Sr-Substituted Barium Ferrite Powder for High-Squareness Recording
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Solution Overview
Problem
Hexagonal barium ferrite magnetic powders face challenges in achieving high perpendicular squareness ratio and recording density due to their magnetocrystalline anisotropy constant Ku being lower than strontium ferrite, leading to poor orientation and SNR in magnetic recording media, especially when formed into fine particles.
Innovation Solution
A hexagonal barium ferrite magnetic powder with a specific composition range of Sr/(Ba+Sr) molar ratio between 0.01 and 0.15 and a Dx volume of 2,200 nm^3 or less, obtained through a process involving preliminary heat treatment and crystallization of an amorphous body, enhances the magnetocrystalline anisotropy constant Ku and improves the perpendicular squareness ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If hexagonal barium ferrite is used to reduce particle size for high recording density, then recording density improves, but perpendicular squareness ratio decreases due to low magnetocrystalline anisotropy constant
Solution Approach 1:
The invention changes the chemical composition parameters by introducing Sr to substitute Ba in hexagonal barium ferrite, specifically controlling the Sr/(Ba+Sr) molar ratio within 0.01-0.15. This compositional parameter change increases the magnetocrystalline anisotropy constant Ku, enabling fine particles to maintain high perpendicular squareness ratio and avoid superparamagnetism, thus resolving the contradiction between recording density and perpendicular squareness ratio
Solution Approach 2:
The invention creates a composite magnetic powder system by combining Ba, Sr, Fe, and substituting elements (Co, Zn, Ti, Sn, Nb, or V) in specific ratios. This composite approach leverages the high Ku of Sr-containing ferrite while maintaining the desirable properties of barium ferrite, achieving both high recording density and perpendicular squareness ratio through material composition optimization
2Strength
If Sr content is increased to improve magnetocrystalline anisotropy constant, then Ku increases, but tabular ratio decreases leading to poor orientation
Solution Approach 1:
The invention precisely controls the Sr content parameter by limiting the Sr/(Ba+Sr) molar ratio to 0.01-0.15, optimizing the balance between increasing Ku and maintaining tabular ratio. This parameter optimization ensures that the magnetic particles retain their tabular shape for good orientation while achieving sufficient magnetocrystalline anisotropy for high perpendicular squareness ratio
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 results in a significant improvement in the perpendicular squareness ratio and SNR of magnetic recording media, enabling higher recording density and signal-to-noise ratio, suitable for high-density recording applications.
Implementation Method 1
a step of crystallizing an amorphous body containing Sr as a constituent element of hexagonal barium ferrite by heating within a temperature range of 600 to 670° C.
Implementation Method 2
hexagonal barium ferrite has a smaller magnetocrystalline anisotropy constant Ku than hexagonal strontium ferrite
Data Source
AI summary
A magnetic powder for a magnetic recording medium includes magnetic particles in which Ba in hexagonal barium ferrite is partially substituted with Sr, wherein a Dx volume represented by Dx volume (nm3) = Dxc ×π× (Dxa/2)2 is 2,200 nm3 or less, and an Sr/(Ba+Sr) molar ratio is 0.01 to 0.15. One that satisfies Ku ≥ 0.1 × [Sr/(Ba+Sr) molar ratio] + 0.13 is more preferred. For the formulas, Dxc is a crystallite diameter (nm) in a c-axis direction of a hexagonal ferrite crystal lattice, Dxa is a crystallite diameter (nm) in an a-axis direction of the same crystal lattice, π is a circular constant, and Ku is a magnetocrystalline anisotropy constant (MJ/m3). By providing the hexagonal ferrite magnetic powder formed of fine particles, an effect of improving the perpendicular squareness ratio SQ of a magnetic recording medium is large.