Magnetic Detectible Head Free Layer NiFe Alloy Composition
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Solution Overview
Problem
Conventional CPP magnetic detecting elements face challenges in controlling the product ΔRA of resistance variation and area, making it difficult to achieve a practical producing output of 5 mΩμm2 or more, even when using NiFe alloys as the free magnetic layer.
Innovation Solution
A magnetic detecting element with a free magnetic layer composed of an NiFe alloy where the at % of Ni is greater than 0 and not more than 25, and a three-layer structure with CoFe layers on either side of the NiFe alloy layer, along with a fixed magnetic layer that includes a CO2YZ alloy, enhances the product ΔRA of resistance variation and area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional NiFe alloys with Ni content of 40-80 at % are used in the free magnetic layer, then the soft magnetic properties are excellent, but the product ΔRA of resistance variation and area cannot be controlled to achieve 5 mΩμm2 or more
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Ni content in the NiFe alloy to be 40 at % or less (specifically 30-40 at %), which is a deviation from conventional compositions. This compositional parameter change enables simultaneous achievement of good soft magnetic properties and sufficient ΔRA product (5 mΩμm2 or more), resolving the contradiction between magnetic property quality and output control precision.
Solution Approach 2:
The patent uses composite material structure by combining NiFe alloy with specific perpendicular magnetic anisotropy (PMA) characteristics with the spin valve structure. The free magnetic layer is designed as a composite system where NiFe alloy provides soft magnetic properties while the layered structure with specific thickness ratios (t1/t2 between 0.3-0.7) provides the necessary magnetoresistance effect, achieving both soft magnetic performance and sufficient ΔRA product.
2Measurement precision
If the free magnetic layer is made thinner to increase sensitivity, then the magnetoresistance effect is enhanced, but the product ΔRA and reproducing output decrease
Solution Approach 1:
The patent applies parameter changes by optimizing the thickness parameters t1 and t2 of the magnetic layers such that their ratio t1/t2 falls between 0.3 and 0.7. This parameter optimization allows the free magnetic layer to maintain sufficient thickness for adequate reproducing output while still providing enough magnetoresistance effect for high sensitivity, thus resolving the contradiction between sensitivity and output power.
Solution Approach 2:
The patent introduces dynamic balance by establishing an optimal thickness ratio range (t1/t2 = 0.3-0.7) rather than fixing absolute thickness values. This dynamic approach allows the system to maintain the optimal balance between sensitivity and output across different device configurations and manufacturing variations, enabling simultaneous achievement of high measurement precision and sufficient power.
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 increases the product ΔRA of resistance variation and area to 5 mΩμm2 or more, improving the magnetic detecting element's sensitivity and output.
Implementation Method 1
An exchange-coupling magnetic field is generated at the interface between the antiferromagnetic layer 6 and the fixed magnetic layer 5, and magnetization of the fixed magnetic layer 5 is fixed in a height direction (Y-direction)
Implementation Method 2
Magnetized directions of the free magnetic layer 3 are arranged in a track width direction (X-direction in the drawing) by a longitudinal bias electric field from the hard bias layers 8
Implementation Method 3
If an external magnetic field is applied to the magnetic detecting element shown in FIG. 5, the magnetized direction of the free magnetic layer changes relatively with respect to the magnetized direction of the fixed magnetic layer, and the resistance value of the multilayer film changes
Data Source
AI summary
There is provided a magnetic detecting element having a large ΔRA. A free magnetic layer has a three layer structure in which a CoFe layer, an NiaFeb alloy layer (where a and b are represented by at %, 0≦a≦25, and a+b=100), and a CoFe layer are laminated from the bottom. If the at % of Ni in an NiFe alloy that exists in the free magnetic layer is in this range, a spin-dependent bulk scattering coefficient β increases, and the product ΔRA of the resistance variation of the magnetic detecting element and the area of the element can be made increased.