Spin Torque Oscillator Frequency Stabilization in Disk Drives
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Solution Overview
Problem
The high-frequency assisted writing method using a spin torque oscillator (STO) in disk drives faces instability due to fluctuations in the oscillation frequency caused by leakage recording magnetic fields, which hinders stable and high-quality high-density recording.
Innovation Solution
The implementation of a disk drive with a spin torque oscillator that stabilizes its oscillation frequency through specific configurations, such as adjusting the drive current in response to changes in the leakage recording magnetic field, and using a multi-layer structure with a spin injection layer, non-magnetic layer, and oscillation layer to maintain consistent high-frequency magnetic field application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spin torque oscillator (STO) is used as the source of high-frequency magnetic field, then the coercive force reduction effect is enhanced, but the oscillation frequency becomes unstable due to leakage recording magnetic fields
Solution Approach 1:
The patent applies feedback control by detecting the oscillation frequency of the STO and adjusting the drive current accordingly. The frequency detection unit monitors the oscillation frequency, and the drive current adjustment unit modifies the drive current to maintain the oscillation frequency within a predetermined range, thereby compensating for frequency drifts caused by leakage recording magnetic fields.
Solution Approach 2:
The patent changes the drive current parameter dynamically to stabilize the oscillation frequency. By adjusting the drive current based on detected frequency deviations, the system maintains stable STO operation despite variations in leakage recording magnetic fields, ensuring consistent high-frequency magnetic field generation.
2Manufacturing precision
If the STO is arranged near the recording pole to apply high-frequency magnetic field to the recording part, then the recording density is increased, but the oscillation frequency fluctuates due to leakage recording magnetic fields
Solution Approach 1:
The patent uses feedback control where the frequency detection unit continuously monitors the STO oscillation frequency and the drive current adjustment unit modifies the drive current to maintain frequency stability. This feedback mechanism compensates for frequency fluctuations caused by the STO's proximity to the recording pole and leakage magnetic fields.
Solution Approach 2:
The patent replaces mechanical adjustment methods with electrical control by using current adjustment to stabilize frequency. Instead of physically repositioning the STO or recording pole, the system uses electrical feedback to maintain optimal oscillation frequency, enabling precise control without mechanical complexity.
3Power
If the drive current is increased to maintain oscillation frequency, then the high-frequency magnetic field strength is enhanced, but power consumption increases
Solution Approach 1:
The feedback control system adjusts the drive current only as much as necessary to maintain oscillation frequency within the predetermined range. This prevents excessive current increase and associated power consumption while still ensuring sufficient high-frequency magnetic field strength for effective recording.
Solution Approach 2:
The patent uses dynamic current adjustment based on real-time frequency detection. The drive current is continuously optimized to match the actual oscillation conditions, preventing both insufficient field strength and unnecessary power consumption. This dynamic optimization balances performance and energy 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 approach enables stable, high-quality, high-density recording by ensuring the oscillation frequency of the STO remains constant despite changes in the recording magnetic field, thereby maintaining the coercive force reduction and achieving reliable data writing.
Implementation Method 1
The stream of the electrons thus polarized exerts a spin torque to the oscillation layer, magnetizing the oscillation layer. Thus magnetized, the oscillation layer undergoes ferromagnetic resonance, generating a high-frequency magnetic field.
Implementation Method 2
When a current is supplied to the STO, the spin of the electrons passing through the spin-injection layer is polarized.
Implementation Method 3
This method is a technique of applying a magnetic field of a frequency much higher than the recording-signal frequency to a prescribed tiny part of a magnetic disk, thereby reducing the coercive force that part has in the recording-signal frequency region
Data Source
AI summary
According to one embodiment, a disk drive having a spin torque oscillator and designed to perform high frequency assisted writing. The disk drive has a magnetic disk, a magnetic head, a coil, and a drive current controller. The drive current controller controls a drive current to supply to the spin torque oscillator. To record data magnetically in the disk, the drive current controller supplies to the spin torque oscillator the drive current that changes in synchronism with the polarity inversion of the recording current supplied to the coil, which excites the recording magnetic pole of the magnetic head.