Thin Film Magnetic Head Side Layers Compression Stress
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Solution Overview
Problem
The magnetization direction of the magnetization pinned layer in thin film magnetic heads becomes unstable under high temperature environments due to changes in stress state of the bias magnetic field application layers, particularly when soft magnetic layers are used, leading to fluctuations in magnetic field detection during high recording density operations.
Innovation Solution
A thin film magnetic head configuration with a spin-valve film including a magnetization pinned layer and side layers with soft magnetic bias magnetic field application layers, where the side layers apply compression stress to the magnetization pinned layer, maintaining its orientation perpendicular to the air bearing surface using a gap layer and a seed layer, such as MgO, to stabilize the magnetic field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If soft magnetic layers are used in bias magnetic field application layers to apply bias magnetic fields and shield external magnetic fields, then the magnetic field detection capability is improved, but the stress state changes under high temperature environments causing magnetization direction instability
Solution Approach 1:
The patent changes the stress parameter of the bias magnetic field application layer by introducing a compression stress generation structure. This structure includes a hard magnetic layer with high coercivity that maintains compression stress on the soft magnetic layer even under high temperature conditions, preventing the stress state change that would otherwise occur during annealing or operation.
Solution Approach 2:
The patent uses a composite structure combining soft magnetic layers with hard magnetic layers. The soft magnetic layer provides bias magnetic field application and external magnetic field shielding, while the hard magnetic layer provides stable compression stress. This composite approach allows the system to maintain both magnetic field detection capability and magnetization direction stability under high temperature conditions.
2Productivity
If the dimension of the SV film in the track width direction is reduced to increase recording density, then the recording density is improved, but the magnetization direction fluctuation becomes larger under high temperature environments
Solution Approach 1:
The patent applies local quality by concentrating the compression stress effect at the location of the magnetization pinned layer. The bias magnetic field application layers are positioned specifically adjacent to the SV film, and the compression stress is localized to the region where it can most effectively stabilize the magnetization pinned layer's magnetization direction, thereby maintaining stability even as the overall film dimension is reduced for higher recording density.
3Reliability
If compression stress is applied to the magnetization pinned layer to stabilize magnetization direction, then the magnetization direction stability is improved, but the stress state must be maintained under high temperature conditions which is difficult with soft magnetic layers alone
Solution Approach 1:
The hard magnetic layer acts as an intermediary element between the compression stress generation mechanism and the magnetization pinned layer. It receives the compression stress from the bias magnetic field application layer structure and transmits it stably to the magnetization pinned layer, maintaining the stress state under high temperature conditions where soft magnetic layers alone would fail.
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 configuration effectively stabilizes the magnetization direction of the magnetization pinned layer, maintaining a positive saturation magnetostriction coefficient and reducing the impact of external magnetic fields from adjacent tracks, thereby enhancing the SN ratio and output stability under high temperature conditions.
Implementation Method 1
the magnetization pinned layer has a positive saturation magnetostriction constant and is subjected to compression stress in the track width direction from side layers, causing the magnetization pinned layer to stretch in the height direction and induce a magnetic field in the height direction
Implementation Method 2
a bias magnetic field application layer that includes a soft magnetic layer and applies a bias magnetic field in the track width direction to the magnetization free layer
Implementation Method 3
a gap layer that is positioned between the spin valve film and the bias magnetic field application layer
Data Source
AI summary
A thin film magnetic head includes a spin valve film that includes a magnetization free layer, a magnetization pinned layer and a non-magnetic spacer layer that is disposed between the magnetization free and pinned layers, and a pair of side layers that are disposed at both sides of the spin valve film in a track width direction and at least in the vicinity of the magnetization free layer and the magnetization pinned layer. Each of the side layers has a bias magnetic field application layer that includes a soft magnetic layer and applies a bias magnetic field in the track width direction to the magnetization free layer, and a gap layer that is positioned between the spin valve film and the bias magnetic field application layer, and the side layers have compression stresses at least in the vicinity of the magnetization pinned layer.