Bias Layer and Shield Biasing Design
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.
This is a Divisional application of U.S. patent application Ser. No. 14/848,376 filed on Sep. 9, 2015, which is herein incorporated by reference in its entirety and assigned to a common assignee.
BACKGROUND1. Technical Field
This disclosure relates generally to thin-film magnetoresistive read sensors and particularly to the use of biasing layers to stabilize magnetic freelayers in configurations that implement “two dimensional magnetic recording”.
2. Description
Magnetic recording heads can bias the reader freelayer by means of the fringe field of the so-called bias layers. This approach is taught by Yanagisawa et al. (U.S. Pat. No. 8,462,467 B2). The bias layer itself is usually a soft magnetic material, and needs to be stabilized by means of magnetic coupling, usually exchange coupling, to another 2nd magnetic layer which is itself stabilized by some means. Usually this 2nd magnetic layer is the upper shield (just above the bias layer) and is itself stabilized by an antiferromagnetic layer such as IrMn, as is taught by Garfunkel et al. (U.S. Pat. No. 8,514,524 B2).
It is instructive to examine the approach of Yanagasawa a bit more closely by examination of an illustration of the structure taught by him in schematic
Referring next to
Schemes such as this may work well when there are no geometry constraints and there is room for the antiferromagnetic film, C. However, for so called Two Dimensional Magnetic Recording (TDMR) designs, which employ two sensor structures formed one over the other, Garfunkel et al. (U.S. Pat. No. 8,824,106 B1) have shown that it is critical to minimize the film thicknesses and, correspondingly, the distance between the lower and upper sensors. There is a need to reduce this sensor-to-sensor distance while also providing improvements to the biasing.
SUMMARYThe object of this disclosure is to provide a read sensor that includes at least one sensor element and that is longitudinally biased to have a unidirectional magnetic anisotropy and stabilized using an intrinsic antiferromagnetic layer that allows removal of an antiferromagnetic layer previously used for stabilization.
Referring to schematic
Layer 90, therefore, serves two functions; it stabilizes both the biasing layer, 61, and also the upper shield, 50. It can be used in place of the antiferromagnetic film C, (30, of
Referring again to schematic
Subsequent to an annealing process, such as a 2 hour anneal at between 200-250 deg. C in a saturating field, each of this pair of antiferromagnetic layers 90 will exchange couple to the soft magnetic biasing layers, 61, below it to promote and stabilize unidirectional magnetic anisotropy in those layers. It should be noted that the biasing layers 61 require a large net moment in order to bias the sensor. For this reason, forming the biasing layers as synthetic antiferromagnetic structures (i.e., coupling them with opposite moments across a layer of Ru as in
In addition to stabilizing the biasing layers, the pair of patterned antiferromagnetic films, 90, will be exchange coupled to the top shield, 50, thereby providing the shield with a stable unidirectional magnetic anisotropy as well. Thus, layer 90 serves two functions; it stabilizes both the pair of bias layers, 61, and also the top shield 50. It can be used in place of the antiferromagnetic film C, 30, in prior art
Referring finally to
As
As is understood by a person skilled in the art, the present description is illustrative of the present disclosure rather than limiting of the present disclosure. Revisions and modifications may be made to methods, materials, structures and dimensions employed in forming and providing a single or multiple sensor read head with longitudinally disposed patterned antiferromagnetic stabilized biasing layers, while still forming and providing such a structure and its method of formation in accord with the spirit and scope of the present disclosure as defined by the appended claims.
Claims
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.
Type: Application
Filed: Nov 30, 2016
Publication Date: Mar 23, 2017
Inventors: Glen Garfunkel (San Jose, CA), Yan Wu (Cupertino, CA), Junjie Quan (Fremont, CA), Yewhee Chye (Hayward, CA)
Application Number: 15/364,304