substrate, for example substrate  302 ,  402  or  502 , is provided at step  602 . Additional sub-layers can be provided adjacent to the substrate at step  604 . An underlayer can then be provided at step  606 . A seedlayer can then be deposited on the underlayer at step  608 . The underlayer can aid in epitaxial growth and orientation of the seedlayer. The seedlayer can undergo a phase transformation to a L1 0  structure during or after deposition. A magnetic layer is then grown or placed over the seedlayer in step  610 . For example, the magnetic layer can be FePt, CoPd, FePd or CoPt. An L1 0  phase transformation is induced at step  612 . The phase transformation can be a result of external thermal energy placed on the magnetic layer, which is also aided by the L1 0  structure of the seedlayer. 
     If desired, as illustrated by loop  614 , further seedlayers and/or magnetic layers can be added. For example, a further seedlayer can be placed adjacent to the magnetic layer. This seedlayer can aid in maintaining an L1 0  structure in the magnetic layer. If desired, a second magnetic layer can then be placed on top of the second seedlayer. Any number of seedlayers and/or magnetic layers can be used. 
     It is to be understood that even though numerous characteristics and advantages of various embodiments of the invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular application for the recording medium while maintaining substantially the same functionality without departing from the scope and spirit of the present invention. In addition, although the embodiment described herein is directed to a thin film structure, it will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other magnetic recording materials without departing from the scope and spirit of the present invention.