Perpendicular Magnetic Recording Medium Antiferromagnetic Pinning
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Solution Overview
Problem
Perpendicular magnetic recording media face issues with spike noise due to magnetic domain walls, noise from mirror-image transfer of the magnetic recording layer, and stray magnetic fields causing magnetization loss, which existing solutions have not adequately addressed.
Innovation Solution
A perpendicular magnetic recording medium is designed with a hard magnetic pinning layer having anisotropy perpendicular to the substrate surface, antiferromagnetically coupled with a soft underlayer via a nonmagnetic coupling layer, to reduce noise and improve writeability and signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a hard magnetic pinning layer is provided between the soft underlayer and the substrate to orient the magnetization of the soft underlayer in one direction, then the magnetization orientation is improved, but spike noise caused by magnetic domain walls arises at inside and outside diameters
Solution Approach 1:
An antiferromagnetic layer is introduced as an intermediary between the soft underlayer and the hard magnetic pinning layer. This antiferromagnetic layer mediates the magnetic interaction, allowing the soft underlayer to maintain uniform magnetization orientation perpendicular to the substrate surface while preventing the formation of magnetic domain walls that cause spike noise. The antiferromagnetic layer acts as a buffer that transmits the orientation constraint from the pinning layer without allowing domain wall formation in the soft underlayer.
Solution Approach 2:
The invention uses a composite structure consisting of multiple magnetic layers with different properties: the soft underlayer with perpendicular magnetization, the antiferromagnetic layer with specific magnetic anisotropy, and the hard magnetic pinning layer with strong magnetization orientation. This composite structure combines the advantages of each layer - the soft underlayer provides good writeability, the antiferromagnetic layer suppresses domain wall formation, and the hard pinning layer ensures uniform magnetization orientation, thereby eliminating spike noise while maintaining orientation stability.
2Stability of the object's composition
If an antiferromagnetic layer is used to pin magnetization through exchange coupling, then the magnetization orientation is stabilized, but a complicated and costly heat treatment process is required
Solution Approach 1:
The invention changes the material parameter of the layer between the soft underlayer and pinning layer from a normal magnetic layer to an antiferromagnetic layer. This parameter change fundamentally alters the magnetic interaction mechanism, allowing exchange coupling to occur at room temperature without requiring high-temperature heat treatment. The antiferromagnetic layer's specific magnetic properties enable strong exchange coupling with the soft underlayer and pinning layer, stabilizing magnetization orientation through a simpler, lower-cost manufacturing process.
3Stability of the object's composition
If two soft underlayers are provided and antiferromagnetically coupled together, then the magnetization orientation is improved, but a multidomain structure is formed and spike noise arises
Solution Approach 1:
Instead of directly coupling two soft underlayers, the invention introduces an antiferromagnetic layer as an intermediary between the soft underlayer and the hard magnetic pinning layer. This antiferromagnetic intermediary ensures uniform magnetization orientation perpendicular to the substrate while preventing the formation of multidomain structures. The antiferromagnetic layer's magnetic properties allow it to transmit orientation constraints effectively without allowing domain wall formation, thereby eliminating spike noise while maintaining stable magnetization orientation.
4Ease of operation
If the soft underlayer is used to concentrate magnetic flux for recording, then writeability is improved, but noise results from mirror-image transfer of the magnetic recording layer
Solution Approach 1:
The invention creates a composite magnetic structure where the soft underlayer with perpendicular magnetization is combined with an antiferromagnetic layer and a hard magnetic pinning layer. This composite structure maintains the soft underlayer's ability to concentrate magnetic flux for good writeability while the antiferromagnetic and hard magnetic layers suppress the mirror-image effect. The hard magnetic pinning layer with strong perpendicular magnetization orientation prevents the soft underlayer from developing the multidomain structure that causes mirror-image noise, thereby maintaining writeability while eliminating the harmful noise effect.
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 effectively reduces spike noise, mirror-image noise, and stray magnetic field effects, enhancing recording density, signal-to-noise ratio, and medium reliability.
Implementation Method 1
a hard magnetic pinning layer having anisotropy perpendicular to a surface of a nonmagnetic substrate on an upper portion of the soft magnetic layer, i.e., the side of the soft magnetic layer opposite to the nonmagnetic substrate, with a nonmagnetic coupling layer there between, and antiferromagnetically coupling the hard magnetic pinning layer and the soft underlayer together
Implementation Method 2
an underlayer made of a soft magnetic material that fulfils the role of concentrating magnetic flux produced by a magnetic head used when recording onto the recording layer
Implementation Method 3
a magnetic recording layer made of a hard magnetic material
Data Source
AI summary
A perpendicular magnetic recording medium composed of a nonmagnetic substrate having a surface onto which are provided a plurality of layers including, in the order recited, a soft underlayer; a nonmagnetic coupling layer; a hard magnetic pinning layer which is antiferromagnetically coupled to the soft underlayer at ambient temperature via the nonmagnetic coupling layer and which has an axis of easy magnetization which extends in a direction which is perpendicular to that of the surface of the nonmagnetic substrate; a nonmagnetic intermediate layer; and a magnetic recording layer. Such a perpendicular magnetic recording medium has an improved medium performance, with reduced noise originating from the presence of the soft underlayer, and no erasure of recorded magnetization when influenced by an external magnetic field.