Abstract:
A magnetic shielding element for a magnetic recording and sensing device which prevents the problem of pop-corn noise or covariance of amplitude noise in the magnetic sensing device. The shielding element has a layer of antiferromagnetic exchange material formed on a layer of single domain first ferromagnetic material. The single domain first ferromagnetic material is stabilized by the antiferromagnetic exchange material. A layer of non-magnetic metal is then formed on the layer of antiferromagnetic exchange material and a layer of second ferromagnetic material is formed on the layer of non-magnetic metal to complete the shielding element. When the single domains of the first ferromagnetic material are disturbed by the strong magnetic fields of a write cycle they relax with a relaxation time of pico seconds and are fully relaxed before a read cycle begins. The fully relaxed layer of first ferromagnetic material then shields the magnetic sensing device from magnetic field fluctuations caused by the slower relaxation of the domains in the layer of second ferromagnetic material during a read cycle.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to magnetic shielding of a magnetic sensing device and more particularly to a magnetic shield using a layer of single domain ferromagnetic material, formed on a layer of antiferromagnetic exchange material to stabilize the single domain nature of the ferromagnetic material, as a key part of the shield. 
     (2) Description of the Related Art 
     One of the major challenges of magnetic recording and sensing devices, such as those devices using spin valve, anisotropic magnetoresistive, spin dependent tunneling magnetic sensor devices is the amplitude stability of the sense current after write excitation. The strong field used for write excitation can rearrange the domain patterns of the shields shielding the magnetic sensor device. After the writing cycle has been completed the domains in the shield will relax to their final domain state, Since these shields are magnetically coupled to the magnetic sensor device, this relaxation of the domains to the final domain state will cause noise, such as pop-corn noise and covariance of amplitude noise, in the sense current. 
     U.S. Pat. No. 5,898,548 to Dill et al. describes a magnetic recording system with a magnetic tunnel junction magnetoresistive read head located between two spaced-apart magnetic shields. Electrically conductive spacer layers are located at the top and bottom of the magnetic tunnel junction device and connect the magnetic tunnel junction device to the shields. 
     U.S. Pat. No. 5,828,530 to Gill et al. describe a spin valve sensor device wherein the spin valve sensor is asymmetrically located between first and second shield layers so that image currents from the first and second shield layers partially or completely counterbalances a stiffening field from antiferromagnetic, pinned, and spacer layers. 
     U.S. Pat. No. 5,883,763 to Yuan et al. describes a read/write head having a giant magnetoresistive sensor biased by permanent magnets located between the giant magnetoresistive element and the pole shields. 
     SUMMARY OF THE INVENTION 
     In most magnetic recording and sensing devices the sensing device and writing device are packaged in the same recording/sensing head. This close proximity of the sensing and writing device, along with other reasons, requires the use of magnetic shields around the magnetic sensing device. A conventional shielding arrangement is shown schematically in FIGS. 1 and 2. FIG. 1 shows a magnetic sensing device  18  disposed between a first magnetic shielding element  14  and a second magnetic shielding element, wherein both the first and second magnetic shielding elements are ferromagnetic material. A magnetic writing device  20 , such as an inductive coil, is shown between the second magnetic shielding element  16 , which typically also functions as a first pole piece for the writing means and a second pole piece  17  for the writing means. The magnetic sensing device  18  and the ends of the pole pieces are located a first distance  12  from the magnetic recording media  10 , such as a magnetic disk. 
     FIG. 2 shows a view of the magnetic recording and sensing device looking out of and perpendicular to the magnetic recording media  10  of FIG.  1 . The view of FIG. 2 is a taken perpendicular to the view shown in FIG.  1 . FIG. 2 shows the magnetic sensing device  18  between the conventional first magnetic shielding element  14  and conventional second magnetic shielding element  16 . The conventional second magnetic shielding element  16  is shown between the magnetic sensing unit  18  and the second pole piece  17 . 
     One of the problems encountered in the conventional shielding arrangement is that the strong magnetic fields used for writing data into the magnetic media can rearrange the domain patterns of the first shielding element  14  and the second shielding element  16  used to shield the magnetic sensing device  18 . After the writing cycle has been completed the domains in the first and second shield elements will relax to their final domain state. Since these shields are magnetically coupled to the magnetic sensor device  18 , this relaxation of the domains to the final domain state will cause magnetic field fluctuations at the magnetic sensor device  18 . 
     The magnetic sensing device  18  comprises sensing elements such as a spin valve, anisotropic magnetoresistive, spin dependent tunneling magnetic sensing head or other giant magnetoresistive magnetic sensing head which are sensitive to the magnetic field fluctuations. These magnetic field fluctuations caused by the relaxing of the domains to their final state in the first and second shield elements will cause noise, such as pop-corn noise and covariance of amplitude noise, in the sense signal from the magnetic sensing device and complicate the process of reading the data stored in the magnetic media. 
     It is a principle objective of this invention to provide a magnetic shielding element which will not cause noise in the sensing signal of a magnetoresistive sensing device because of domains in the shielding material relaxing to their final state. 
     It is another principle objective of this invention to provide a magnetic recording and sensing device which will not have noise in the sensing signal of a magnetoresistive sensing device because of domains in the material used to shield the magnetic sensing device relaxing to their final state. 
     These objectives are achieved by forming new shielding elements. These shielding elements have a layer of antiferromagnetic exchange material formed on a layer of first ferromagnetic material. The first ferromagnetic material is stabilized by the antiferromagnetic exchange material to form a single domain state. A layer of non-magnetic metal is then formed on the layer of antiferromagnetic exchange material. A layer of second ferromagnetic material is then formed on the layer of non-magnetic metal to complete the shield element. The shield element is also the first pole piece of the magnetic writing means. 
     The magnetic fields used during the writing cycle will disturb both the domains in the layer of single domain first ferromagnetic material and the layer of second ferromagnetic material. However, the domains in the single domain first ferromagnetic material will relax to its single domain state with a relaxation time of pico seconds so that the single domain first ferromagnetic material will be completely relaxed to its single domain state before any data is read by the magnetic sensing device. The magnetic shielding elements are arranged so that the magnetic sensing device is between two magnetic shielding elements wherein the layer of single domain first ferromagnetic material of each shielding element is adjacent to the magnetic sensing device. The layer of single domain first ferromagnetic material of each shielding element shields the magnetic sensing device from the slower relaxation of the domains of the second ferromagnetic layer in each of the shielding elements. This arrangement shields the magnetic sensing device from magnetic field fluctuations and the problems of pop-corn noise and covariance of amplitude noise during readback of data from the disk are avoided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic view of a conventional magnetic shielding arrangement for a magnetic recording and sensing device. 
     FIG. 2 shows another schematic view of a conventional magnetic shielding arrangement for a magnetic recording and sensing device. 
     FIG. 3A shows a schematic view of the magnetic shielding arrangement of this invention for a magnetic recording and sensing device using two composite shielding elements. 
     FIG. 3B shows a schematic view of the magnetic shielding arrangement of this invention for a magnetic recording and sensing device using one composite shielding element and a shielding element of a single layer of ferromagnetic material. 
     FIG. 4 shows a cross section view of a layer of single domain first ferromagnetic material, a layer of antiferromagnetic exchange material, and a layer of non-magnetic metal. 
     FIG. 5 shows a cross section view of a magnetic shielding element of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Refer now to FIG. 3A for a description of a first embodiment of the magnetic shielding arrangement of this invention. FIG. 3A shows a view of the shielding arrangement looking out of the magnetic media  10  shown in FIG.  1 . FIG. 3A shows a magnetic sensing device  18  between a first magnetic shielding element  19  and a second magnetic shielding element  15 . The first magnetic shielding element  19  is between the magnetic sensing device  18  and the second pole piece  17  of the magnetic writing means. The first magnetic shielding element  19  also serves as the first pole piece of the magnetic writing means. The magnetic sensing device  18  comprises sensing elements such as a spin valve, anisotropic magnetoresistive, spin dependent tunneling magnetic sensing head or other giant magnetoresistive magnetic sensing head. 
     As shown in FIG. 3A, the magnetic sensing device  18  is between the first magnetic shielding element  19  and the second magnetic shielding element  15 . In this embodiment the first magnetic shielding element  19  and the second magnetic shielding element  15  have the same construction. As shown in FIG. 3A, both the first magnetic shielding element  19  and the second magnetic shielding element  15  have a layer of first ferromagnetic material  28  having a first thickness  38 . The layer of first ferromagnetic material  28  is formed on a layer of antiferromagnetic exchange material  26  having a second thickness  36 . The layer of first ferromagnetic material  28  is stabilized by the layer of antiferromagnetic exchange material  26  to form a single domain state. The antiferromagnetic exchange material  26  must be oriented so that the pinning field strength is parallel to the air bearing surface. The air bearing surface is shown as a dashed line  34  in FIG.  1  and in FIG. 3A is parallel to the plane of the paper. 
     The first thickness  38  and second thickness  36  must be optimized so that the pinning field strength is strong enough to prevent multi-domain states in the single domain first ferromagnetic material  28  but not strong enough to significantly lower the permeability of the single domain first ferromagnetic material  28 . In this example the first thickness  38  is between about 1000 and 5000 Angstroms and the second thickness  36  is between about 50 and 500 Angstroms. The first ferromagnetic material  28  can be regular permalloy like, Ni 80 Fe 20 , or a high B s  material, like Ni 45 Fe 55 . The first ferromagnetic material  28  can be one or a combination of two or more of Ni, NiFe, Co, CoFe, CoZrTa, CoZrNb, FeN, PeNAl, FeNTa, FeNNb, or FeNZr. The antiferromagnetic exchange material  26  can be one of either IrMn, RhMn, RuMn, RuRhMn, FeMn, FeMnRh, FeMnCr, CrPtMn, TbCo, NiMn, PtMn, PtPdMn, NiO, CoO, or CoNiO. 
     As shown in FIG. 3A a layer of non-magnetic metal  24  is then formed on the layer of antiferromagnetic exchange material  26 . The non-magnetic metal can be one of either V, Nb, Ta, Ti, Zr, Hf, Mo, W, or Cr. A layer of second ferromagnetic material  22  is then formed on the layer of antiferromagnetic exchange material  26 . The second ferromagnetic material  22  can be one or a combination of two or more of Ni, NiFe, Co, CoFe, CoZrTa, CoZrNb, FeN, FeNAl, FeNTa, FeNNb, or FeNZr. 
     As shown in FIG. 3A, the first magnetic shielding element  19 , the second magnetic shielding element  15 , and the magnetic sensing device  18  are arranged so that the magnetic sensing device  18  is between the first magnetic shielding element  19  and the second magnetic shielding element  15 , the layer of single domain first ferromagnetic material  28  of the first shielding element  19  is adjacent to the magnetic sensing device  18 , and the layer of single domain first ferromagnetic material  28  of the second shielding element  15  is adjacent to the magnetic sensing device  18 . 
     The magnetic fields used during the writing cycle will disturb both the domains in the layer of single domain first ferromagnetic material  28  and the layer of second ferromagnetic material  22 . However, the domains in the single domain first ferromagnetic  28  material will relax to its single domain state with a relaxation time of pico seconds so that after a write cycle the single domain first ferromagnetic material  28  will be completely relaxed to its single domain state before any data is read by the magnetic sensing device  18 . This relaxed layer of single domain first ferromagnetic material  28  will shield the magnetic sensing device  18  from field fluctuations due to domain relaxation in the layer of second ferromagnetic material  22  during read cycles which occur before the domains in the layer of second ferromagnetic material  22  have reverted to their relaxed state. 
     Refer now to FIG. 3B for a description of a second embodiment of the magnetic shielding arrangement of this invention. FIG. 3B shows a view of the shielding arrangement looking out of the magnetic media  10  shown in FIG.  1 . FIG. 3B shows a magnetic sensing device  18  between a first magnetic shielding element  19  and a third magnetic shielding element  23 . The first magnetic shielding element  19  is between the magnetic sensing device  18  and the second pole piece  17  of the magnetic writing means. The first magnetic shielding element  19  also serves as the first pole piece of the magnetic writing means. The magnetic sensing device  18  comprises sensing elements such as a spin valve, anisotropic magnetoresistive, spin dependent tunneling magnetic sensing head or other giant magnetoresistive magnetic sensing head. 
     As shown in FIG. 3B, the magnetic sensing device  18  is between the first magnetic shielding element  19  and the third magnetic shielding element  23 . In this embodiment the first magnetic shielding element  19  has the same construction as the first magnetic shielding element of the previous embodiment. As shown in FIG. 3B, the first magnetic shielding element  19  has a layer of first ferromagnetic material  28  having a first thickness  38 . The layer of first ferromagnetic material  28  is formed on a layer of antiferromagnetic exchange material  26  having a second thickness  36 . The layer of first ferromagnetic material  28  is stabilized by the layer of antiferromagnetic exchange material  26  to form a single domain state. The antiferromagnetic exchange material  26  must be oriented so that the pinning field strength is parallel to the air bearing surface. The air bearing surface is shown as a dashed line  34  in FIG.  1  and in FIG. 3B is parallel to the plane of the paper. 
     The first thickness  38  and second thickness  36  must be optimized so that the pinning field strength is strong enough to prevent multi-domain states in the single domain first ferromagnetic material  28  but not strong enough to significantly lower the permeability of the single domain first ferromagnetic material  28 . In this example the first thickness  38  is between about 1000 and 5000 Angstroms and the second thickness  36  is between about 50 and 500 Angstroms. The first ferromagnetic material  28  can be regular permalloy like, Ni 80 Fe 20 , or a high B s  material, like Ni 45 Fe 55 . The first ferromagnetic material  28  can be one or a combination of two or more of Ni, NiFe, Co, CoFe, CoZrTa, CoZrNb, FeN, FeNAl, FeNTa, FeNNb, or FeNZr. The antiferromagnetic exchange material  26  can be one of either IrMn, RhMn, RuMn, RuRhMn, FeMn, FeMnRh, FeMnCr, CrPtMn, TbCo, NiMn, PtMn, PtPdMn, NiO, CoO, or CoNiO. 
     As shown in FIG. 3B a layer of non-magnetic metal  24  is then formed on the layer of antiferromagnetic exchange material  26 . The non-magnetic metal can be one of either V, Nb, Ta, Ti, Zr, Hf, Mo, W, or Cr. A layer of second ferromagnetic material  22  is then formed on the layer of antiferromagnetic exchange material  26 . The second ferromagnetic material  22  can be one or a combination of two or more of Ni, NiFe, Co, CoFe, CoZrTa, CoZrNb, FeN, FeNAl, FeNTa, FeNNb, or FeNZr. 
     Referring again to FIG. 3B, in this embodiment the third shielding element  23  is formed of a layer of third ferromagnetic material  21  and not the stacked structure used for the first shielding element  19 . The third ferromagnetic material  21  can be one or a combination of two or more of Ni, NiFe, Co, CoFe, CoZrTa, CoZrNb, FeN, FeNAl, FeNTa, FeNNb, or FeNZr. 
     As shown in FIG. 3B, the first magnetic shielding element  19 , the third magnetic shielding element  23 , and the magnetic sensing device  18  are arranged so that the magnetic sensing device  18  is between the first magnetic shielding element  19  and the third magnetic shielding element  23 . The layer of single domain first ferromagnetic material  28  of the first shielding element  19  is adjacent to the magnetic sensing device  18 . 
     The magnetic fields used during the writing cycle will disturb the domains in the layer of single domain first ferromagnetic material  28  and the layer of second ferromagnetic material  22  in the first shielding element  19 . However, the domains in the single domain first ferromagnetic  28  material in the first shielding element  19  will relax to its single domain state with a relaxation time of pico seconds so that after a write cycle the single domain first ferromagnetic material  28  in the first shielding element  19  will be completely relaxed to its single domain state before any data is read by the magnetic sensing device  18 . This relaxed layer of single domain first ferromagnetic material  28  in the first shielding element  19  will shield the magnetic sensing device  18  from field fluctuations due to domain relaxation in the layer of second ferromagnetic material  22  in the first shielding element  19  during read cycles which occur before the domains in the layer of second ferromagnetic material  22  in the first shielding element  19  have reverted to their relaxed state. 
     The domains of the layer of third ferromagnetic material  21  in the third shielding element  23  will be only slightly affected by the magnetic fields used during the writing cycle because the third shielding element  23  is not part of the magnetic circuit of the writing means. In addition, the disturbance of the domains of the third ferromagnetic material in the third shielding element  23  is small because of the relatively large distance between the third shielding element  23  and the gap  25  between the first shielding element  19 , which is also the first pole piece of the magnetic writing means, and the second pole piece  17 . 
     Refer now to FIGS. 4 and 5 for cross section views of a magnetic shielding element of this invention which describe the fabrication of the magnetic shielding elements. The layer of first ferromagnetic material  28 , the layer of antiferromagnetic exchange material  26 , and the layer of non-magnetic metal  24  are formed by sputtering, see FIG.  4 . The layer of first ferromagnetic material  28  is stabilized by the layer of antiferromagnetic exchange material  26  to form a single domain state. This composite of the layer of single domain first ferromagnetic material  28 , the layer of antiferromagnetic exchange material  26 , and the layer of non-magnetic metal  24  is then used as a new seed layer to replace the normal seed layer for plating the layer of second ferromagnetic material  22 , see FIG.  5 . 
     In this description of the materials used in the various embodiments of this invention standard symbols for elements are used so that Al is Aluminum, Co is Cobalt, Cr is Chromium, Fe is Iron, Hf is Halfnium, Ir is Iridium, Mn is Manganese, Mo is Molybdenum, N is Nitrogen, Nb is Niobium, Ni is Nickel, O is Oxygen, Pd is Palladium, Pt is Platinum, Rh is Rhodium, Ru is Ruthenium, Ta is Tantalum, Tb is Terbium, Ti is Titanium, V is Vanadium, W is Tungsten, and Zr is Zirconium. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.