HAMR Disk Drive with Multiple Magnetic Recording Layers
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Solution Overview
Problem
Conventional magnetic recording hard disk drives face thermal instability issues due to the high magneto-crystalline anisotropy required for data retention, which increases coercivity beyond the write field capability, necessitating heat-assisted magnetic recording (HAMR) to maintain data integrity at ambient temperatures.
Innovation Solution
A HAMR disk drive with multiple independent continuous non-patterned magnetic recording layers, where a first data stream is written in both layers at a higher laser power level to near or above the Curie temperature, and a second data stream is written in the upper layer at a lower power level, allowing asynchronous and independent data storage without altering the magnetized regions of the lower layer, using a joint Viterbi detector to decode the composite readback signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high magneto-crystalline anisotropy (Ku) is used to ensure thermal stability of stored magnetization, then data retention is improved, but coercivity increases beyond the write field capability of the write head
Solution Approach 1:
The patent changes the temperature parameter during the writing process. By heating the recording layer to near or above its Curie temperature, the coercivity is temporarily reduced to allow the write head to magnetize the high-Ku material. After writing, the layer cools and the high coercivity is restored for thermal stability.
Solution Approach 2:
The writing process employs periodic heating cycles where the recording layer is repeatedly heated to Curie temperature and then allowed to cool. This periodic thermal action enables multiple write operations on high-Ku material that would otherwise be unwritable at room temperature.
2Quantity of substance
If multiple independent continuous magnetic recording layers are used to increase data density, then storage capacity is improved, but the complexity of writing and reading independent data streams increases
Solution Approach 1:
The patent applies local quality by using different laser power levels for different recording layers. The higher power level heats both layers for writing the first data stream, while the lower power level heats only the upper layer for writing the second data stream. This localized thermal control enables independent data writing in multiple layers.
Solution Approach 2:
The system dynamically adjusts laser power levels based on which data stream is being written. The laser power is modulated between high and low levels to selectively heat different layers, enabling flexible and independent data writing operations in multiple recording layers.
3Quantity of substance
If the upper layer is heated to near or above Curie temperature for writing the second data stream, then independent data storage is achieved, but the lower layer may be altered if heated simultaneously
Solution Approach 1:
The patent changes the laser power parameter to different levels for different writing operations. By using a lower power level for writing the second data stream in the upper layer, the heating is confined to only the upper layer, preventing alteration of the lower layer's magnetized regions while still achieving independent data storage.
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 approach ensures high thermal stability and independent data storage in multiple layers, enabling increased data density and efficient readback of asynchronous data streams, while maintaining the integrity of previously recorded data.
Implementation Method 1
the magnetic material in each data layer to near or above its Curie temperature
Implementation Method 2
heating to near or above its Curie temperature, i.e., the temperature above which the material becomes paramagnetic
Implementation Method 3
A "near-field" transducer refers to "near-field optics", wherein the passage of light is through an element with sub-wavelength features and the light is coupled to a second element
Implementation Method 4
Resonant charge motion can occur by adjusting the E-antenna dimensions to match a surface plasmon frequency to the incident light frequency
Implementation Method 5
Sometimes the metal structure of the NFT can create resonant charge motion (surface plasmons) to further increase intensity and disk heating
Implementation Method 6
The magnetic write pole is then used to change the magnetization of the recording layer while it cools
Implementation Method 7
The recorded data is then read back at ambient temperature by a conventional magnetoresistive read head
Data Source
AI summary
A heat-assisted magnetic recording (HAMR) disk drive has a disk with at least two independent data layers (RL1 and RL2), each data layer storing an independent data stream. At a high laser power both RL1 and RL2 are heated to above their respective Curie temperatures and a first data stream is recorded in both RL1 and RL2. At a lower laser power only upper RL2 is heated to above its Curie temperature and a second data stream is recorded only in RL2. The data layers are separated by a nonmagnetic spacer layer (SL) that prevents lower RL1 from being heated to above its Curie temperature at low laser power. The first and second data streams are typically asynchronous. Recorded data is read back from both data streams simultaneously as a composite readback signal. A joint Viterbi detector detects the asynchronous data streams simultaneously from the composite readback signal.