FePt Magnetic Recording Media Grain Size Control
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Solution Overview
Problem
Conventional magnetic recording media face limitations in achieving high areal densities due to thermal instabilities and super-paramagnetism issues with small grain sizes, necessitating higher magnetic anisotropy and thermal stability, which is challenging with existing materials and recording techniques.
Innovation Solution
A magnetic recording medium with a substrate-supported iron-platinum (FePt) layer having a granular configuration with predominantly L10 crystal structure, average grain size between 2 nm and 10 nm, perpendicular magnetization orientation, and boron interspersed among the grains, along with an underlayer to control grain size, enabling high coercivity and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional cobalt-alloy media are used to increase areal density, then recording density can be improved, but thermal stability deteriorates due to super-paramagnetism in small grains
Solution Approach 1:
The patent changes the magnetic material composition from conventional cobalt-alloy to L10-ordered FePt alloy, which has significantly higher magnetocrystalline anisotropy energy (Ku ≈ 7×10^7 ergs/cc). This parameter change in material composition enables thermal stability at smaller grain sizes required for high areal density recording
Solution Approach 2:
The patent uses a composite thin film structure consisting of multiple layers including FePt magnetic recording layer, Ru underlayer, and various buffer layers. This composite structure combines materials with different properties to achieve both high anisotropy and controlled grain morphology for thermal stability
2Productivity
If grain size is reduced to increase areal density, then storage capacity is improved, but thermal stability deteriorates due to super-paramagnetism
Solution Approach 1:
The patent changes the magnetic material from cobalt-alloy to L10-ordered FePt with higher Ku value, which maintains thermal stability even when grain size is reduced to 5-15 nm for high areal density recording
Solution Approach 2:
The patent applies preliminary actions during film deposition including using Ru underlayer to control grain nucleation, controlling deposition temperature (200-400°C), and using specific deposition rates to pre-establish grain size and morphology before final magnetic recording layer formation
3Reliability
If magnetic anisotropy is increased to maintain thermal stability, then thermal stability is improved, but ease of operation deteriorates due to limited head field capability
Solution Approach 1:
The patent utilizes phase transition concepts by depositing the FePt layer in a disordered phase initially, then applying in-situ heat treatment (200-400°C) during deposition to induce L10 ordering. This controlled phase transition enables high anisotropy development while maintaining grain size control through the Ru underlayer
Solution Approach 2:
The Ru underlayer performs preliminary action by controlling grain nucleation and growth during deposition, pre-establishing the grain size and morphology before the FePt layer develops its high anisotropy, thus enabling both thermal stability and writeability
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 solution achieves high-density magnetic storage beyond 1 Tbit/in2 by ensuring thermal stability and magnetic isolation of grains, enhancing coercivity and storage density while maintaining signal-to-noise ratio.
Implementation Method 1
L10 iron-platinum (FePt), which has a high bulk magnetocrystalline anisotropy energy constant Ku of ̃7×107 ergs/cc
Implementation Method 2
a magnetization orientation substantially perpendicular to the surface of the substrate
Implementation Method 3
boron interspersed among the grains, wherein the boron comprises about 5% to about 40% of the magnetically recordable layer, by volume
Data Source
AI summary
Iron-platinum (FePt) based magnetic recording media structures that provide small grain size and isolated-grain configurations suitable for high-density magnetic recording. In one of the structures, the recording media structure includes a thin film containing grains of L10 FePt and boron as a segregant contained in intergranular regions located among the FePt grains. In another structure, the recording media structure includes a thin film containing grains of L10 FePt, wherein the film is formed on an underlayer containing at least one material selected to control the size of the FePt grains in the film. Proper choices of materials, relative amounts of the materials, processing parameters, and other variables permit these structures to be formed with grain sizes, magnetization orientations, and perpendicular coercivities that allow designers to create magnetic storage devices having storage densities of 1 Tbit/in2 and greater.