Perpendicular Magnetic Recording Medium Lateral Coupling Layer
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Solution Overview
Problem
Perpendicular magnetic recording media face challenges with thermal decay and high intrinsic media noise due to the susceptibility of magnetic grains, especially in exchange-spring structures, which affect thermal stability and writability.
Innovation Solution
A perpendicular magnetic recording medium with an exchange-spring structure incorporating a ferromagnetic lateral coupling layer (LCL) that mediates intergranular exchange coupling between two ferromagnetically exchange-coupled magnetic layers, allowing for tunable intergranular exchange and improved thermal stability and writability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an exchange-spring structure with granular ferromagnetic cobalt alloy is used in perpendicular magnetic recording, then thermal stability is improved through perpendicular magnetic anisotropy, but intrinsic media noise increases and thermal decay susceptibility increases due to weak intergranular exchange coupling
Solution Approach 1:
The patent applies local quality by creating distinct regions with different intergranular exchange coupling strengths. The lower magnetic layer (MAG1) has strong intergranular exchange coupling to reduce media noise and thermal decay, while the upper magnetic layer (MAG2) has weaker coupling to maintain perpendicular magnetic anisotropy and thermal stability. This spatial differentiation of coupling strength allows simultaneous optimization of both thermal stability and noise reduction.
Solution Approach 2:
The patent uses composite materials by combining granular ferromagnetic cobalt alloy layers with different compositions and coupling characteristics. The lower layer uses a cobalt alloy composition optimized for strong intergranular coupling, while the upper layer uses a composition that maintains perpendicular anisotropy. This composite structure enables the system to achieve both high thermal stability and low intrinsic media noise.
2Quantity of substance
If perpendicular magnetic recording with exchange-spring structure is used, then recording density is increased, but writability deteriorates due to high coercivity and long magnetization reversal time
Solution Approach 1:
The patent segments the recording layer into two distinct magnetic layers with different coercivity characteristics. The lower layer (MAG1) has higher coercivity for thermal stability, while the upper layer (MAG2) has lower coercivity to facilitate magnetization reversal during writing. This segmentation allows the medium to achieve high recording density while maintaining acceptable writability through the synergistic interaction between layers.
Solution Approach 2:
The patent applies parameter changes by varying the composition, thickness, and magnetic properties of the two layers. By adjusting parameters such as cobalt content, alloying elements, layer thicknesses, and interlayer coupling strength, the patent optimizes the balance between coercivity for thermal stability and reversibility for writability, enabling high-density recording with improved writeability.
3Object-generated harmful factors
If granular ferromagnetic cobalt alloy with segregants is used to reduce intergranular exchange coupling, then intrinsic media noise is reduced, but thermal decay susceptibility increases
Solution Approach 1:
The patent resolves this contradiction by transitioning from a single-layer structure to a two-layer vertical structure. Instead of further reducing intergranular coupling in a single layer (which would increase thermal decay), the patent adds a vertical dimension with two layers having different coupling strengths. The lower layer maintains strong coupling for thermal decay resistance, while the upper layer has weaker coupling for noise reduction, achieving both goals simultaneously.
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 medium achieves high signal-to-noise ratio (SNR) and thermal stability while enhancing writability by optimizing intergranular exchange coupling, reducing thermal decay, and minimizing magnetization reversal time.
Implementation Method 1
A perpendicular magnetic recording medium with an exchange-spring structure incorporating a ferromagnetic lateral coupling layer (LCL) that mediates intergranular exchange coupling between two ferromagnetically exchange-coupled magnetic layers
Implementation Method 2
two ferromagnetically exchange-coupled magnetic layers (MAG1 and MAG2), each with perpendicular magnetic anisotropy
Implementation Method 3
MAG1 and MAG2 may have a coupling layer (CL) located between them that permits tuning to the appropriate ferromagnetic inter-layer coupling strength between MAG1 and MAG2. The LCL is in direct contact with MAG1 and is located either above or below MAG1
Data Source
AI summary
A perpendicular magnetic recording system and medium has a multilayered recording layer that includes an exchange-spring structure and a ferromagnetic lateral coupling layer (LCL). The exchange-spring structure is made up of two ferromagnetically exchange-coupled magnetic layers (MAG1 and MAG2), each with perpendicular magnetic anisotropy. MAG1 and MAG2 may have a coupling layer (CL) located between them that permits ferromagnetic exchange coupling of MAG1 with MAG2. The LCL is located either above or below MAG1 and in direct contact with MAG1 and mediates an effective intergranular exchange coupling in MAG1. The ferromagnetic alloy in the LCL has significantly greater intergranular exchange coupling than the ferromagnetic alloy in MAG1, which typically will include segregants such as oxides. The LCL is preferably free of oxides or other non-metallic segregants, which would tend to reduce intergranular exchange coupling in the LCL. Because the LCL grain boundaries overlay the boundaries of the generally segregated and decoupled grains of MAG1, and the LCL and MAG1 grains are strongly coupled perpendicularly, the LCL introduces an effective intergranular exchange coupling in the MAG1.