Bilayer Field Generation Layer for Low Current Density MAMR
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Solution Overview
Problem
Microwave assisted magnetic recording (MAMR) devices face challenges in generating high-frequency magnetic fields at low current densities, leading to reliability concerns due to high critical current densities in the Field Generation Layer (FGL), which can be exacerbated by ferromagnetic resonance.
Innovation Solution
The solution involves replacing the conventional FGL with a bilayer structure where one sub-layer has perpendicular magnetic anisotropy (PMA) and the other has in-plane anisotropy, strongly exchange coupled to each other, ensuring the PMA sub-layer is closer to the spacer, facilitating low current density microwave generation by enhancing spin torque oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional FGL is used in MAMR devices, then the structure is simple, but the critical current density is high leading to reliability concerns
Solution Approach 1:
The FGL is divided into two sub-layers: a first sub-layer with perpendicular magnetic anisotropy (PMA) and a second sub-layer with in-plane anisotropy. This segmentation allows each sub-layer to contribute different magnetic properties, reducing the overall critical current density while maintaining the necessary magnetic field generation capability for MAMR operation.
Solution Approach 2:
The patent employs a composite FGL structure combining materials with different magnetic anisotropy characteristics. The first sub-layer uses materials exhibiting PMA (such as CoFeB or CoFe) while the second sub-layer uses materials with in-plane anisotropy (such as CoFe or Co), creating a composite structure that optimizes both magnetic field generation and current density reduction.
2Use of energy by moving object
If the FGL oscillation energy barrier is high, then the structure is stable, but microwave generation requires high current density
Solution Approach 1:
Different regions of the FGL are assigned different magnetic anisotropy properties to achieve local optimization. The first sub-layer near the spacer has PMA which facilitates low-current-density spin torque oscillation initiation, while the second sub-layer has in-plane anisotropy that provides stability. This local differentiation of magnetic properties allows microwave generation at low current densities while maintaining oscillation stability.
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 allows for efficient generation of microwaves at low current densities (as low as 1×10^8 A/cm2), improving the reliability and performance of MAMR devices by reducing the energy barrier for FGL oscillations and enhancing oscillation vigor.
Implementation Method 1
As electrons in oscillating stack 14 transit SIL 12 their spins become polarized by the magnetization present in SIL 12
Implementation Method 2
Spin torque oscillation then occurs in the FGL 13, resulting in the generation of microwaves
Implementation Method 3
Because of ferromagnetic resonance (FMR), it becomes possible to switch media grains at fields below their normal coercivity
Implementation Method 4
FGL1 and FGL2 are strongly exchange coupled to each other, they will be excited simultaneously to oscillate as though they were a single layer
Data Source
AI summary
A spin torque oscillator is described in which the conventional Field Generation Layer (FGL) is replaced by a bilayer, one of whose members exhibits perpendicular magnetic anisotropy while the other exhibits conventional in-plane anisotropy. Provided the layer with the perpendicular anisotropy is the one that is closest to the spacer layer, the device is able to generate microwaves at current densities as low as 1×108 A/cm2.