Perpendicular Magnetic Recording Medium with Nitrogen-Doped Soft Layer
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Solution Overview
Problem
Existing perpendicular magnetic recording media face challenges in achieving a balance between thermal stabilization of magnetization, signal-to-noise ratio (SNR) improvement, and ease of writing by the magnetic head, as high recording density demands require a tradeoff between these factors, with previous solutions either neglecting ease of writing or not adequately controlling the physical properties of the magnetic recording layers.
Innovation Solution
A perpendicular magnetic recording medium is developed with a magnetic recording layer comprising a low Ku layer with a soft magnetic thin film having an iron-group-element based microcrystal structure, including nitrogen, and a high Ku layer with a hexagonal close-packed crystal structure, where the crystal grain size and saturation magnetization are controlled to enhance thermal stabilization, writing ease, and SNR, by adjusting the nitrogen content and layer configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Ku value of the magnetic recording layer is increased to improve thermal stabilization of magnetization, then thermal stability is improved, but the magnetic field necessary for magnetization reversal becomes excessively high, making writing by magnetic head difficult
Solution Approach 1:
The magnetic recording layer is divided into multiple sub-layers with different Ku values. The lower sub-layer has a lower Ku value to facilitate magnetization reversal during writing, while the upper sub-layer has a higher Ku value to provide thermal stability. This segmentation allows each sub-layer to fulfill its specific function, resolving the contradiction between thermal stability and ease of writing.
Solution Approach 2:
Different regions of the magnetic recording layer are assigned different magnetic properties. The lower sub-layer is designed with lower perpendicular magnetic anisotropy to enable easy magnetization reversal, while the upper sub-layer is designed with higher perpendicular magnetic anisotropy to maintain thermal stability. This local differentiation of properties allows the system to simultaneously achieve both thermal stability and ease of writing.
2Loss of information
If the crystal grain size of the magnetic recording layer is reduced to improve signal-to-noise ratio, then SNR is improved, but the volume of magnetic grains decreases, requiring higher Ku value to maintain energy barrier against thermal fluctuation
Solution Approach 1:
The magnetic recording layer is segmented into multiple sub-layers, where the cumulative volume of magnetic grains across all sub-layers provides sufficient energy barrier against thermal fluctuation, while individual grains in each sub-layer can be kept small to reduce noise. This allows small grain size for high SNR while maintaining adequate total volume for thermal stability.
Solution Approach 2:
The magnetic recording layer is constructed as a composite structure with multiple sub-layers having different magnetic properties. This composite structure enables the system to achieve both high SNR (through small grain size in each layer) and sufficient thermal stability (through the combined effect of multiple layers with appropriate Ku values).
3Loss of information
If the magnetic interactions between crystal grains are reduced to improve SNR, then SNR is improved, but the coercive force becomes closer to the anisotropy field, requiring even higher magnetic field for magnetization reversal
Solution Approach 1:
The magnetic recording layer is divided into multiple sub-layers with different magnetic properties. In the lower sub-layer, moderate magnetic interactions are maintained to allow easier magnetization reversal, while in the upper sub-layer, magnetic interactions are reduced to improve SNR. This segmentation allows optimization of both SNR and ease of writing in different regions.
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 allows for stable production of the soft magnetic layer with improved thermal stabilization, ease of writing, and enhanced SNR, effectively addressing the tradeoff between these factors by controlling the physical properties of the magnetic recording layers, particularly through the use of nitrogen addition and specific crystal orientations.
Implementation Method 1
the thin film having a crystal structure of a face-centered cubic lattice or hexagonal close packed
Implementation Method 2
in which a nitrogen element is added to a ferromagnetic material mainly containing one of the metals of Co, Ni and Fe
Implementation Method 3
a magnetic recording layer used for the perpendicular magnetic recording medium is required to have a high perpendicular magnetic anisotropy coefficient (Ku value)
Implementation Method 4
When the energy barrier E is not sufficiently high compared with thermal energy kBT, magnetization is reversed due to an effect of the thermal energy. This is called thermal fluctuation (or thermal disturbance) of magnetization
Data Source
AI summary
A perpendicular magnetic recording medium is disclosed in which a soft magnetic layer used as a low Ku layer can be stably produced with high performance. Thermal stabilization of magnetization, ease of writing by a magnetic head, and SNR also are improved. A method of manufacturing the medium is disclosed. The perpendicular magnetic recording medium includes at least a nonmagnetic underlayer, a magnetic recording layer, and a protective layer formed in this order on a nonmagnetic substrate. The magnetic recording layer includes a low Ku layer having a relatively small perpendicular magnetic anisotropy constant (Ku value), and a high Ku layer in which the Ku value is relatively large, and the low Ku layer includes a soft magnetic thin film including an iron group element-based microcrystal structure, in which a nitrogen element is added to a ferromagnetic material mainly containing one of metals of Co, Ni and Fe or an alloy of the metal. The thin film has a crystal structure of a face-centered cubic lattice or hexagonal close packed, and a preferred crystal orientation plane parallel to a plane of the film is a (111) plane in the face-centered cubic lattice structure, and a (002) plane in the hexagonal close packed structure.