Hexagonal Ferrite Magnetic Particle Core-Shell Structure
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Solution Overview
Problem
Conventional ferromagnetic metal powders face limitations in achieving high-density magnetic recording due to thermal fluctuation-induced superparamagnetism, while hexagonal ferrite magnetic materials exhibit high thermal stability but require a large external magnetic field for recording, compromising recording properties.
Innovation Solution
Heat-treating hexagonal ferrite magnetic materials in a reducing atmosphere containing hydrocarbon gas to create a core/shell structure with carbon components, which reduces the switching magnetic field and maintains thermal stability, thereby improving recording properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If ferromagnetic metal powders are used for high-density recording, then particle size can be reduced, but thermal fluctuation causes superparamagnetism and precludes use in magnetic recording media
Solution Approach 1:
The patent uses hexagonal ferrite magnetic material which combines the benefits of both ferromagnetic metals and oxide materials. The hexagonal ferrite structure provides high crystal magnetic anisotropy for thermal stability while maintaining ferromagnetic properties for recording, effectively creating a composite magnetic material that resolves the contradiction between small particle size and thermal stability.
Solution Approach 2:
The patent changes the material composition parameters by using substituted ferromagnetic ferrite with specific metal elements (Co, Ni, Zn, Mn, Al, Si, etc.) to adjust the magnetic properties. By controlling substitution ratios and particle size within specific ranges, the patent achieves optimal balance between thermal stability and recording performance.
2Reliability
If hexagonal ferrite magnetic material is used to maintain thermal stability, then high crystal magnetic anisotropy is achieved, but switching magnetic field increases resulting in high coercive force that requires large external magnetic field for recording
Solution Approach 1:
The patent reduces coercive force by controlling particle size within 5-200 nm range and by substituting metal elements in the hexagonal ferrite structure. The substitution of Fe with elements like Co, Ni, Zn, Mn, Al, and Si modifies the magnetic anisotropy and exchange interactions, thereby reducing the switching magnetic field while maintaining thermal stability.
Solution Approach 2:
The patent creates a core/shell structure where the interior maintains the hexagonal ferrite crystalline structure for thermal stability while the surface undergoes reduction to form a different magnetic phase. This local differentiation allows the core to provide thermal stability while the shell reduces the overall coercive force, resolving the contradiction between thermal stability and recording properties.
3Force
If reduction processing is applied to improve recording properties, then coercive force is reduced, but crystalline structure deteriorating thermal stability is compromised
Solution Approach 1:
The patent divides the magnetic particle into core and shell regions through selective reduction. The core maintains the original hexagonal ferrite crystalline structure responsible for thermal stability, while the shell undergoes reduction to form a different magnetic phase with lower coercive force. This segmentation allows simultaneous achievement of thermal stability and improved recording properties.
Solution Approach 2:
The reduction processing is applied locally to the particle surface rather than uniformly throughout the entire particle. The surface region undergoes reduction to lower coercive force while the interior core preserves the high-temperature stable hexagonal ferrite structure. This localized treatment resolves the contradiction between reducing coercive force and maintaining thermal stability.
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 method achieves a magnetic particle with a coercive force suitable for recording and high thermal stability, suitable for use in particulate magnetic recording media without requiring high-temperature processing, enhancing both recording properties and thermal stability.
Implementation Method 1
hexagonal ferrite magnetic material has high crystal magnetic anisotropy due to its crystalline structure and thus exhibits good thermal stability
Implementation Method 2
heat-treating a hexagonal ferrite magnetic material in reducing atmosphere containing hydrocarbon gas
Data Source
AI summary
An aspect of the present invention relates to a magnetic particle obtained by heat-treating a hexagonal ferrite magnetic material in reducing atmosphere containing hydrocarbon gas.