Perpendicular Magnetic Recording Medium Layer Design
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Solution Overview
Problem
Perpendicular magnetic recording media face challenges in achieving high recording density while maintaining thermal stability and reproducing characteristics, as increased magnetic anisotropy leads to insufficient writing and deteriorated reproducing characteristics due to exchange coupling in the in-plane direction.
Innovation Solution
A perpendicular magnetic recording medium with a structure comprising a nonmagnetic substrate, a soft magnetic layer, an alignment control layer, and a magnetic recording layer composed of two layers: a first magnetic recording layer with high magneto-crystalline anisotropic energy (Ku) and a second magnetic recording layer with low Ku, along with an exchange coupling control layer, using CoCrPtRu magnetic alloy grains and oxide grain boundaries to control exchange coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the perpendicular magnetic anisotropy (Ku) is increased to reduce noise and ensure thermal stability, then thermal stability is improved, but Hc and Hc0 increase causing insufficient writing and deteriorated reproducing characteristics
Solution Approach 1:
The magnetic recording layer is divided into multiple layers with different Ku values. The first magnetic recording layer has high Ku (≥4×10^6 erg/cc) for thermal stability, while the second magnetic recording layer has low Ku (≤2×10^6 erg/cc) for easy writing. This segmentation allows each layer to fulfill different functional requirements simultaneously.
Solution Approach 2:
Different regions of the magnetic recording structure are given different magnetic properties. The first magnetic recording layer has high magnetic anisotropy for stability, while the second layer has low magnetic anisotropy for writeability. The grain boundary regions contain oxide phases that locally modify magnetic properties to achieve the desired Ku values in each layer.
2Object-generated harmful factors
If exchange coupling between magnetic crystal grains is decreased by adding SiO2 to form granular structure, then noise is reduced, but magnetic anisotropy energy must be increased which leads to insufficient writing
Solution Approach 1:
The magnetic recording layer is segmented into magnetic crystal grains separated by oxide-containing grain boundaries. This granular structure reduces magnetic interaction between grains, lowering noise while maintaining writeability through the two-layer configuration with different Ku values.
Solution Approach 2:
The magnetic recording layer uses a composite structure combining magnetic CoCrPtRu alloy grains with non-magnetic oxide grain boundaries (containing elements like Si, B, Al, Ti, Ta, W, Mo, Nb, Hf, Zr). This composite approach reduces grain-to-grain magnetic interaction and noise while the two-layer design maintains adequate writing capability.
3Quantity of substance
If recording density is increased, then areal recording density is improved, but demagnetizing field influence increases and thermal stability becomes difficult to maintain
Solution Approach 1:
The magnetic recording layer is divided into fine magnetic crystal grains (average diameter 5-15 nm) separated by grain boundaries, enabling high recording density while the perpendicular magnetic anisotropy and two-layer structure maintain thermal stability at high densities.
Solution Approach 2:
The invention changes the magnetic anisotropy parameter by creating a two-layer structure with different Ku values. The high Ku first layer provides thermal stability while the low Ku second layer enables writing, allowing high recording density to be achieved without sacrificing thermal stability.
4Object-generated harmful factors
If grain size of magnetic crystal grains is decreased to reduce noise, then noise is reduced, but maintaining thermal stability requires increased magnetic anisotropy leading to insufficient writing
Solution Approach 1:
The magnetic recording layer uses fine magnetic crystal grains (5-15 nm diameter) segmented by oxide grain boundaries to reduce noise, while the two-layer structure with different Ku values ensures that thermal stability is maintained without requiring excessive magnetic anisotropy that would prevent writing.
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 achieves excellent thermal stability and high recording density with improved recording and reproducing characteristics by modulating exchange coupling and reducing noise, ensuring effective magnetization inversion and thermal stability.
Implementation Method 1
Because of exchange coupling between a hard magnetic film as the main recording layer and a soft magnetic film as the auxiliary layer, it becomes possible to invert at a lower applied magnetic field than that of a conventional perpendicular magnetic recording medium if the auxiliary layer portion initiates magnetization inversion upon application of the magnetic field from the head first
Implementation Method 2
In the perpendicular magnetic recording system, crystal grains of a recording layer for recording information has an easy axis of magnetization in a direction perpendicular to a substrate. The easy axis of magnetization is an axis in the direction of which magnetization easily points. In the case of a conventionally used Co-based alloy, the easy axis of magnetization is an axis (c-axis) parallel to the normal line of a (002) crystal plane of a hexagonal closest-packed structure of Co. Therefore, an influence of a demagnetizing field between recording bits is small even when the recording density increases, and the magnetization is magnetostatically stable
Data Source
AI summary
The present invention relates to a perpendicular magnetic recording medium including a nonmagnetic substrate, and at least a soft magnetic layer (SUL), an alignment control layer, a magnetic recording layer and a protective layer formed on the nonmagnetic substrate, wherein the magnetic recording layer is constituted of two or more layers and includes a first magnetic recording layer and a second magnetic recording layer from the nonmagnetic substrate side and, regarding magnetocrystalline anisotropic energy Ku of each magnetic recording layer, the first magnetic recording layer has 4×106 erg/cc or higher and the second magnetic recording layer has 2×106 erg/cc or lower, wherein the first magnetic recording layer is constituted of CoCrPtRu magnetic alloy crystal grains and grain boundaries made of an oxide and the area of grain boundaries is 30% or more based on the entire area in a planar TEM observation of the first magnetic recording layer. The present invention also relates to a magnetic recording and reproducing apparatus using the perpendicular magnetic recording medium.