Thermally Assisted Magnetic Head Slider Protrusion Detection
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Solution Overview
Problem
Conventional methods fail to accurately detect the protrusion height of a second protrusion on the air bearing surface of thermally-assisted magnetic head sliders, which is crucial for maintaining the distance between the magnetic head slider and the recording medium, due to excessive thermal expansion caused by the plasmon generator, leading to potential contact and damage.
Innovation Solution
A method involving a near-field light generator that uses laser light to thermally expand the magnetic head slider, generating a first protrusion and a second protrusion, where the protrusion height is determined by establishing relationships between the spacing, heater power, and residual magnetization, allowing for precise detection when the second protrusion contacts the recording medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If heater power is increased to reduce the distance from the magnetic recording part to the recording medium, then the distance is diminished and recording density is improved, but thermal expansion becomes excessively large causing the air bearing surface to contact the recording medium
Solution Approach 1:
The patent replaces direct mechanical measurement of the air bearing surface with optical measurement using a laser beam. The laser beam reflects off the air bearing surface and the reflection position changes according to the protrusion height, allowing non-contact measurement of the thermal expansion without mechanical interference
Solution Approach 2:
The patent introduces a laser beam as an intermediary to measure the protrusion height of the air bearing surface. The laser beam reflects off the air bearing surface and the reflection position on a screen indicates the height, providing an indirect but accurate measurement method that doesn't interfere with the thermal expansion process
2Quantity of substance
If the magnetic microparticles are reduced in size to increase recording density, then recording density is improved, but thermal stability is deteriorated
Solution Approach 1:
The patent changes the physical state of the recording medium by heating it with near-field light during the recording process. This temporary parameter change (temperature increase) reduces the coercive force of the magnetic microparticles, allowing information to be recorded even when the particles are small and have high thermal stability requirements
Solution Approach 2:
The patent utilizes a temporary phase transition in the magnetic properties of the recording medium by heating it to the Curie temperature or near-Curie temperature. At this temperature, the magnetic anisotropy energy is reduced, allowing magnetic domains to be easily switched for recording, and then cools down to stabilize the recorded information
3Power
If near-field light is used to reduce coercive force for recording, then recording is enabled, but the plasmon generator is heated causing large thermal expansion and additional protrusion
Solution Approach 1:
The patent segments the thermal expansion into two distinct components: the first protrusion from the heater and the second protrusion from the plasmon generator. By separately measuring and analyzing these two protrusions, the patent can accurately determine the air bearing surface height despite the combined thermal expansion effects
Solution Approach 2:
The patent uses feedback from the laser reflection measurement to detect the actual protrusion height of the air bearing surface. This feedback information is used to adjust the heater power and plasmon generator operation to maintain the air bearing surface at the optimal height, preventing contact with the recording medium
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
Enables accurate detection of the protrusion height, preventing contact and ensuring the reliability and longevity of hard disk devices by maintaining an optimal distance between the magnetic head slider and the recording medium.
Implementation Method 1
the heater is disposed near a magnetic recording part and a reproducing part of the magnetic head slider and expands the magnetic head slider by generating heat
Implementation Method 2
The plasmon generator disposed along the core couples in a surface plasmon mode with propagation light propagating through the core at a portion opposing the core to generate surface plasmon
Implementation Method 3
The generated surface plasmon propagates to an end part of the plasmon generator to generate near-field light on the air bearing surface. The coercive force of the recording medium is decreased by heating with the near-field light
Data Source
AI summary
A magnetic head slider includes a near-field light generator, an incorporated heater is activated to thermally-expand the magnetic head slider so that a first protrusion is generated on the air bearing surface, and a second protrusion protruding from the first protrusion is generated by a thermal expansion of the near-field light generator. A standard signal is written to a recording medium with a predetermined magnetization. A relation between a residual magnetization of the standard signal and a power of the heater is obtained by lowering the magnetization of the standard signal by heating the recording medium with the near-field light while light output of laser light is maintained to be constant and the power of the heater is varied. Further, a relation between the first spacing and the residual magnetization is obtained. A value of the first spacing is obtained as a protrusion height of the second protrusion from the first protrusion when the second protrusion contacts the recording medium, the value of the first spacing being determined where an absolute value of a change rate of the residual magnetization is less than a predetermined standard value.