Bilayer Magnetic Seed Layer for Read Transducer Thermal Stability

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Solution Overview

Problem

Conventional magnetic read transducers face performance issues at higher recording densities due to reduced thermal stability of the antiferromagnetic layer and unwanted magnetic anisotropy induced by the Ni0.5Fe0.5 seed layer, leading to increased noise and instability in the presence of external fields.

Innovation Solution

A bilayer magnetic seed layer comprising a Ni1-xFex layer and a Ni1-yFey layer is used, where x is at least 0.3 and not more than 1, and y is not more than 0.19, to improve the thermal stability and reduce magnetostriction, thereby enhancing the stability and performance of the read sensor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional Ni0.5Fe0.5 seed layer is used, then the thermal stability of the AFM layer is improved, but unwanted magnetic anisotropy is induced and magnetostriction increases

Engineering Contradiction:

Improvethermal stability of AFM layerVSAvoidmagnetic anisotropy and magnetostriction

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The single-layer NiFe seed layer is segmented into a bilayer structure with a NiFeB layer (low magnetostriction) and a NiFe layer (high magnetostriction). The NiFeB layer is positioned adjacent to the AFM layer to provide thermal stability, while the NiFe layer is positioned away from the AFM layer to contribute magnetostriction that enhances perpendicular magnetic anisotropy without directly contacting the AFM layer, thus avoiding unwanted effects.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the seed layer structure are assigned different material properties: the NiFeB layer (with low magnetostriction coefficient) is placed where thermal stability is needed (adjacent to AFM layer), while the NiFe layer (with high magnetostriction coefficient) is placed where magnetic anisotropy enhancement is desired (away from AFM layer). This local differentiation of material properties resolves the contradiction between thermal stability and magnetic anisotropy control.

Inventive Principle:

Principle #3Local quality

2Productivity

If recording density is increased, then storage capacity is improved, but shield-to-shield spacing is reduced leading to decreased AFM layer volume and thermal stability

Engineering Contradiction:

Improverecording densityVSAvoidthermal stability of AFM layer

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The invention changes the material composition parameters of the seed layer by introducing a NiFeB layer with specific magnetic properties (low magnetostriction coefficient) adjacent to the AFM layer. This parameter change in the seed layer's magnetic properties compensates for the reduced AFM layer volume, maintaining thermal stability even at higher recording densities where shield-to-shield spacing is reduced.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If a magnetic seed layer with high magnetization is used, then thermal stability is improved, but the free layer response amplitude and asymmetry are adversely affected

Engineering Contradiction:

Improvethermal stabilityVSAvoidfree layer response amplitude and asymmetry

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The seed layer is segmented into two functional layers: NiFeB layer for thermal stability (low magnetostriction) and NiFe layer for magnetic anisotropy control (high magnetostriction). This segmentation allows independent optimization of thermal stability and magnetic response characteristics, resolving the contradiction between thermal stability and free layer response quality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The NiFeB layer acts as an intermediary between the AFM layer and the NiFe layer. It provides thermal stability to the AFM layer while its low magnetostriction property prevents excessive magnetostriction from propagating to the free layer, thereby maintaining proper free layer response amplitude and asymmetry.

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The bilayer magnetic seed layer increases the coercivity of the pinned layer, reduces unwanted anisotropies, and improves the thermal stability of the sensor, leading to enhanced performance and reduced noise at higher recording densities.

Implementation Method 1

The conventional Ni0.5Fe0.5 seed layer 14 typically has a very large positive magnetostriction. The magnetostriction may adversely affect sensor 20 performance.

Methodology Applied

Scientific EffectMagnetostriction: Magnetostriction

Implementation Method 2

The pinned layer 26 typically has its magnetization pinned by the conventional AFM layer 18, for example via exchange interaction.

Methodology Applied

Scientific EffectExchange interaction:

Implementation Method 3

The conventional tunneling barrier layer 32 may allow conduction through the sensor 20 via tunneling.

Methodology Applied

Scientific EffectTunneling:

Data Source

PatentUS8638529B1Method and system for providing a magnetic read transducer having a bilayer magnetic seed layer

Publication Date: 2014.01.28 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A method and system for providing a magnetic read transducer is described. The magnetic read transducer includes a bilayer magnetic seed layer, an antiferromagnetic (AFM) layer, and a read sensor. The bilayer magnetic seed layer includes a Ni1-xFex layer and a Ni1-yFey layer on the Ni1-xFex layer, where x is at least 0.3 and not more than 1 and where y is not more than 0.19. The AFM layer resides on the bilayer magnetic seed layer. The read sensor is on the AFM layer.