AFM-FM Phase Change Spacer for PMR Write Pole Erasure
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Solution Overview
Problem
Perpendicular magnetic recording (PMR) technologies face challenges in minimizing data erasure due to remanent magnetic fields in write pole tips, which are exacerbated by the smaller size requirements for higher data density, leading to a trade-off between reducing pole erasure and maintaining a strong write field.
Innovation Solution
A laminated main pole layer using an antiferromagnetic-ferromagnetic (AFM-FM) phase change material as a spacer, which switches between AFM and FM states to minimize remanence during non-write operations and enhance write field during writing, utilizing FeRh or FeRhX alloys and localized heating to control the phase transition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the writer pole tip size is reduced to achieve higher data density, then the data density is improved, but the pole erasure increases due to remanent magnetic fields
Solution Approach 1:
The writer pole is divided into multiple thin ferromagnetic layers separated by non-magnetic spacer layers, creating a laminated structure. This segmentation allows the magnetic moments of adjacent layers to cancel each other through magneto-static coupling, reducing the net remanent magnetic field at the pole tip while maintaining the reduced pole tip size for high data density
Solution Approach 2:
Non-magnetic spacer layers (such as Ru or Cr) are introduced between adjacent ferromagnetic layers to mediate the magneto-static coupling interaction. These spacer layers enable the edge charge coupling that produces anti-parallel magnetization orientation in adjacent magnetic layers, leading to charge cancellation and reduced pole erasure
2Object-generated harmful factors
If a laminated multi-layer structure is used to reduce pole erasure, then the pole erasure is minimized, but the write field is reduced
Solution Approach 1:
The thickness parameters of both the ferromagnetic layers and non-magnetic spacer layers are optimized to achieve the desired balance. By controlling the layer thicknesses, the magneto-static coupling field is tuned to provide sufficient remanence reduction while maintaining adequate write field strength for effective magnetic recording
Solution Approach 2:
The laminated structure is applied specifically to the writer pole region where remanence reduction is most critical, while other parts of the magnetic head structure maintain their conventional design to preserve write field generation capabilities
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
The solution effectively reduces remanence and maintains a strong write field, enhancing writability and data integrity by leveraging the high magnetic moment of the FM state while minimizing pole erasure, as demonstrated by finite-element simulations showing improved write field and field gradient.
Implementation Method 1
A PMR head which combines the features of a single pole writer and a double layered media has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density.
Implementation Method 2
utilizing FeRh or FeRhX alloys and localized heating to control the phase transition
Implementation Method 3
heating/cooling can be realized by a separate heating coil in the write gap region near the write pole tip
Data Source
AI summary
A method of manufacturing a PMR writer is disclosed that minimizes pole erasure during non-writing and maximize write field during writing by including an AFM-FM phase change material spacer that is in an AFM state during non-writing and switches to a FM state by heating during writing. The main pole layer including the write pole may be formed as a laminated structure by a sputter deposition process wherein a plurality of “n” ferromagnetic layers and “n−1” AFM-FM phase change material layers are laid down in an alternating manner. The AFM-FM phase change material is preferably a FeRh or FeRhX alloy (X=Pt, Pd, or Ir) having a Rh content >35 atomic %, and may also be used as a flux gate to prevent yoke flux from leaking into the write pole tip.