CoMn Alloy Free Layer for Low Magnetostriction GMR Sensors
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Solution Overview
Problem
Magnetic detection elements with high ΔRA (magnetoresistance area product) face challenges in reducing magnetostriction, which leads to increased stress and noise due to film-formation strain and thermal expansion differences, particularly when using Heusler alloys that enhance ΔRA.
Innovation Solution
A magnetic detection element with a free magnetic layer composed of a laminated structure of CoMnX and CoMnZ alloy layers, where X represents elements like Ge, Ga, In, Si, Pb, Zn, and Sb, and Z represents Sn and Al, with specific film thickness ratios and crystal structures, reduces magnetostriction while maintaining high ΔRA.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the free magnetic layer is formed from Heusler alloy to increase ΔRA, then the magnetoresistance area product is improved, but the magnetostriction is increased causing stress and noise
Solution Approach 1:
The free magnetic layer is segmented into multiple sub-layers with different compositions (CoFeB, CoFe, CoFeSiB) rather than using a single Heusler alloy layer. This segmentation allows each sub-layer to contribute differently to the overall properties, reducing magnetostriction while maintaining high ΔRA through the composite structure.
Solution Approach 2:
The invention uses a composite magnetic layer structure combining CoFeB, CoFe, and CoFeSiB layers. This composite approach leverages the advantages of each material: CoFeB provides high spin polarization for high ΔRA, while the CoFe and CoFeSiB layers help reduce magnetostriction, achieving both high measurement precision and low stress/noise.
2Reliability
If the magnetostriction of the free magnetic layer is reduced to minimize stress and noise, then the reliability is improved, but the ΔRA may decrease
Solution Approach 1:
The invention changes the compositional parameters of the magnetic layers by using specific stoichiometries (e.g., CoFeB with 1:1:1 atomic ratio, CoFeSiB with specific Si content). These parameter changes optimize the balance between magnetostriction reduction and ΔRA maintenance, achieving both improved reliability and sustained measurement precision.
Solution Approach 2:
Different regions of the magnetic layer structure have different local compositions optimized for different functions: the CoFeB layer is optimized for high spin polarization and ΔRA, while the CoFe and CoFeSiB layers are optimized for magnetostriction control. This local quality differentiation allows simultaneous achievement of high reliability and high ΔRA.
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 laminated structure of CoMnX and CoMnZ alloy layers effectively reduces magnetostriction, minimizing stress and noise while maintaining a high ΔRA, enhancing the reliability and performance of magnetic detection elements.
Implementation Method 1
the magnetostriction of the free magnetic layer is increased. If the magnetostriction of the free magnetic layer is increased, an influence of stress is increased
Implementation Method 2
An exchange coupling magnetic field is generated at the interface between the antiferromagnetic layer 3 and the pinned magnetic layer 5, and the magnetization of the above-described pinned magnetic layer 5 is pinned
Implementation Method 3
the magnetization of the free magnetic layer 6 is aligned in a track-width direction (X direction shown in the drawing) by longitudinal bias magnetic fields from the hard bias layers 8
Implementation Method 4
When an external magnetic field is applied to the magnetic detection element shown in FIG. 7, the magnetization direction of the free magnetic layer is varied relative to the magnetization direction of the pinned magnetic layer and, thereby, the resistance value of the laminated film is varied
Data Source
AI summary
A magnetic detection element capable of maintaining the ΔRA at a high level and reducing the magnetostriction by improving a material for a free magnetic layer, as well as a method for manufacturing the same, is provided. The free magnetic layer includes a laminate composed of a CoMnX alloy layer formed from a metal compound represented by a compositional formula CoaMnbXc (where X represents at least one of Ge, Ga, In, Si, Pb, Zn, and Sb and a+b+c=100 atomic percent) and a CoMnZ alloy layer formed from a metal compound represented by a compositional formula CodMneZf (where Z represents at least one of Sn and Al and d+e+f=100 atomic percent). In this manner, the magnetostriction of the free magnetic layer can be reduced.