Perpendicular Magnetic Recording Medium with Exchange Coupling Control
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Solution Overview
Problem
Perpendicular magnetic recording media face challenges in achieving high recording density while maintaining writing performance and thermal stability, as miniaturization of ferromagnetic grains leads to reduced magnetization switching fields and increased thermal fluctuations, and exchange coupling control media struggle with narrow track pitch due to cross-track recording field components.
Innovation Solution
A magnetic recording layer configuration with specific anisotropy constants relationships (Ku4 > Ku3 > Ku2 and Ku1 > Ku3 > Ku2) and the inclusion of exchange coupling control layers to manage the switching field and prevent unintended writing into adjacent tracks, featuring a structure with multiple magnetic layers and exchange coupling control layers to optimize down-track writing and reduce cross-track interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ferromagnetic grains are miniaturized to increase recording density, then recording density is improved, but thermal stability deteriorates due to thermal fluctuations
Solution Approach 1:
The patent changes the magnetic anisotropy energy parameter Ku by using a granular structure with oxide grain boundary components (SiO2, Cr2O3, TiO2) instead of conventional non-oxide materials. This increases Ku to compensate for thermal fluctuations in miniaturized grains, maintaining thermal stability while achieving high recording density
Solution Approach 2:
The magnetic recording layer uses a composite granular structure consisting of ferromagnetic crystal grains (Co, Pt, Cr-based) surrounded by non-magnetic oxide grain boundary components. This composite structure provides both high Ku for thermal stability and sufficient exchange coupling for writing performance
2Reliability
If Ku is increased to improve thermal stability, then thermal stability is improved, but writing performance deteriorates due to insufficient magnetic field strength
Solution Approach 1:
The patent creates local quality variations by forming a granular structure where ferromagnetic grains with high Ku are surrounded by soft magnetic regions. This local soft magnetic environment reduces the effective switching field while maintaining high Ku for thermal stability, resolving the contradiction between writing performance and thermal stability
3Productivity
If ferromagnetic grains are miniaturized to increase recording density, then recording density is improved, but writing performance deteriorates due to reduced demagnetizing field
Solution Approach 1:
The patent changes the magnetic parameter Ku by introducing oxide grain boundary components, which increases magnetic anisotropy energy. This compensates for the reduced demagnetizing field in miniaturized grains, maintaining sufficient switching field for writing while achieving high recording density
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 enhances writing performance, signal quality, and thermal stability, allowing for high track density by controlling the magnetization switching and reducing cross-track interference, thereby improving recording performance and stability.
Implementation Method 1
a layer with a low Ku is disposed in a portion nearest to the magnetic head. As a result of diligent study by the inventor, it is found that an exchange coupling control medium with this kind of structure is disadvantageous in narrowing the track pitch
Implementation Method 2
a back layer of a soft magnetic material that fulfills a role of concentrating magnetic flux emitted by a magnetic head used in a recording onto the recording layer
Implementation Method 3
a structure called a granular structure, wherein ferromagnetic crystal grains are surrounded and magnetically divided by a non-magnetic grain boundary component
Data Source
AI summary
A perpendicular magnetic recording medium is disclosed that enables a high track density while maintaining good OW characteristics, SNR, and thermal stability. The medium includes a magnetic recording layer on a non-magnetic base, wherein the magnetic recording layer includes a first magnetic layer, a first exchange coupling control layer, a second magnetic layer, a third magnetic layer, and a fourth magnetic layer, in that order. It is preferable that when the perpendicular magnetic anisotropy constants of the first magnetic layer, second magnetic layer, third magnetic layer, and fourth magnetic layer are Ku1, Ku2, Ku3, and Ku4 respectively, relationships of Ku4>Ku3>Ku2 and Ku1>Ku3>Ku2 are satisfied.