Inverted-Trapezoidal Waveguide for TMR Head Light Coupling
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Solution Overview
Problem
In thermally-assisted magnetic recording, the decrease in magnetic grain size for higher recording densities leads to degradation in thermal stability and increased anisotropic magnetic fields, making it difficult to write data when the coercive force exceeds the write field limit.
Innovation Solution
A thermally-assisted magnetic recording head with a waveguide and near-field optical device configured in a surface plasmon mode, where the waveguide has a trapezoidal cross-section to enhance light use efficiency, allowing for effective coupling and intense near-field light generation at the magnetic pole side, reducing the anisotropic magnetic field and enabling writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the size of magnetic grains is decreased to improve recording density, then recording density is improved, but thermal stability of magnetization is degraded
Solution Approach 1:
The patent changes the magnetic anisotropy energy parameter (KU) by selecting specific magnetic materials and controlling their microstructure. By increasing KU through material composition control and grain structure optimization, the patent achieves both high recording density and sufficient thermal stability, resolving the contradiction between grain size reduction and thermal stability maintenance.
2Stability of the object's composition
If the magnetic anisotropy energy KU is increased to improve thermal stability, then thermal stability is improved, but anisotropic magnetic field (coercive force) increases
Solution Approach 1:
The patent optimizes the magnetic anisotropy energy parameter KU to a specific range that balances thermal stability and writability. By controlling KU through material selection and microstructure control, the patent achieves sufficient thermal stability while keeping the anisotropic magnetic field within the write field limit of the head, resolving the contradiction between thermal stability and coercive force.
3Use of energy by moving object
If the light use efficiency is improved by optimizing waveguide coupling, then light use efficiency is improved, but device complexity increases
Solution Approach 1:
The patent employs an inverted trapezoidal waveguide cross-section with asymmetric geometry. This asymmetric structure optimizes the coupling between the waveguide and the near-field optical device, improving light use efficiency by directing evanescent light effectively to the plasmon excitation region without requiring complex additional components.
Solution Approach 2:
The patent utilizes the evanescent field dimension by designing the waveguide to allow light to seep from its side surface. This dimensional approach enables coupling with the near-field optical device through the evanescent field, improving light use efficiency without adding complex mechanical or optical components.
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 solution improves light use efficiency and allows for reliable thermally-assisted magnetic recording by generating intense near-field light, enabling data writing even when the anisotropic magnetic field is high, thus addressing the thermal stability and coercive force issues.
Implementation Method 1
a near-field (NF-) optical device configured to be coupled with the light in a surface plasmon mode and to emit near-field light (NF-light)
Implementation Method 2
a surface plasmon mode is induced in the portion by coupling between evanescent light that is equivalent to waveguide light seeping from the waveguide and fluctuations in charge excited on the surface of the surface plasmon generator
Implementation Method 3
laser light is coupled with the NF-optical device in a surface plasmon mode to cause excited surface plasmon to propagate to the opposed-to-medium surface, thereby providing NF-light
Implementation Method 4
cause excited surface plasmon to propagate to the opposed-to-medium surface
Implementation Method 5
light seeping from the waveguide
Implementation Method 6
a magnetic recording medium formed of a magnetic material with a large magnetic anisotropy energy KU is used so as to stabilize the magnetization; anisotropic magnetic field of the medium is reduced by applying heat to a portion of the medium where data is to be written
Data Source
AI summary
Provided is a thermally-assisted magnetic recording head comprising a near-field-light-generating (NFL-generating) optical system with an improved light use efficiency. The head comprises a magnetic pole, a waveguide propagating a light for exciting surface plasmon, and a NF-optical device configured to emit NF-light from its end surface located adjacent to the magnetic pole end surface. The waveguide cross-section, taken by a plane perpendicular to a waveguide edge along elongated direction, has substantially a trapezoidal shape in which a longer side of opposed parallel sides is an edge of the cross-section on the NF-optical device side. This configuration enables a coupled portion of the NF-optical device which is coupled with the light to be placed in the effective distribution range of the light seeping from the waveguide. Consequently, there can be realized a sufficiently strong coupling between the light seeping from the waveguide and the NF-optical device.