Magnetic Head Shield Layer Thermal Expansion Control
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Solution Overview
Problem
Magnetic heads for perpendicular magnetic recording face challenges in achieving high recording density and external field durability, particularly due to thermal instability and distortion effects on shield layers, which affect read and write performance.
Innovation Solution
A magnetic head with a CPP structure is designed, featuring a multi-layered shield structure using low thermal expansion non-magnetic materials for both upper and lower magnetic shield layers, along with a gap layer, to enhance thermal stability and external field durability, thereby reducing erroneous writing and erasure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a CPP structure is used for the read head to achieve narrower shield-to-shield distance and higher recording density, then the magnetic track width is reduced and recording density is enhanced, but the sensor film becomes susceptible to distortion effects from shield layers, degrading read performance
Solution Approach 1:
The patent changes the material parameter of the shield layer from conventional high thermal expansion materials to low thermal expansion materials (coefficient of thermal expansion ≤ 11.5×10^-6 /°K). This parameter change reduces thermal distortion of the shield layer, thereby protecting the sensor film from distortion effects and maintaining read performance stability while enabling narrower shield-to-shield distance for higher recording density
Solution Approach 2:
The patent employs composite material structure for the shield layer, combining low thermal expansion non-magnetic materials with magnetic materials. This composite approach provides both thermal stability to protect the sensor film and magnetic shielding functionality, resolving the contradiction between achieving narrow track width and maintaining read performance
2Ease of manufacture
If conventional shield layers are used in the CPP structure, then manufacturing is simpler, but thermal distortion occurs during annealing processes, affecting sensor film performance
Solution Approach 1:
The patent specifies a particular parameter range for the shield layer material (coefficient of thermal expansion ≤ 11.5×10^-6 /°K) to achieve dimensional stability during annealing. This parameter specification allows conventional manufacturing processes to be used while preventing thermal distortion, thus maintaining both ease of manufacture and compositional stability
3Productivity
If the shield-to-shield distance is reduced to achieve narrower magnetic track width, then recording density increases, but the shielding effect is weakened, allowing external fields to converge and cause erroneous writing
Solution Approach 1:
The patent changes the material parameter of the shield layer to low thermal expansion material, which stabilizes the shield layer dimensions and enhances its shielding effectiveness. This allows the shield-to-shield distance to be reduced for narrower track width while maintaining adequate shielding against external fields, thus preventing erroneous writing
Solution Approach 2:
The patent uses composite material structure combining low thermal expansion non-magnetic materials with magnetic materials in the shield layer. This composite approach provides both dimensional stability to maintain shielding geometry and magnetic properties to block external fields, enabling reduced shield-to-shield distance without compromising protection against external field convergence
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 achieves stable read and write performance with improved thermal stability and external field durability, maintaining a high magnetoresistive ratio even after annealing, thus ensuring reliable data storage.
Implementation Method 1
using low thermal expansion non-magnetic materials for both upper and lower magnetic shield layers... having a coefficient of thermal expansion smaller than that of a magnetoresistive film
Implementation Method 2
maintaining a high magnetoresistive ratio even after annealing
Data Source
AI summary
Embodiments in accordance with the present invention provide a magnetic head of the CPP structure for perpendicular magnetic recording, that is excellent in read performance, and stable in write/read performances by enhancing the external field durability, and further, suppresses deterioration in read sensor property, due to thermal factors. At least either shield layer of a lower magnetic shield layer, and an upper magnetic shield layer, closer to a perpendicular magnetic write head, is made up so as to have a multi-layered structure comprising low thermal expansion nonmagnetic layers, and magnetic layers. Material having a coefficient of thermal expansion smaller than that of a magnetoresistive film is selected as a material for the low thermal expansion nonmagnetic layers of the shield layer.