Flux Guiding Devices in Perpendicular Magnetic Recording Writers
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Solution Overview
Problem
Current perpendicular magnetic recording (PMR) writers face challenges in enhancing write performance without compromising cross-track and down-track performance, particularly in maintaining write field strength and gradient while dealing with the limitations of spin torque oscillator (STO) devices in microwave assisted magnetic recording (MAMR) systems.
Innovation Solution
Incorporating a flux guiding (FG) device with a spin polarization layer, non-magnetic layers, and a flux guiding layer in the write gap, leading gap, and side gaps, and replacing conventional magnetic shields with non-magnetic conducting layers to flip the magnetization direction of the flux guiding layer when a current is applied, thereby increasing the reluctance and enhancing the write field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If flux guiding devices are inserted in the write gap, side gaps, and leading gap around the main pole to increase reluctance and force additional flux out of the main pole tip, then the write field on the magnetic recording medium is enhanced, but the device complexity increases due to the additional layers and structures required
Solution Approach 1:
The flux guiding devices are nested within the existing writer structure by inserting FG layers into the write gap, side gaps, and leading gap regions. These FG layers are positioned between existing components (main pole, shields, and non-magnetic layers) without requiring complete disassembly or major structural redesign, thus enhancing write field while managing complexity through strategic nesting
Solution Approach 2:
The flux guiding functionality is segmented into multiple discrete FG layers positioned at different locations (write gap FG layer, side gap FG layers, leading gap FG layer) rather than using a single complex structure. This segmentation allows independent optimization of each FG layer's properties and simplifies the overall design by breaking down the complex flux control function into manageable segments
2Power
If the magnetization of the flux guiding layer is flipped to the opposite direction by applying current across the gaps, then the reluctance in the gaps increases and more magnetic flux is concentrated orthogonal to the air bearing surface, but the use of energy increases due to the current required for magnetization switching
Solution Approach 1:
The magnetization switching of the flux guiding layer is performed periodically in sync with the writing operation rather than continuously. Current is applied across the gaps only when needed to flip the magnetization direction for enhancing the write field, and then discontinued, thus reducing overall energy consumption while maintaining effective write field enhancement during critical writing moments
Solution Approach 2:
The magnetization state of the flux guiding layer is dynamically changed between two stable states (original direction and flipped opposite direction) based on writing requirements. By switching between these discrete parameter states rather than maintaining continuous high-energy states, the system achieves effective flux control with reduced energy consumption
3Reliability
If non-magnetic conducting layers are used to replace leading shield and side shields, then resistance to wear and corrosion is improved, but the ability to control magnetic flux leakage is reduced
Solution Approach 1:
Flux guiding layers are introduced as intermediary magnetic structures between the main pole and the non-magnetic conducting shield layers. These FG layers act as mediators that actively control and direct the magnetic flux, compensating for the reduced flux control capability of the non-magnetic shields while allowing the non-magnetic layers to provide their wear and corrosion protection benefits
Solution Approach 2:
The writer structure employs a composite configuration combining non-magnetic conducting layers (for wear and corrosion resistance) with magnetic flux guiding layers (for flux control). This composite approach integrates the advantages of both material types: the non-magnetic layers provide enhanced reliability against wear and corrosion, while the magnetic FG layers compensate for the loss of flux control, achieving both protection and functional performance
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 improves down-track performance with a stronger write field and field gradient without degrading cross-track performance, reducing bit error rate and allowing for adjustable erase width in alternating current mode, while providing improved resistance to wear and corrosion.
Implementation Method 1
STO devices are based on a spin-torque-transfer effect that arises from the spin dependent electron transport properties of ferromagnetic (FM1)-spacer-ferromagnetic (FM2) multilayers. When spin polarized current from the FM1 layer passes through the spacer and FM2 layer in a current perpendicular-to-plane direction, the spin angular moment of electrons incident on the FM2 layer interacts with magnetic moments of the FM2 layer near the interface between the FM2 layer and the non-magnetic spacer. Through this interaction, the electrons transfer a portion of their angular momentum to the FM2 layer. As a result, spin-polarized current can switch (flip) the FM2 magnetization direction if the current density is sufficiently high.
Implementation Method 2
there is increased reluctance in the write gap so that more magnetic flux from the MP will be concentrated in a direction orthogonal to the ABS to assist writing
Data Source
AI summary
A perpendicular magnetic recording writer has a main pole (MP) with a first flux guiding (FG) device in a write gap between the MP trailing side and a trailing shield, a second FG device in each side gap and adjoining a MP side, and third FG device in the leading gap and adjoining the MP leading side. At least one of a first and second non-magnetic conductive layer (NMC1 and NMC2) contacts the third FG device and second FG devices, respectively, instead of a conventional leading shield and side shield. Each FG device has a flux guiding layer (FGL) with a magnetization that flips to oppose a gap flux field when a current is applied across the respective gap thereby enhancing the MP write field. NMC1 and NMC2 allow better wear and corrosion resistance in addition to improved return field and down-track field gradient, and acceptable side shield stray field.