Patent Publication Number: US-2009237835-A1

Title: Switching field controlled (SFC) media using anti-ferromagnetic thin layer in magnetic recording

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject matter disclosed generally relates to disk media of hard disk drives. 
     2. Background Information 
     Hard disk drives contain a plurality of heads that are magnetically coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. 
     There are generally two different types of magnetic heads, horizontal recording heads and perpendicular recording heads (“PMR heads”). Horizontal recording heads magnetize the disk in a direction that is essentially parallel with the outer surface of the disk. PMR heads magnetize the disk in a direction essentially perpendicular to the outer surface of the disk. PMR heads are preferred because perpendicular recording allows for higher bit densities and corresponding increases in the data capacity of the drive. 
     The areal density of perpendicular recording is limited by magnetic cross-talk between adjacent areas of the disks. One approach to limiting cross-talk is to create a disk composed of a plurality of magnetic dots that are separated by non-magnetic material. The non-magnetic material inhibits magnetic cross-talk between the magnetic dots. Such disks are commonly referred to as bit patterned media. 
     When writing on a bit patterned media the recording head must switch polarity while the write element of the head is adjacent to the magnetic dot. If the polarity is not switch during a critical window the dot is not re-magnetized and data is not properly written to disk. Consequently, bit patterned media have stringent writing requirements. 
     BRIEF SUMMARY OF THE INVENTION 
     A patterned disk for a hard disk drive. The patterned disk includes an anti-ferromagnetic layer of Fe x Ni 1-x O over a substrate. The disk also includes a magnetic layer that is adjacent to the anti-ferromagnetic layer of Fe x Ni 1-x O, and is formed into a plurality of dots separated by a non-magnetic material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a hard disk drive; 
         FIG. 2  is an illustration of a cross-section of a disk of the hard disk drive; 
         FIGS. 3   a - c  are illustrations showing the spin configurations within a magnetic material and an adjacent anti-ferromagnetic layer of Fe x Ni 1-x O exposed to different levels of an external magnetic field H; 
         FIG. 4  is an enlarged top view of the disk showing a plurality of magnetic dots. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed is a patterned disk for a hard disk drive. The patterned disk includes an anti-ferromagnetic layer of Fe x Ni 1-x O over a substrate. The disk also includes a magnetic layer that is adjacent to the anti-ferromagnetic layer of Fe x Ni 1-x O, and is formed into a plurality of dots separated by a non-magnetic material. The anti-ferro-magnetic layer of Fe x Ni 1-x O with the magnetic layer create an exchange-spring system that has a relatively low switching field. The anti-ferromagnetic layer of Fe x Ni 1-x O has a Neel temperature that maintains thermal stability. The low switching field improves reliability when the disk is a bit pattern media used in perpendicular recording. 
     Referring to the drawings more particularly by reference numbers,  FIG. 1  shows an embodiment of a hard disk drive  10 . The disk drive  10  may include one or more magnetic disks  12  that are rotated by a spindle motor  14 . The spindle motor  14  may be mounted to a base plate  16 . The disk drive  10  may further have a cover  18  that encloses the disks  12 . 
     The disk drive  10  may include a plurality of heads  20  located adjacent to the disks  12 . The heads  20  may have separate write and read elements (not shown) that magnetize and sense the magnetic fields of the disks  12 . 
     Each head  20  may be gimbal mounted to a flexure arm  22  as part of a head gimbal assembly (HGA). The flexure arms  22  are attached to an actuator arm  24  that is pivotally mounted to the base plate  16  by a bearing assembly  26 . A voice coil  28  is attached to the actuator arm  24 . The voice coil  28  is coupled to a magnet assembly  30  to create a voice coil motor (VCM)  32 . Providing a current to the voice coil  28  will create a torque that swings the actuator arm  24  and moves the heads  20  across the disks  12 . 
     Each head  20  has an air bearing surface (not shown) that cooperates with an air flow created by the rotating disks  12  to generate an air bearing. The air bearing separates the head  20  from the disk surface to minimize contact and wear. 
     The hard disk drive  10  may include a printed circuit board assembly  34  that includes a plurality of integrated circuits  36  coupled to a printed circuit board  38 . The printed circuit board  38  is coupled to the voice coil  28 , heads  20  and spindle motor  14  by wires (not shown). 
       FIG. 2  shows an embodiment of the disk  12 . The disk  12  includes a substrate  50  that supports an underlayer  52 . The underlayer  52  may include an adhesion layer, an AFC layer, a blocking layer and an intermediate layer as is known in the art. The disk  12  includes a magnetic layer  54  and a protective layer  56 . The protective layer  56  may include carbon-like material as is known in the art. 
     The disk  12  further includes an anti-ferromagnetic layer of Fe x Ni 1-x O  58 . As shown in  FIGS. 3   a - c , the combination of the magnetic layer and anti-ferromagnetic layer  58  creates a spring-exchange system that lower the coercivity and corresponding switching field of the media. 
     As shown in  FIG. 3   a , when the external field is zero, the magnetic material is magnetized in a certain direction and the Fe x Ni 1-x O layer is not magnetized.  FIG. 3   b  shows the application of an external field in a polarity opposite from the polarity at which the magnetic layer is magnetized and at an amplitude below a threshold H S . The Fe x Ni 1-x O layer becomes magnetized in the direction of the external field H. The direction of magnetization in the magnetic field remains in an opposite direction. As shown in  FIG. 3   c , both layers  54  and  58  become magnetized in the direction of the magnetic field when the external magnetic field H exceeds the threshold H S . 
     When used with a perpendicular recording head the low switching field increases the switching window in which the head can re-magnetize the disk. This relaxes the timing requirements of writing data onto the disk. The Fe x Ni 1-x O material has a Neel temperature between 200° to 520° K and thus will maintain the para-magnetic characteristics shown in  FIGS. 3   a - c , even at temperatures below ambient. 
     As shown in  FIG. 4 , the magnetic layer  54  is arranged into a plurality of dots  60  that are separated by non-magnetic material  62  such as air. The non-magnetic material inhibits magnetic cross-talk between the magnetic dots  62 . 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.