Spin Torque Oscillator Frequency Stabilization in Magnetic Disk Devices

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Solution Overview

Problem

The high-frequency assist recording system in magnetic disk devices faces instability due to variations in the oscillation frequency of the spin torque oscillator, which affects the stability of the high-frequency magnetic field applied to the magnetic disk, leading to challenges in achieving reliable high-density data recording.

Innovation Solution

A magnetic disk device with a system that includes a recording magnetic pole, a spin torque oscillator, and a coil, where a detector compares the write signal data pattern with preset patterns to adjust the STO drive current, ensuring the spin torque oscillator maintains a stable oscillation frequency by varying the STO drive current in synchronism with the write signal, thereby stabilizing the high-frequency assist recording process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a spin torque oscillator is used to generate high-frequency magnetic field for assist recording, then recording density and capacity are improved, but oscillation frequency varies due to leak recording magnetic field, causing instability

Engineering Contradiction:

Improverecording densityVSAvoidstability of high-frequency assist recording

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent introduces a feedback mechanism where the oscillation frequency of the spin torque oscillator is detected and used to adjust the drive current. The frequency detection unit monitors the oscillation frequency, and when deviation from the target frequency is detected, the drive current is adjusted accordingly to restore the oscillation frequency, thereby stabilizing the high-frequency assist recording process

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the drive current parameter of the spin torque oscillator based on detected oscillation frequency deviations. By dynamically adjusting the drive current in response to frequency variations caused by leak recording magnetic fields, the system maintains stable oscillation frequency and reliable high-density recording

Inventive Principle:

Principle #35Parameter changes

2Speed

If the spin torque oscillator is positioned near the recording magnetic pole, then high-frequency magnetic field application is achieved, but the oscillation frequency varies due to exposure to leak recording magnetic field

Engineering Contradiction:

Improveoscillation frequencyVSAvoidstability of oscillation frequency

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent implements a feedback control system where the oscillation frequency is continuously monitored and the drive current is adjusted in response to detected frequency deviations. This feedback mechanism compensates for the influence of leak recording magnetic fields on the oscillation frequency, maintaining stable operation despite the oscillator's proximity to the recording magnetic pole

Inventive Principle:

Principle #23Feedback

3Reliability

If drive current is increased to stabilize oscillation frequency, then frequency stability is improved, but energy consumption increases

Engineering Contradiction:

Improvestability of oscillation frequencyVSAvoidenergy consumption of spin torque oscillator

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent employs dynamic adjustment of the drive current based on real-time oscillation frequency detection. Rather than using a constantly high drive current, the system adjusts the current dynamically - increasing it only when frequency deviation is detected and reducing it when stability is achieved. This dynamic approach maintains frequency stability while minimizing energy consumption compared to a constantly high-current approach

Inventive Principle:

Principle #15Dynamics

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 stable high-frequency assist recording by maintaining consistent oscillation frequency of the spin torque oscillator, enhancing data recording reliability and density.

Implementation Method 1

a spin torque oscillator having an oscillation layer that oscillates when a current is supplied thereto. In these magnetic disk devices, a high-frequency magnetic field generated by the oscillation layer that has oscillated when a current is supplied to the spin torque oscillator is applied to a particular minute portion of the magnetic disk to reduce the coercive force of this portion

Methodology Applied

Scientific EffectSpin torque oscillator effect:

Implementation Method 2

a recording magnetic pole (main pole) that generates a magnetic field when a recording current is applied thereto

Methodology Applied

Scientific EffectElectromagnetic field generation: Electromagnet

Data Source

PatentUS9870789B2Magnetic disk device and high-frequency assist recording method

Publication Date: 2018.01.16 KK TOSHIBA

AI summary

According to one embodiment, a magnetic disk device includes a magnetic recording medium, a head including a recording magnetic pole, a spin torque oscillator provided near the recording magnetic pole, and a coil which excites the recording magnetic pole, a first current supply which supplies the coil with a first current corresponding to write data, a detector which detects a first signal corresponding to the write data, and outputs a second signal in accordance with the first signal, and a second power supply which varies, in accordance with the second signal, a second current supplied to the spin torque oscillator.