Dual Free Layer Magnetic Read Sensor Asymmetry Compensation
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Solution Overview
Problem
Magnetic read heads with dual free layers face challenges in achieving balanced cross-track signal profiles due to asymmetrical bumps, which hinder areal density capability and increase sector error rates, especially in shingled magnetic recording systems.
Innovation Solution
A magnetic read head design incorporating a dual free layer configuration with specific layer arrangements, including antiferromagnetic layers, soft bias side shields, and nonmagnetic spacer layers, to reduce side bump imbalance and enhance reading performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dual free layer configuration is used to achieve better linear resolution and reduced head instability, then reading performance is improved, but asymmetrical bumps appear in the signal cross-track profile leading to side reading imbalance
Solution Approach 1:
The patent applies asymmetry by introducing a synthetic antiferromagnetic (SAF) structure with specific asymmetric layer configurations. The SAF structure includes a first antiferromagnetic layer coupled to a first ferromagnetic layer, and a second antiferromagnetic layer coupled to a second ferromagnetic layer, creating an asymmetric magnetic field distribution that compensates for the inherent asymmetry in dual free layer signals. This asymmetric design balances the cross-track signal profile by generating compensating fields that reduce the imbalanced bumps on either side of the track center.
2Stability of the object's composition
If dual free layers with finite down-track separation are used, then head instability is reduced, but asymmetrical bumps increase in the signal cross-track profile
Solution Approach 1:
The patent uses a nonmagnetic spacer layer as an intermediary between the dual free layers. This spacer layer maintains the finite down-track separation required for head stability while providing a controlled magnetic environment. Additionally, the synthetic antiferromagnetic structure acts as a mediator that generates compensating magnetic fields to counteract the asymmetrical bumps, thereby preserving both head stability and signal profile symmetry.
3Productivity
If shingled magnetic recording is used to increase cross-track track density, then areal density capability is improved, but write quality differential based on shingle direction increases due to asymmetrical bumps
Solution Approach 1:
The patent changes the magnetic field parameters by introducing the synthetic antiferromagnetic structure with specific layer thicknesses and magnetization directions. By adjusting the thickness of the nonmagnetic spacer layer and the configuration of the SAF structure, the magnetic field distribution is optimized to minimize write quality differential. This parameter optimization ensures uniform write quality in both shingle directions, enabling high cross-track track density without sacrificing manufacturing precision.
Data Source
AI summary
Aspects of the present disclosure generally relate to magnetic recording heads of magnetic recording devices, such as magnetic read sensors of magnetic read heads of hard disk drives (HDD). In one implementation, a reader includes a magnetic seed layer and a shield layer. Two free layers are disposed between the magnetic seed layer and the shield layer. The magnetic seed layer and the shield layer are magnetized in opposite directions. In one or more embodiments, each of the magnetic seed layer and the shield layer is magnetized using a simple pinning arrangement having an antiferromagnetic (AFM) layer. In one or more embodiments, one of the magnetic seed layer or the shield layer is magnetized using a simple pinning arrangement having an AFM) layer, and the other of the magnetic seed layer or the shield layer is magnetized using a synthetic antiferromagnetic (SAF) pinning arrangement having an AFM layer.