Spin-Torque Oscillator Seed Layer for Write Pole Spin Polarization
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Solution Overview
Problem
In perpendicular magnetic recording systems, the spin-polarization of electrons from the ferromagnetic write pole counteracts the spin transfer torque, hindering the effectiveness of the spin-torque oscillator (STO) in reducing the write field required for magnetization switching of magnetic grains.
Innovation Solution
A nonmagnetic electrically-conducting multilayer seed layer is introduced between the write pole and the ferromagnetic free layer to remove spin polarization from electrons, ensuring proper crystallographic texture and optimization of electron transport properties, while maintaining the STO's functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a ferromagnetic write pole is used in the spin-torque oscillator, then the write field is enhanced, but spin polarization of electrons counteracts the spin transfer torque
Solution Approach 1:
A nonmagnetic electrically-conducting seed layer is introduced as an intermediary between the ferromagnetic write pole and the ferromagnetic free layer. This seed layer serves as a mediator that allows electron transport while removing unwanted spin polarization through spin-flip scattering, thereby resolving the contradiction between maintaining write field enhancement and preserving spin transfer torque effectiveness.
Solution Approach 2:
The harmful spin polarization is extracted or removed from the electron flow by the nonmagnetic seed layer. The seed layer selectively removes the spin polarization component that would otherwise counteract the spin transfer torque, while allowing the electrons to continue transporting and enabling the desired magnetic switching function.
2Quantity of substance
If magnetic grain size is reduced to increase recording density, then recording density increases, but thermal stability of magnetic grains deteriorates
Solution Approach 1:
The invention changes the magnetic properties parameters by introducing the nonmagnetic seed layer, which modifies the magnetic anisotropy and coercivity of the free layer. This allows the system to achieve both reduced grain size for higher density and maintained thermal stability through optimized magnetic parameters enabled by the seed layer's spin polarization removal effect.
3Stability of the object's composition
If anisotropy of magnetic grains is increased to maintain thermal stability, then thermal stability is maintained, but the write field required increases
Solution Approach 1:
The invention substitutes the conventional purely magnetic write field mechanism with a spin-transfer torque mechanism assisted by the nonmagnetic seed layer. The spin-polarized electrons from the free layer, facilitated by the seed layer's polarization removal, provide a more efficient means to switch magnetization, reducing the mechanical write field force needed while maintaining high anisotropy for thermal 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
The multilayer seed layer enhances the spin transfer torque, allowing for reduced write fields and increased coercivity, thereby improving recording density and thermal stability of magnetic grains without adversely affecting the STO's performance.
Implementation Method 1
the spin-polarization of electrons from the ferromagnetic write pole counteracts the spin transfer torque
Implementation Method 2
the electrons are reflected from the trailing shield and become spin polarized by the polarizer, which creates the spin transfer torque on the magnetization of the free layer
Implementation Method 3
a high frequency oscillatory auxiliary magnetic field from a ferromagnetic free layer or field generation layer (FGL) in the STO is applied to the magnetic grains of the recording layer
Implementation Method 4
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 5
The STO electrical circuitry supplies DC current to the STO, with the electron flow being from the write pole to the trailing shield. The electrons are reflected from the trailing shield and become spin polarized by the polarizer, which creates the spin transfer torque on the magnetization of the free layer. This destabilizes the static equilibrium of the free layer's magnetization orientation, causing it to undergo sustained oscillation.
Data Source
AI summary
A magnetic recording write head and system has a spin-torque oscillator (STO) located between the write head's write pole and trailing shield. The STO's ferromagnetic free layer is located near the write pole with a multilayer seed layer between the write pole and the free layer. The STO's nonmagnetic spacer layer is between the free layer and the STO's ferromagnetic polarizer. The polarizer may be the trailing shield of the write head or a separate polarizer layer. The STO electrical circuitry causes electron flow from the write pole to the trailing shield. The multilayer seed layer removes the spin polarization of electrons from the write pole, which enables electrons reflected from the polarizer layer to become spin polarized, which creates the spin transfer torque on the magnetization of the free layer. The multilayer seed layer includes Mn or a Mn-alloy layer between one or more metal or metal alloy films.