High moment laminated layer with nickel cobalt or nickel...

Details High moment laminated layer with nickel cobalt or nickel... High moment laminated layer with nickel cobalt or nickel...

1998-12-02

2001-08-21

Cao, Allen T. (Department: 2754)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

C360S125330

Reexamination Certificate

active

06278590

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high moment laminated layer with a nickel cobalt or nickel iron cobalt based alloy layer for the first pole piece of a write head and more particularly to a high moment laminated layer with a Ni
70
Co
30
(wt. %) layer or a nickel iron cobalt based alloy layer.
2. Description of the Related Art
Information in a computer is stored in a device that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS to cause the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on moving media, such as in circular tracks of the aforementioned rotating disk.
A spin valve sensor has been recently employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer, and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to an air bearing surface (ABS) of the head and the magnetic moment of the free layer is located parallel to the ABS but is free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
In a merged magnetoresistive (MR) head the second shield layer of the read head also functions as the first pole piece layer in the write head. Because of the proximity of the second shield/first pole piece layer (S
2
/P
1
) to the spin valve sensor it is important that this layer be magnetically stable. In order to achieve this purpose the S
2
/P
1
layer is formed by plating or sputter deposition in the presence of a field that is parallel to the ABS in the plane of the S
2
/P
1
layer. The field orients the easy axis (e.a.) of the S
2
/P
1
layer in the direction of the field, namely parallel to the ABS and in the plane of the S
2
/P
1
layer. This orientation also means that the magnetic domains in the S
2
/P
1
layer in the vicinity of the sensor are also aligned with their longitudinal axes parallel to the ABS in the plane of the S
2
/P
1
layer. It is important that these domains retain their orientation as formed and not move around when subjected to extraneous fields such as fields from the write head or fields from the rotating magnetic disk. When these domain walls move noise is generated which is referred to in the art as Barkhausen noise. This noise seriously degrades the read signal of the read head. Further, if the domain walls do not come back to their original position the S
2
/P
1
layer exerts a differently oriented field on the free layer of the spin valve sensor. This changes the magnetic bias on the free layer causing read signal asymmetry.
Nickel iron (NiFe) with a composition of approximately Ni
81
Fe
19
(wt. %) has been typically employed for the S
2
/P
1
layer as well as the first shield layer (S
1
). Nickel iron (NiFe) is a soft magnetic material that provides good shielding of the spin valve sensor from magnetic fields except within the read gap where signals are sensed by the sensor. Nickel iron (NiFe) also has near zero magnetostriction so that after lapping the head to form the ABS there is near zero stress induced anisotropy. Unfortunately, however, nickel iron (NiFe) has a low intrinsic magnetic anisotropy (H
K
). Intrinsic magnetic anisotropy is the amount of applied field required to rotate the magnetic moment of the layer 90 degrees from an easy axis orientation. The intrinsic magnetic anisotropy of nickel iron (NiFe) is 2-5 oersteds (Oe). After the first shield layer (S
1
) and the S
2
/P
1
layers are formed they are subjected to unfavorable magnetic fields that are required in subsequent processing steps. The insulation layers of the insulation stack are hard baked in the presence of a magnetic field that is directed perpendicular to the ABS for the purpose of maintaining the magnetic spins of the antiferromagnetic pinning layer in the spin valve sensor oriented in a direction perpendicular to the ABS. After completion of the head, the head is subjected to an additional anneal in the presence of an external magnetic field directed perpendicular to the ABS for the purpose of resetting the spins of the pinning layer perpendicular to the ABS. These annealing steps reduce the anisotropy field of nickel iron (NiFe) to very low values of 0-1 Oe.
The field typically employed for maintaining the spins of the pinning layer during hard bake of the insulation stack is about 1500 Oe and the field for resetting the spins of the pinning layer after completion of the head is about 13 KG. Because of the low intrinsic magnetic anisotropy of a nickel iron (NiFe) shield layer the aforementioned anneals in subsequent processing can cause the easy axis and the magnetic domains of the shield layer to switch their orientation such that they are no longer parallel to the ABS. The magnetic field present in these anneals reduces or destroys the intrinsic anisotropy field that was created in the nickel iron (NiFe) when it was originally formed and may create an anisotropy field perpendicular to the ABS. This is a very unfavorable position for magnetic domains of a shield layer. When the shields are subjected to perpendicular fields from the write head during the write function or perpendicular fields from the rotating magnetic disk the magnetic domains will move. This causes Barkhausen noise which degrades the read signal and causes a potential change in biasing of the spin valve sensor which results in read signal asymmetry.
Accordingly, there is a strong felt need for a material for the first shield layer (S
1
) and for the second shield/first pole piece layer (S
2
/P
1
) layer that will remain stable after being subjected to heat and magnetic fields employed in processing steps subsequent to making the shield layers.
SUMMARY OF THE INVENTION
We have replaced the nickel iron (NiFe), typically employed in the first shield layer (S
1
) and the second shield/first pole piece (S
2
/P
1
) layer, with a nickel cobalt alloy, which is preferably Ni
70
Co
30
(wt. %), or a nickel iron cobalt alloy, which is preferably in the composition range Ni
0.81(100−x)+y
Fe
0.19(100−x)−y
Co
x
(wt. %) layer where 0.5≦x≦25 and −5≦y≦5. Another preferred composition is Ni
73
Fe
18
Co
9
(wt. %). The nickel cobalt or nickel iron cobalt can be formed by either plating

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