MAMR Write Head Insulating Layer Design
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Solution Overview
Problem
Magnetic recording systems face a conflict between reducing magnetic grain size for higher recording density and maintaining thermal stability, as the magnetic write field must exceed the coercivity of the recording layer, leading to increased magnetic reluctance in MAMR write heads, which requires higher write current and frequency.
Innovation Solution
The MAMR write head design includes a yoke structure with an electrically insulating layer between the write pole and sub pole, allowing for an electrically conductive path for the STO current while minimizing magnetic reluctance, thereby reducing the required write current and increasing the magnetic flux area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the insulating gap is located in the back region behind the coil and between a portion of the yoke and the write pole, then the STO current circuit is completed, but the magnetic flux path becomes narrow and magnetic reluctance increases
Solution Approach 1:
The patent moves the insulating gap from the back region (behind the coil) to the front region (at the disk-facing surface) of the write head. This spatial repositioning in a different dimension allows the magnetic flux path to remain open and wide, reducing magnetic reluctance while still completing the STO current circuit through the yoke structure.
Solution Approach 2:
The patent introduces a nonmagnetic spacer layer as an intermediary element between the write pole and the trailing shield. This spacer layer provides the necessary insulation for the STO current circuit while maintaining an open magnetic flux path, effectively mediating between the electrical insulation requirement and the magnetic flux requirement.
2Productivity
If magnetic grain size is reduced to increase recording density, then recording density increases, but thermal stability decreases
Solution Approach 1:
The patent employs periodic microwave oscillations from the STO at frequencies near the resonance frequency of the magnetic grains. This periodic action temporarily reduces the effective coercivity during the oscillation cycles, allowing smaller magnetic grains to be switched more easily while maintaining thermal stability between cycles.
Solution Approach 2:
The patent utilizes the phase transition-like behavior of magnetization switching under microwave assistance. The microwave field induces transitions between magnetized states in the magnetic grains, enabling reliable switching of smaller grains that would otherwise be too stable to switch with conventional write fields.
3Reliability
If magnetic write field is increased to exceed coercivity for saturation digital recording, then recording reliability improves, but the conflict with anisotropy limitation increases
Solution Approach 1:
The patent uses periodic microwave oscillations to periodically reduce the effective energy barrier for magnetization switching. This allows the write head to achieve saturation digital recording with lower peak write fields by timing the write field application with the microwave oscillation cycles when the magnetization is most susceptible to switching.
Solution Approach 2:
The patent changes the effective coercivity parameter of the magnetic recording layer through microwave assistance. The STO-generated microwave field dynamically modifies the magnetic anisotropy energy landscape, effectively lowering the coercivity during switching events and enabling saturation recording without requiring excessively high write fields that would conflict with anisotropy limitations.
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 design achieves a significant increase in write field with less write current, reducing the risk of adjacent track interference and enabling higher recording density without increasing write current levels.
Implementation Method 1
the spin-torque oscillator (STO) is located between the write pole and the trailing magnetic shield. The STO is a multilayer film stack made up of two or more magnetic layers separated by a nonmagnetic spacer layer. One of the magnetic layers, the field generating layer (FGL), is designed to have its magnetization orientation oscillate in the presence of a direct electrical current perpendicular to the film planes of the film stack.
Implementation Method 2
The auxiliary field may have a frequency close to the resonance frequency of the magnetic grains in the recording layer to facilitate the switching of the magnetization of the grains
Implementation Method 3
The insulating layer between the write pole and the sub pole assures that the STO current is not shorted between the return pole and the write pole
Implementation Method 4
the yoke structure provides an electrical circuit for supply current to the STO
Implementation Method 5
this location provides a relatively narrow flux path and thus increases the magnetic reluctance of the magnetic circuit
Data Source
AI summary
A microwave-assisted magnetic recording (MAMR) write head includes a yoke structure with a main pole, a flux return pole, and a trailing magnetic shield. The main pole includes a write pole with a tip at the disk-facing surface, a sub pole with an end recessed from the disk-facing surface and an electrically insulating layer between the write pole and the sub pole. The spin-torque oscillator (STO) is located at the disk-facing surface between the trailing shield and the write pole tip. The insulating layer assures that the STO current is not shorted between the return pole and the write pole. The insulating layer between the write pole and the sub pole increases the area of the junction between the return pole and write pole, which reduces the magnetic reluctance of the yoke structure.