Heat-Assisted Magnetic Recording Medium Underlayer Design
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Solution Overview
Problem
Current heat-assisted magnetic recording media require high substrate temperatures to achieve the L10 structure for FePt or CoPt alloys, which exceeds the heat resistance limit of glass substrates, and adding third elements to reduce this temperature results in decreased magnetic anisotropy and increased coercive force dispersion.
Innovation Solution
A heat-assisted magnetic recording medium structure is developed with a substrate, underlayers of specific alloys, and a magnetic layer with a L10 structure, where the underlayers include a first amorphous or microcrystalline layer, a second BCC Cr alloy layer, a third BCC alloy layer with a lattice constant of 2.98 Å or more, and a thin MgO layer, allowing for a low ordering temperature without adding third elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the substrate temperature is increased to 600°C or higher to order FePt alloy and obtain L10 structure, then the magnetic anisotropy is improved, but the heat resistance of glass substrate is exceeded
Solution Approach 1:
A multi-layer underlayer structure is introduced as an intermediary between the substrate and FePt alloy. This underlayer includes a Cr-based BCC alloy layer and a Ru-based BCC alloy layer with specific lattice constants, which mediate the ordering process to reduce the required substrate temperature from 600°C or higher to below 600°C while still achieving the L10 structure with high magnetic anisotropy
Solution Approach 2:
The invention changes the parameters of the underlayer structure, specifically using Cr-based BCC alloy with lattice constant 2.91-2.97 Å and Ru-based BCC alloy with lattice constant 2.98 Å or more. These parameter changes in the underlayer enable the FePt alloy to be ordered at lower temperatures while maintaining high magnetic anisotropy
2Temperature
If a third element is added to FePt alloy to decrease ordering temperature, then the substrate temperature requirement is reduced, but the magnetic anisotropy decreases and coercive force dispersion increases
Solution Approach 1:
Instead of adding third elements to FePt alloy, the invention uses a Cr-based BCC alloy layer and Ru-based BCC alloy layer as intermediary underlayers. These underlayers facilitate the ordering process of FePt alloy without introducing elements that would degrade magnetic anisotropy or increase coercive force dispersion
Solution Approach 2:
The underlayer is segmented into multiple functional layers: a Cr-based BCC alloy layer (10-20 nm thick) and a Ru-based BCC alloy layer (5-15 nm thick). This segmentation allows each layer to perform specific functions in reducing ordering temperature while maintaining magnetic properties
3Stability of the object's composition
If the thickness of MgO underlayer is increased to 10 nm or more to realize favorable (100) orientation, then the orientation quality is improved, but the production efficiency decreases and particle generation increases
Solution Approach 1:
The Cr-based BCC alloy layer and Ru-based BCC alloy layer serve as intermediary layers between the substrate and MgO underlayer. These intermediaries provide the necessary lattice matching and orientation guidance, enabling the MgO underlayer to achieve favorable (100) orientation at reduced thickness of 5 nm or less, thus improving production efficiency while maintaining orientation quality
Solution Approach 2:
The invention changes the thickness parameter of the MgO underlayer from the conventional 10 nm or more to 5 nm or less. This parameter change is made possible by the presence of the Cr-based and Ru-based BCC alloy underlayers, which provide the necessary orientation guidance at reduced thickness
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 enables a high-capacity magnetic recording medium with a reduced MgO underlayer thickness of 5 nm or less, maintaining high coercive force and thermal stability while avoiding the need for high-temperature processing.
Implementation Method 1
the under layer is constituted by a first under layer made of an amorphous alloy or an alloy having a microcrystalline structure, a second under layer made of Cr or an alloy which contains Cr as a principle component and has a BCC structure, a third under layer made of a metal or an alloy having a BCC structure with a lattice constant of 2.98 Å or more, and a fourth under layer made of MgO
Implementation Method 2
the magnetic layer includes an alloy having a L10 structure as a principle component
Data Source
AI summary
The heat-assisted magnetic recording medium of the present invention has a substrate, an under layer formed on the substrate, and a magnetic layer formed on the under layer, in which the magnetic layer includes an alloy having a L10 structure as a principle component, and the under layer is constituted by a first under layer made of an amorphous alloy or an alloy having a microcrystalline structure, a second under layer made of Cr or an alloy which contains Cr as a principle component and has a BCC structure, a third under layer made of a metal or an alloy having a BCC structure with a lattice constant of 2.98 Å or more, and a fourth under layer made of MgO.