CPP Magnetic Head Side Shields with Antiferromagnetic Exchange Coupling
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Solution Overview
Problem
Conventional thin film magnetic heads face challenges in achieving high recording density and linearity between external magnetic fields and signal outputs due to the thickness of antiferromagnetic layers and shape anisotropy effects in side shield layers, which lead to magnetization issues and dispersion in signal output.
Innovation Solution
The configuration includes a magnetoresistive stack with first and second MR magnetic layers, nonmagnetic intermediate layers, and side shield layers with antiferromagnetically exchange-coupled magnetic layers through a ruthenium layer, minimizing spontaneous magnetization and allowing only orthogonal bias magnetic fields to affect the MR layers, thereby enhancing track density and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional side shield layer made of NiFe is used, then the side shield layer can be easily manufactured, but it easily absorbs the bias magnetic field and becomes magnetized, deteriorating linearity between external magnetic field and signal output
Solution Approach 1:
The side shield layer is constructed as a composite structure with a CoFeB magnetic layer (thickness: 0.5-2.0 nm) and a Ru nonmagnetic layer (thickness: 0.3-1.0 nm). This composite structure provides both manufacturability and superior magnetic field control, resolving the contradiction between ease of manufacture and measurement precision.
Solution Approach 2:
The invention changes the material parameters by using CoFeB instead of conventional NiFe, and precisely controlling the thickness parameters of each layer (CoFeB: 0.5-2.0 nm, Ru: 0.3-1.0 nm). These parameter changes reduce spontaneous magnetization and improve linearity between external magnetic field and signal output.
2Speed
If the side shield layer is formed in a long and narrow shape to match the free layer height, then the response to external magnetic field is improved, but shape anisotropy effect causes magnetization in the lengthwise direction, increasing magnetic field interference
Solution Approach 1:
By changing the material composition to CoFeB and Ru, and optimizing the thickness parameters (CoFeB: 0.5-2.0 nm, Ru: 0.3-1.0 nm), the invention reduces spontaneous magnetization. This allows the side shield layer to maintain its long and narrow shape for fast response while minimizing shape anisotropy-induced magnetization and harmful magnetic field interference.
3Manufacturing precision
If the read gap is narrowed to increase track density, then the arrangement density is improved, but the antiferromagnetic layer thickness restricts further narrowing
Solution Approach 1:
The invention replaces the conventional thick antiferromagnetic layer structure with a composite side shield layer structure (CoFeB/Ru). This new composite structure enables further read gap narrowing to increase track density without the restrictions imposed by thick antiferromagnetic layers, while maintaining structural feasibility.
Solution Approach 2:
By changing the material system from conventional antiferromagnetic layers to CoFeB-based composite structure with optimized thickness parameters, the invention enables read gap narrowing beyond previous limits, thereby increasing track density without excessive film structure complexity.
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
This configuration effectively increases track density and improves the linearity between external magnetic fields and signal outputs by minimizing the influence of adjacent track magnetic fields and reducing magnetization effects, resulting in a more efficient and precise magnetic field detection.
Implementation Method 1
The two free layers are exchange-coupled based on RKKY (Rudermann, Kittel, Kasuya, Yoshida) interaction through the nonmagnetic intermediate layer
Implementation Method 2
The side shield layer having such a long and narrow shape tends to be magnetized in a lengthwise direction of the long and narrow shape by a shape anisotropy effect
Implementation Method 3
the magnetization directions of the two free layers change, the relative angle between the magnetization directions of the two free layers changes, and an electrical resistance of a sense current changes
Data Source
AI summary
A thin film magnetic head includes a magnetoresistive (MR) stack disposed between first and second shield layers in a direction orthogonal to the film surface; a first exchange-coupling layer that is positioned between the MR stack and the first shield layer; a second exchange-coupling layer that is positioned between the MR stack and the second shield layer; a bias magnetic field application layer that is disposed at an opposite surface of the MR stack from an air bearing surface (ABS); and pair of side shield layers that are positioned at both sides of the MR stack with respect to a track width direction. Each of the side shield layers includes a pair of magnetic layers that are antiferromagnetically exchange-coupled through a side shield ruthenium layer.