Perpendicular Magnetic Recording Medium Layered Structure
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Solution Overview
Problem
Perpendicular magnetic recording media face a trade-off between improving signal-to-noise ratio (SNR), thermal stability of magnetization, and ease of writing with a magnetic head, as high Ku values enhance thermal stability but increase the magnetic field required for magnetization reversal, making it difficult to simultaneously achieve all three factors.
Innovation Solution
A two-layer magnetic recording medium structure with a low Ku layer and a high Ku layer, where the low Ku layer has a perpendicular magnetic anisotropy constant of not more than 1×105 erg/cm3 and the high Ku layer has a constant of at least 1×106 erg/cm3, allowing for magnetic coupling in the thickness direction to facilitate magnetization reversal and reduce the energy barrier, thereby improving thermal stability and writing ease.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the perpendicular magnetic anisotropy constant (Ku value) is increased to improve thermal stability of magnetization, then thermal stability is improved, but the magnetic field required for magnetization reversal increases, making writing with a magnetic head difficult
Solution Approach 1:
The magnetic recording layer is divided into two distinct layers: a first magnetic recording layer with high perpendicular magnetic anisotropy (Ku≥1×10^6 erg/cm³) and a second magnetic recording layer with low perpendicular magnetic anisotropy (Ku≤1×10^5 erg/cm³). This segmentation allows each layer to fulfill different functions - the first layer provides thermal stability while the second layer facilitates easy magnetization reversal during writing operations.
Solution Approach 2:
Different regions of the magnetic recording layer are assigned different Ku values to optimize local properties. The first layer (with high Ku) is positioned to provide thermal stability where needed, while the second layer (with low Ku) is positioned to enable easy writing. This local differentiation of magnetic properties resolves the contradiction between thermal stability and writing ease.
2Reliability
If the perpendicular magnetic anisotropy constant (Ku value) is increased to improve thermal stability, then thermal stability is improved, but the signal-to-noise ratio (SNR) deteriorates due to increased medium noise
Solution Approach 1:
The magnetic recording layer is segmented into two layers with different Ku values. The second layer with low Ku (≤1×10^5 erg/cm³) reduces magnetic interactions between grains and minimizes reverse magnetic domain noise, thereby improving SNR. Simultaneously, the first layer with high Ku (≥1×10^6 erg/cm³) ensures sufficient thermal stability, resolving the contradiction between thermal stability and SNR.
3Loss of information
If the crystal grain diameter is reduced to improve signal-to-noise ratio, then SNR is improved, but the energy barrier for magnetization reversal decreases, compromising thermal stability
Solution Approach 1:
The magnetic recording layer is divided into two layers with different Ku values. The first layer with high Ku (≥1×10^6 erg/cm³) compensates for the reduced grain size by providing sufficient perpendicular magnetic anisotropy to maintain thermal stability. The second layer with low Ku (≤1×10^5 erg/cm³) allows for smaller grain diameters that improve SNR. This layered structure enables small grain sizes without sacrificing thermal stability.
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 two-layer structure enhances thermal stability and ease of writing with a magnetic head, while maintaining a high signal-to-noise ratio, as evidenced by improved overwrite characteristics and reduced magnetic field requirements.
Implementation Method 1
magnetic coupling in the thickness direction to facilitate magnetization reversal
Implementation Method 2
the magnetization must be stably maintained in the direction perpendicular to the film plane. The magnetic recording layer used in such a perpendicular magnetic recording medium is thus required to have a high perpendicular magnetic anisotropy constant (Ku value)
Implementation Method 3
writing can be carried out sufficiently even with a recording medium having a high coercivity
Data Source
AI summary
There is provided a perpendicular magnetic recording medium according to which both the thermal stability of the magnetization is good and writing with a magnetic head is easy, and moreover the SNR is improved. In the case of a perpendicular magnetic recording medium comprising a nonmagnetic substrate 1, and at least a nonmagnetic underlayer 2, a magnetic recording layer 3 and a protective layer 4 formed in this order on the nonmagnetic substrate 1, the magnetic recording layer 3 comprises a low Ku region 31 layer having a perpendicular magnetic anisotropy constant (Ku value) of not more than 1×105 erg/cm3, and a high Ku region 32 layer having a Ku value of at least 1×106 erg/cm3. Moreover, the magnetic recording layer 3 is made to have therein nonmagnetic grain boundaries that contain a nonmagnetic oxide and magnetically isolate crystal grains, which are made of a ferromagnetic metal, from one another.