Bias Layer and Shield Biasing Design

Abstract

A read head is longitudinally biased unidirectionally by laterally abutting soft magnetic layers or multilayers. The soft magnetic layers are themselves magnetically stabilized by layers of antiferromagnetic material that are exchange coupled to them. The same layers of antiferromagnetic materials can be used to stabilize a unidirectional anisotropy of an overhead shield by means of exchange coupling. By including the antiferromagnetic material layer within the patterned biasing structure itself, an additional layer of antiferromagnetic material that normally covers the entire sensor structure is eliminated. The elimination of an entire layer is also advantageous for reducing the inter-sensor spacing in a TDMR (two dimensional magnetic recording) configuration where two sensor are vertically stacked on top of each other.

What is claimed is: 
     
         1 . A read head having a longitudinally biased freelayer with unidirectional anisotropy in said longitudinal direction, comprising:
 a top shield;   a bottom shield   a patterned sensor placed between said top and bottom shields wherein said patterned sensor includes said freelayer having a unidirectional magnetic anisotropy aligned in a horizontal direction;   a layer of dielectric material contiguous with lateral patterned sides of said sensor;   a pair of soft magnetic films or a pair of multilayers of soft magnetic films symmetrically abutting said layer of dielectric material and biasing said freelayer along said direction of unidirectional magnetic anisotropy;   a pair of antiferromagnetic layers exchange coupled to said soft magnetic biasing layers or said multilayer of soft magnetic biasing layers and, thereby, stabilizing said biasing of said freelayer; wherein   said top shield is also biased in the same direction as said freelayer and wherein said top shield is exchange coupled to said pair of antiferromagnetic layers and is also provided with a unidirectional magnetic anisotropy and stabilized thereby.   
     
     
         2 . The read head of  claim 1  wherein each of said pair of antiferromagnetic layers is formed on top of said soft magnetic biasing layers or said multilayer formation of soft magnetic biasing layers. 
     
     
         3 . The read head of  claim 1  wherein each of said pair of antiferromagnetic layers is sandwiched between a pair of soft magnetic biasing layers and thereby directly couples to each of said soft magnetic biasing layers that reside above and below said sandwiched antiferromagnetic layer. 
     
     
         4 . The read head of  claim 2  wherein each of said pair of antiferromagnetic layers formed on the top of said soft magnetic biasing layers or on the top of said multilayered formation is exchange coupled to said top shield layer and thereby provides a unidirectional magnetic anisotropy to said top shield layer as well as said biasing layers. 
     
     
         5 . The read head of  claim 3  wherein each of said pair of antiferromagnetic layers sandwiched between and directly coupled to each of a pair of soft magnetic biasing layers is also exchange coupled to said top shield layer thereby providing a unidirectional magnetic anisotropy to said top shield layer as well as said pair of soft magnetic biasing layers. 
     
     
         6 . The read head of  claim 1  wherein said soft magnetic biasing layer is a multilayer of soft magnetic layers and wherein adjacent pairs of soft magnetic layers may be antiferromagnetically coupled, while possessing a net magnetic moment by virtue of having different thicknesses, by means of an intermediate antiferromagnetically coupling layer. 
     
     
         7 . The read head of  claim 6  wherein either or both individual layers of antiferromagnetically coupled adjacent pairs of soft magnetic layers may be exchange coupled to an antiferromagnetic layer. 
     
     
         8 . The read head of  claim 1  wherein said soft magnetic biasing layer or multilayers may be formed of the soft magnetic alloys NiFe, CoFe, FeCo, Fe or their combinations. 
     
     
         9 . The read head of  claim 6  wherein said layer of antiferromagnetically coupling material is a layer of Ru and wherein said antiferromagnetic coupling is a negative exchange coupling. 
     
     
         10 . The read head of  claim 1  wherein said exchange coupling produces said unidirectional anisotropy as a result of an annealing process carried out at a temperature of between 200-250 deg. C., for a period of approximately 2 hours in a saturating magnetic field.