Spin Torque Oscillator with Low-Moment SPL for Stable MAMR Oscillation

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Solution Overview

Problem

Existing MAMR recording heads with spin torque oscillators (STOs) face inefficiencies and unstable oscillation states due to anti-parallel magnetization directions in the spin polarization layer (SPL) and field generation layer (FGL), leading to weak AC magnetic fields and unstable behavior.

Innovation Solution

The MAMR head incorporates an STO with a high perpendicular magnetic anisotropy spin polarization layer, an interlayer, a field generation layer, and a capping layer, where the current flows from the FGL to the SPL, resulting in an anti-parallel magnetization direction to the head-gap field, utilizing both direct and reflect torques for efficient oscillation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If anti-parallel magnetization directions are used in SPL and FGL, then both direct torque and reflect torque are utilized for efficient oscillation, but the magnetizations partially cancel each other leading to weak AC magnetic field and unstable oscillation behavior

Engineering Contradiction:

Improvespin torque efficiencyVSAvoidoscillation stability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent changes the magnetic moment parameter of the SPL by selecting specific materials (CoFeB, CoFe, CoNiB) and controlling thickness (3-10 nm), making the SPL magnetic moment smaller than the FGL magnetic moment. This parameter change prevents magnetization cancellation while maintaining both direct and reflect torque mechanisms, resolving the contradiction between spin torque efficiency and oscillation stability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material structures for both SPL and FGL, using combinations such as CoFeB/MgO, CoFe/MgO, or CoNiB/MgO. These composite materials enable precise control of magnetic moments and perpendicular magnetic anisotropy, allowing the system to achieve both high spin torque efficiency and stable oscillation by preventing magnetization cancellation

Inventive Principle:

Principle #40Composite materials

2Reliability

If T-mode oscillation with perpendicular magnetization directions is used, then head-gap field is parallel to SPL magnetization, but reflect torque has low efficiency

Engineering Contradiction:

Improveoscillation stabilityVSAvoidspin torque efficiency

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent inverts the conventional T-mode configuration by making the SPL magnetization anti-parallel to the head-gap field rather than parallel. This inversion, combined with the smaller SPL magnetic moment, allows both direct and reflect torque to contribute constructively, significantly improving spin torque efficiency while maintaining oscillation stability through the anti-parallel configuration

Inventive Principle:

Principle #13The other way round (Inversion)

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 configuration achieves high spin torque efficiency, a stable oscillation state, and a lower magnetic moment for the SPL, enhancing recording quality and reliability with reduced drive-voltage requirements.

Implementation Method 1

The STO generates high frequency magnetic fields, or microwaves, as a result of the transfer of spin torque from the SPL through the interlayer to the FGL

Methodology Applied

Scientific EffectSpin torque:

Implementation Method 2

The SPL is comprised of a high perpendicular magnetic anisotropy material. The SPL has a large effective perpendicular magnetic anisotropy field

Methodology Applied

Scientific EffectPerpendicular magnetic anisotropy: Anisotropy

Implementation Method 3

An applied current is adapted to flow in a direction from the FGL to the SPL resulting in the magnetization direction of the SPL being anti-parallel to a head-gap magnetic field due to a relation between a first spin torque directed from the SPL to the FGL and a second spin torque directed from the FGL to SPL

Methodology Applied

Scientific EffectSpin transfer torque:

Data Source

PatentUS20160148627A1Spin torque oscillator with low magnetic moment and high perpendicular magnetic anisotropy material

Publication Date: 2016.05.26 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

Embodiments disclosed herein generally relate to a magnetic disk device employing a MAMR head. The MAMR head includes an STO. The STO comprises an underlayer, an SPL, an interlayer, an FGL, and a capping layer. The SPL is comprised of a high perpendicular magnetic anisotropy material. The SPL has a large effective perpendicular magnetic anisotropy field, and the SPL has a lower magnetic moment than the FGL. An applied current is adapted to flow in a direction from the FGL to the SPL resulting in the magnetization direction of the SPL being almost perpendicular to the FGL and anti-parallel to a head-gap magnetic field due to a relation between a first spin torque directed from the SPL to the FGL and a second spin torque directed from the FGL to the SPL.