NiFe Alloy Pinned Layer for High Delta R A Magnetic Sensors
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Solution Overview
Problem
Current CPP-type magnetic sensors face challenges in achieving a high product of change in resistance (ΔR) and element area (A), specifically ΔR·A of 5 mΩ·μm2 or more, due to limitations in the composition of the NiFe alloy used in the pinned magnetic layer, which affects the sensor's reproduction output and magnetostrictive constant.
Innovation Solution
The magnetic sensor incorporates a pinned magnetic layer with a NiFe alloy having a Ni content between 0 to 25 atomic percent, forming a NiaFeb alloy layer, which increases the ΔR·A product and magnetostrictive constant, and optionally includes a three-layered structure with CoFe layers to prevent diffusion and enhance uniaxial anisotropy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional NiFe alloy (80 atomic percent Ni) is used for the pinned magnetic layer, then the alloy has high spin polarization, but the product of change in resistance and element area (ΔR·A) remains below 5 mΩ·μm2
Solution Approach 1:
The patent applies parameter changes by modifying the Ni content in the NiFe alloy from the conventional 80 atomic percent to a range of 40-70 atomic percent. This compositional parameter change increases the magnetostrictive constant and uniaxial anisotropy, thereby achieving a ΔR·A product of 5 mΩ·μm2 or more while maintaining the alloy's functionality in the pinned magnetic layer.
Solution Approach 2:
The patent employs composite materials by creating a multi-layered pinned magnetic layer structure that includes NiFe alloy layers with specific compositions (40-70 atomic percent Ni) combined with other functional layers. This composite structure leverages the high spin polarization of NiFe while incorporating layers that provide enhanced magnetostrictive properties and uniaxial anisotropy to achieve the target ΔR·A product.
2Power
If the Ni content in the NiFe alloy is increased to 80 atomic percent, then the spin polarization is high, but the magnetostrictive constant and uniaxial anisotropy are insufficient
Solution Approach 1:
The patent changes the compositional parameter of Ni content from 80 atomic percent to 40-70 atomic percent, which fundamentally alters the material properties. This parameter change simultaneously increases the magnetostrictive constant and uniaxial anisotropy while maintaining sufficient spin polarization through the optimized composition range and multi-layer structure.
Solution Approach 2:
The patent uses composite materials by constructing a pinned magnetic layer with multiple layers including NiFe alloy layers (40-70 atomic percent Ni) and other magnetic layers. This composite structure compensates for the reduced Ni content by incorporating layers with complementary properties, thereby achieving high magnetostrictive constant and reliable magnetization pinning simultaneously.
3Measurement precision
If a simple NiFe alloy layer is used for the pinned magnetic layer, then the structure is simple, but the uniaxial anisotropy and reproduction output are insufficient
Solution Approach 1:
The patent applies composite materials by designing a pinned magnetic layer with a multi-layer structure that includes NiFe alloy layers with specific compositions (40-70 atomic percent Ni) combined with other functional magnetic layers. This composite structure enhances uniaxial anisotropy and reproduction output through the synergistic effects of different layers while maintaining manufacturing feasibility.
Solution Approach 2:
The patent applies segmentation by dividing the pinned magnetic layer into multiple distinct layers with different compositions and functions. Each layer is optimized for specific purposes (e.g., spin polarization, magnetostriction, anisotropy), and their combined effect achieves high reproduction output. The segmentation allows independent optimization of each layer's properties.
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 configuration significantly increases the ΔR·A product to 5 mΩ·μm2 or more, enhancing the sensor's reproduction output and uniaxial anisotropy, thereby improving the detection of magnetic fields.
Implementation Method 1
the magnetostrictive constant of the pinned magnetic layer can be increased, and hence the uniaxial anisotropy thereof can be increased
Implementation Method 2
An exchange coupling magnetic field is generated at the interface between the antiferromagnetic layer 3 and the pinned magnetic layer 4, and the magnetization of the pinned magnetic layer 4 is pinned in a height direction
Implementation Method 3
By a longitudinal bias magnetic field applied from the hard bias layers 8, the magnetization of the free magnetic layer 6 is aligned in a track width direction
Implementation Method 4
When an exterior magnetic field is applied to the magnetic sensor, the magnetization direction of the free magnetic layer is relatively changed with respect to that of the pinned magnetic layer, and as a result, the resistance of the multilayer film is changed
Data Source
AI summary
A magnetic sensor comprising: a multilayer film which has a pinned magnetic layer, the magnetization thereof being pinned in one direction, and a free magnetic layer formed on the pinned magnetic layer with a nonmagnetic material layer provided therebetween, in which current is allowed to flow in a direction perpendicular to the surfaces of the layers forming the multilayer film, wherein the pinned magnetic layer has a NiaFeb alloy layer (where a and b each indicate atomic percent, and 0<a≦25 and a+b=100 are satisfied).