Perpendicular Magnetic Recording Disk Permeability Gradient
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Solution Overview
Problem
Perpendicular magnetic recording disks face challenges in maintaining uniform magnetic write width (MWW) across different radii due to varying data recording frequencies, leading to non-uniform track widths and reduced areal densities.
Innovation Solution
A soft magnetic underlayer (SUL) with a permeability gradient from the inner radius to the outer radius is implemented, achieved by increasing the thickness of the SUL or the antiparallel coupling layer, which decreases the exchange field and enhances permeability, resulting in a uniform MWW throughout the disk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If data recording frequency is increased for outer tracks to achieve uniform linear density, then linear density is improved, but magnetic write width becomes smaller leading to non-uniform track width
Solution Approach 1:
The SUL structure is designed with spatially varying properties: the thickness of the SUL or antiparallel coupling layer increases from inner radius to outer radius of the disk, creating a permeability gradient. This local variation in permeability compensates for the frequency-dependent MWW changes, maintaining uniform track width across different radii despite different recording frequencies
Solution Approach 2:
The invention changes the permeability parameter of the SUL structure as a function of radius. By increasing permeability from inner to outer radius, the system compensates for the decrease in MWW at higher recording frequencies on outer tracks, thereby maintaining uniform MWW across the entire disk surface
2Quantity of substance
If track density is increased to achieve higher areal density, then areal density is improved, but maintaining uniform MWW becomes more difficult
Solution Approach 1:
The SUL structure implements local quality variation through a permeability gradient that increases from inner to outer radius. This spatially dependent permeability allows precise control of MWW at each radius, enabling high track density while maintaining uniform track width across the disk
Solution Approach 2:
By varying the permeability parameter of the SUL structure across the disk radius, the invention enables precise control of magnetic write width. This parameter change allows the system to achieve higher areal densities while maintaining uniform track width, as the permeability gradient compensates for frequency-dependent MWW variations
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 approach ensures a consistent MWW across the disk, enabling higher areal density recording by maintaining uniform track widths even at varying data recording frequencies.
Implementation Method 1
The soft magnetic underlayer (SUL) serves to concentrate a magnetic flux emitted from a main pole of a write head and to serve as a flux return path back to a return pole of the write head during recording on the magnetic recording layer
Implementation Method 2
A perpendicular magnetic recording disk having a permeability gradient... the permeability of the SUL structure increases from an inner radius of the disk to an outer radius of the disk
Implementation Method 3
the thicknesses of the first SUL and the second SUL increase from the inner radius to the outer radius. The increased thicknesses decrease the AP exchange field between the first SUL and the second SUL from the inner radius to the outer radius resulting in an increased permeability
Data Source
AI summary
Perpendicular magnetic recording disks and methods of fabricating perpendicular magnetic recording disks are described. The perpendicular magnetic recording disk includes a soft magnetic underlayer (SUL) structure, an interlayer, and a perpendicular magnetic recording layer. The SUL structure has an increased permeability from an inner radius of the disk to an outer radius of the disk. As a result, the magnetic write width (MWW) on the tracks of the disk is substantially uniform throughout the disk.