Antiferromagnetically Coupled Bias Layer for MR Head Stability

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Solution Overview

Problem

Conventional thin-film magnetic heads face challenges in maintaining a stable bias magnetic field due to variations in external magnetic fields and stress, which affects the reliability of read head output, and increasing the thickness or anisotropic energy of bias magnetic field applying layers is difficult without compromising recording density.

Innovation Solution

A magnetoresistive device with a bias magnetic field applying layer comprising a nonmagnetic intermediate layer and antiferromagnetically exchange-coupled first and second magnetic layers, where the first magnetic layer has a greater thickness than the second, and is disposed adjacent to the side surface of the magnetosensitive layer to enhance coercivity and stability of the bias magnetic field.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the thickness or anisotropic energy of bias magnetic field applying layers is increased to enhance coercivity and stabilize the bias magnetic field, then the reliability of read head output is improved, but the recording density deteriorates

Engineering Contradiction:

Improvestability of bias magnetic fieldVSAvoidrecording density

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The bias magnetic field applying layer is segmented into multiple sub-layers with different magnetic properties. Specifically, it includes a first bias magnetic field applying layer with high coercivity and a second bias magnetic field applying layer with lower coercivity, allowing each layer to contribute differently to the overall bias field stability without requiring excessive total thickness

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The bias magnetic field applying layer uses composite material structure combining ferromagnetic layers and antiferromagnetic layers. The antiferromagnetic layer provides exchange coupling to fix the magnetization direction of the ferromagnetic layer, enhancing coercivity without proportionally increasing layer thickness

Inventive Principle:

Principle #40Composite materials

2Device complexity

If conventional single-layer bias magnetic field applying layers are used, then the device complexity is low, but the stability of bias magnetic field deteriorates under external magnetic field variations and stress

Engineering Contradiction:

Improvestructure of bias magnetic field applying layerVSAvoidstability of bias magnetic field

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The bias magnetic field applying layer is divided into multiple sub-layers with different magnetic properties. Specifically, it includes a first bias magnetic field applying layer with high coercivity and a second bias magnetic field applying layer with lower coercivity, allowing each layer to contribute differently to the overall bias field stability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the magnetic parameters (coercivity, thickness, magnetization direction) of different sub-layers to optimize performance. The first bias magnetic field applying layer has higher coercivity and specific thickness range, while the second layer has lower coercivity, creating a gradient structure that enhances overall stability

Inventive Principle:

Principle #35Parameter changes

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 solution provides a stable bias magnetic field to the magnetosensitive layer, enhancing coercivity and maintaining recording density, thereby improving the reliability of the thin-film magnetic head by aligning the magnetization direction effectively.

Implementation Method 1

a first magnetic layer and a second magnetic layer which are antiferromagnetically exchange-coupled to each other through the nonmagnetic intermediate layer

Methodology Applied

Scientific EffectAntiferromagnetic exchange coupling: Magnetism

Implementation Method 2

applies to the magnetosensitive layer a bias magnetic field for bringing the magnetosensitive layer into a single magnetic domain state in the absence of any external magnetic field applied thereto

Methodology Applied

Scientific EffectMagnetic domain alignment: Magnetism

Data Source

PatentUS7898775B2Magnetoresistive device having bias magnetic field applying layer that includes two magnetic layers antiferromagnetically coupled to each other through intermediate layer

Publication Date: 2011.03.01 TDK CORP

AI summary

An MR element includes a free layer whose direction of magnetization changes in response to an external magnetic field. Two bias magnetic field applying layers are disposed adjacent to two side surfaces of the MR element. Each bias magnetic field applying layer includes a nonmagnetic intermediate layer, and a first magnetic layer and a second magnetic layer disposed to sandwich the intermediate layer. The first and second magnetic layers are antiferromagnetically exchange-coupled to each other through RKKY interaction.