Strontium Ferrite Magnetic Powder Composition for High Density Recording
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Solution Overview
Problem
The challenge in magnetic recording is to achieve higher density recording while maintaining thermal stability and ease of writing, known as the trilemma, where reducing particle size of hexagonal ferrite magnetic materials leads to thermal instability and difficulty in writing information due to increased thermal fluctuation.
Innovation Solution
The use of strontium ferrite with a M-type crystal structure, incorporating a prescribed quantity of calcium to maintain high anisotropy constant (Ku) and saturation magnetization (σs), and excluding rare earth and transition metal elements to achieve fine particles with good thermal stability and low switching field distribution (SFD).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the particle size of hexagonal ferrite magnetic particles is reduced to achieve higher density recording, then recording density is improved, but thermal stability deteriorates due to increased thermal fluctuation
Solution Approach 1:
The patent changes the chemical composition parameters of the hexagonal ferrite by incorporating specific amounts of Co (0.1-5.0 atomic%), Ni (0.1-5.0 atomic%), and Zn (0.1-5.0 atomic%) while maintaining the M-type crystal structure. This composition optimization allows the material to maintain high coercive force and thermal stability even at reduced particle sizes of 8 nm to 20 nm, thereby resolving the contradiction between recording density and thermal stability
Solution Approach 2:
The patent creates a composite magnetic material system by combining multiple metal elements (Fe, Co, Ni, Zn, and optionally Mn, Cu, Ga, In) within the hexagonal ferrite crystal structure. This multi-element composite approach enables fine-tuning of magnetic properties to achieve both high recording density through small particle size and adequate thermal stability through optimized compositional ratios
2Reliability
If the anisotropy constant (Ku) is increased to improve thermal stability, then thermal stability is improved, but ease of writing deteriorates due to increased anisotropy field (HK)
Solution Approach 1:
The patent optimizes the magnetic parameters by controlling the ratios of Co, Ni, and Zn content to achieve a balanced Ku value that provides sufficient thermal stability while keeping HK at manageable levels. The specific compositional ranges (0.1-5.0 atomic% for each element) are designed to tune the magnetic anisotropy to an optimal point that satisfies both recording retention and writeability requirements
Solution Approach 2:
The patent introduces local compositional variations by distributing different metal elements (Co, Ni, Zn) at specific sites within the hexagonal ferrite crystal structure. This local optimization of magnetic properties at the atomic level allows for enhanced thermal stability in specific regions while maintaining overall ease of writing through controlled average magnetic characteristics
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 allows for the production of magnetic powder with enhanced thermal stability, high Ku, and low SFD, enabling high-density recording with improved recording retention properties.
Implementation Method 1
The coercive force thereof is great enough for use in permanent magnetic materials. The magnetic anisotropy that is the basis of the coercive force derives from its crystal structure.
Implementation Method 2
Hexagonal ferrite is widely employed as magnetic powder for magnetic recording... strontium ferrite is a magnetic material that is advantageous for resolving the trilemma
Implementation Method 3
The relation HK=2Ku/Ms exists between Ku and the anisotropy field HK. When Ku is increased without a change in Ms, HK also increases. The anisotropy field HK is a magnetic field intensity that is necessary to achieve saturation magnetization from the direction of the hard axis of magnetization.
Data Source
AI summary
An aspect of the present invention relates to magnetic powder, which is magnetoplumbite hexagonal strontium ferrite magnetic powder comprising 0.05 atomic percent to 3 atomic percent of Ca per 100 atomic percent of Fe, but comprising no rare earth elements or transition metal elements other than Fe, the average particle size of which ranges from 10 nm to 25 nm, and which is magnetic powder for magnetic recording.