Magnetic Medium with Antiparallel Coupled Layers for Thermal Stability
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Solution Overview
Problem
Three-dimensional magnetic recording faces instability in ferromagnetic resonance frequency due to stray fields from surrounding bits, affecting data storage density and thermal stability, as the reversal magnetic field increases with finer grain sizes and magnetic anisotropy.
Innovation Solution
A magnetic medium with alternating layers of hard and soft magnetic materials, where the non-magnetic layer causes antiparallel coupling between them, reducing stray field effects and maintaining thermal stability by using materials like CoCr alloy for the first layer and NiFe alloy for the second layer, with Ru as the non-magnetic layer, allowing for distinct ferromagnetic resonance frequencies and reduced reversal magnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the grain size of the magnetic medium is reduced to increase storage density, then the storage density is improved, but the thermal stability is reduced
Solution Approach 1:
The patent employs a composite magnetic layer structure consisting of a first magnetic layer (CoCr alloy with high magnetic anisotropy) and a second magnetic layer (NiFe alloy with low magnetic anisotropy) coupled through a non-magnetic Ru layer. This composite structure enables the system to achieve both high storage density and thermal stability by combining materials with complementary properties.
Solution Approach 2:
The patent applies different magnetic properties to different layers: the first magnetic layer uses CoCr alloy with high magnetic anisotropy constant (Ku1) to provide thermal stability, while the second magnetic layer uses NiFe alloy with low magnetic anisotropy constant (Ku2) to reduce the reversal magnetic field. This local differentiation of material properties resolves the contradiction between density and stability.
2Reliability
If the magnetic anisotropy is increased to maintain thermal stability with finer grains, then the thermal stability is improved, but the reversal magnetic field increases making writing difficult
Solution Approach 1:
The patent uses a composite structure where the first magnetic layer (CoCr) provides high magnetic anisotropy for thermal stability, while the second magnetic layer (NiFe) provides low magnetic anisotropy to reduce the reversal field. The alternating layers with opposite magnetization directions create a net reduction in the reversal magnetic field required for writing.
Solution Approach 2:
The second magnetic layer with low magnetic anisotropy acts as a counterweight to the high magnetic anisotropy of the first layer, reducing the overall reversal magnetic field. The alternating magnetization directions between layers create opposing magnetic fields that cancel each other out, making writing easier while maintaining thermal stability.
3Quantity of substance
If three-dimensional magnetic recording with multiple layers is used to increase storage density, then the storage density is improved, but the ferromagnetic resonance frequency becomes unstable due to stray fields
Solution Approach 1:
The alternating layers with opposite magnetization directions create stray fields that cancel each other out. The second magnetic layer's magnetization opposes the first layer's magnetization, reducing the net stray field effect on ferromagnetic resonance frequency stability in three-dimensional magnetic recording.
Solution Approach 2:
The patent changes the magnetic anisotropy parameter between layers (high Ku1 in CoCr layer, low Ku2 in NiFe layer) to achieve both stable ferromagnetic resonance frequency and reduced stray field effects, enabling reliable three-dimensional magnetic recording.
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 stabilizes the ferromagnetic resonance frequency, enabling efficient writing and reading by suppressing stray field influences and maintaining thermal stability, thus enhancing data storage density and reliability in three-dimensional magnetic recording.
Implementation Method 1
the non-magnetic layer causes magnetic exchange coupling between the first and second magnetic layers, with the magnetization directions aligned antiparallel
Implementation Method 2
the recording layer is selected by using ferromagnetic resonance when reading or writing. Since each recording layer has a different ferromagnetic resonance frequency, a desired layer can be selected when reading or writing by applying a high-frequency magnetic field which causes ferromagnetic resonance only in the desired layer
Data Source
AI summary
According to one embodiment, a magnetic medium includes at least one recording layer including a first magnetic layer, a second magnetic layer and a non-magnetic layer. The first magnetic layer is form of a first magnetic material having a first magnetic anisotropy. The second magnetic layer is made of a second magnetic material having a second magnetic anisotropy different from the first magnetic anisotropy. The non-magnetic layer is made of a non-magnetic material and between the first and second magnetic layers, the first magnetic layer and the second magnetic layer being coupled such that directions of magnetization of the first and second magnetic layers are opposed to each other.