Thermally-Assisted Magnetic Recording Head Near-Field Optical Device
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Solution Overview
Problem
In magnetic recording systems, the decrease in magnetic grain size for higher recording densities leads to thermal stability issues due to increased anisotropic magnetic fields, making it difficult to write data when the coercive force exceeds the write field limit, and existing near-field optical systems face challenges in light use efficiency and thermal management.
Innovation Solution
A thermally-assisted magnetic recording head is designed with a waveguide, a near-field optical device configured to emit NF-light from a surface plasmon generator, and a magnetic pole, where the NF-light generation point is positioned close to the magnetic pole without the waveguide in between, using a triangular-shaped NF-optical device with a specific vertex angle and rounded propagation edge, and covered with a material of lower refractive index, arranged in a Kretschmann configuration to enhance light coupling and reduce thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If magnetic grain size is decreased to increase recording density, then recording density is improved, but thermal stability of magnetization deteriorates due to decreased volume
Solution Approach 1:
The patent changes the magnetic anisotropy energy parameter (KU) by selecting specific magnetic materials and controlling their microstructure. By increasing magnetic anisotropy energy through material composition control and grain structure optimization, the patent achieves both high recording density and thermal stability, resolving the contradiction between these two parameters.
2Reliability
If magnetic anisotropy energy KU is increased to improve thermal stability, then thermal stability is improved, but anisotropic magnetic field (coercive force) increases, making writing difficult when it exceeds the write field limit
Solution Approach 1:
The patent applies preliminary heating to the magnetic recording medium before writing operations. By pre-heating the medium to reduce its coercive force, the patent enables successful writing even for high-anisotropy materials that would otherwise be difficult to write. This preliminary thermal action resolves the contradiction between thermal stability and writeability.
Solution Approach 2:
The patent employs periodic pulsed heating combined with write field application. The heating pulse is applied just before and during the write operation, creating a time-dependent process where the medium's coercive force is temporarily reduced during the critical writing window, then returns to high stability afterward. This periodic action resolves the contradiction between ease of writing and thermal stability.
3Productivity
If laser light is directly applied to NF-optical device to generate NF-light, then NF-light generation efficiency is improved, but temperature of NF-optical device excessively rises, causing thermal expansion that increases distance from magnetic recording medium
Solution Approach 1:
The patent introduces a waveguide as an intermediary component between the laser light source and the NF-optical device. The waveguide delivers laser light to excite surface plasmons in the NF-optical device indirectly, rather than direct illumination. This intermediary approach maintains efficient NF-light generation while preventing excessive temperature rise in the NF-optical device, resolving the contradiction between generation efficiency and thermal management.
4Ease of operation
If NF-optical device is positioned close to magnetic pole to improve write field gradient, then write field gradient is improved, but light use efficiency deteriorates due to absorption by magnetic pole
Solution Approach 1:
The patent applies local quality differentiation by using a waveguide structure that confines and directs light propagation to specific regions. The waveguide delivers light precisely to the NF-optical device location near the magnetic pole, ensuring high write field gradient where needed while preventing light absorption by the magnetic pole in other regions. This spatially selective light delivery resolves the contradiction between write field gradient and light use efficiency.
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 efficient generation and application of NF-light close to the magnetic pole, improving write field gradients and thermal management, enabling reliable thermally-assisted magnetic recording with high recording density and reduced light absorption, thus overcoming the limitations of existing systems.
Implementation Method 1
a waveguide for transmitting a light to be applied to a near-field optical device
Implementation Method 2
a near-field optical device configured to convert the light into surface plasmons and to generate near-field light from surface plasmons
Implementation Method 3
by matching the frequency of the light with the resonant frequency of plasmon excited in the metal
Implementation Method 4
there can also be avoided a situation in which the light use efficiency of a NFL-generating optical system including a NF-optical device is degraded because thermal fluctuation of free electrons increases in the NF light generator
Implementation Method 5
arranged in a Kretschmann configuration to enhance light coupling
Data Source
AI summary
There is provided a near-field-light (NFL) generating optical system in which the point where near-field (NF) light is generated can be provided sufficiently close to the end surface of a magnetic pole that generates write field. The optical system comprises: a waveguide through which a light for exciting surface plasmon propagates; and a NF-optical device configured to be coupled with the light in a surface plasmon mode. The NF-optical device comprises: a contact-to-waveguide surface having a contact to the waveguide; and a propagation edge provided on the side opposite to the contact-to-waveguide surface, extending to the NFL-generating end surface of the device, and configured to propagate thereon the surface plasmon excited by the light. In this optical system, the point, where NF-light is generated, of the NFL-generating end surface is reliably located on the side opposite to the waveguide.