Soft Magnetic Underlayer Stabilization via Fe-Co Alloy Composition
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Solution Overview
Problem
The existing soft magnetic under layers for perpendicular magnetic recording media face instability in antiferromagnetic coupling force due to variations in spacer layer thickness, leading to reduced magnetic permeability for high-frequency signals and writability issues.
Innovation Solution
A soft magnetic under layer composition of (Fe100-XCoX)100-YMY with 15≦X≦30 and 10≦Y≦30, where M is Ta, Ti, Zr, Nb, Cr, or B, and a spacer layer of Ru with a thickness between 0.10 to 0.50 nm, achieving a low maximum antiferromagnetic coupling force and high saturation magnetic flux density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a structure yielding the maximum value of antiferromagnetic coupling force is used, then the antiferromagnetic coupling force is maximized, but the variation of coupling force increases corresponding to spacer layer thickness, destabilizing the coupling
Solution Approach 1:
The patent changes the composition parameters of the soft magnetic layer from conventional Co-Fe-Al alloy to Fe-Co alloy with specific atomic ratios (Fe: 70-90 at%, Co: 10-30 at%). This parameter change reduces the maximum antiferromagnetic coupling force to 1/3 to 1/10 of conventional materials, which paradoxically stabilizes the coupling force against variations in spacer layer thickness and improves high-frequency magnetic permeability
Solution Approach 2:
The patent intentionally uses a spacer layer thickness (0.1-0.5 nm) that is thinner than what would maximize antiferromagnetic coupling force, operating in a partial action regime. This prevents the system from reaching the unstable maximum coupling state while maintaining sufficient coupling for noise reduction
2Quantity of substance
If Co-Fe-Al alloy is used for soft magnetic layer, then saturation magnetic flux density is high, but antiferromagnetic coupling force maximum value is high, reducing magnetic permeability toward high-frequency signals
Solution Approach 1:
The patent changes the material composition from Co-Fe-Al alloy to Fe-Co alloy with Al content reduced to 0-5 at%. This parameter change achieves saturation magnetic flux density of 1.8 T or more while reducing the maximum antiferromagnetic coupling force, thereby maintaining high magnetic permeability for high-frequency signals and improving writability
3Object-generated harmful factors
If antiferromagnetic coupling force is increased to reduce noise, then magnetic wall is fixed, but magnetic permeability for high-frequency signals is reduced, affecting writability
Solution Approach 1:
The patent optimizes the composition parameters of the Fe-Co alloy (Fe: 70-90 at%, Co: 10-30 at%) to achieve a balanced antiferromagnetic coupling force that is sufficient to fix the magnetic wall and reduce noise, but not so strong as to reduce magnetic permeability for high-frequency signals below acceptable levels, thereby maintaining both noise reduction and writability
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 stabilizes antiferromagnetic coupling, enhances magnetic permeability for high-frequency signals, and improves writability while maintaining high saturation magnetic flux density, suitable for perpendicular magnetic recording media.
Implementation Method 1
The soft magnetic layers are antiferromagnetically coupled through the spacer layer inserted therebetween
Implementation Method 2
must have a high magnetic permeability to enhance writability to a magnetic recording medium
Implementation Method 3
must have a high saturation magnetic flux density to efficiently draw in a recording magnetic field
Data Source
AI summary
A soft magnetic under layer has a low antiferromagnetic coupling force and a high saturation magnetic flux density. The soft magnetic under layer includes two soft magnetic layers and a spacer layer. The soft magnetic layers are expressed by a composition formula as (Fe100-XCoX)100-Y-MY by atomic ratio, wherein 15≦X≦30, 10≦Y≦30, and an element M is at least one element selected from a group of Ta, Ti, Zr, Nb, Cr, and B; are composed of residual incidental impurities; and each have a thickness of 10 to 50 nm. The spacer layer is composed of one element selected from a group of Ru, Cr, Cu, Re, and Rh and has a thickness of 0.10 to 0.50 nm. The soft magnetic layers are antiferromagnetically coupled through the spacer layer inserted therebetween. An antiferromagnetic coupling force between the soft magnetic layers is 100 to 4,000 A/m.