Magnetoresistive Element Cap Layer Crystal Structure
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Solution Overview
Problem
Conventional magnetoresistive elements, particularly spin-valve films, face limitations in achieving high magnetoresistive ratios due to instability in crystal structure, leading to degraded interfacial sharpness, crystal orientation, and spin diffusion length, which reduces their magnetic recording and reproducing capabilities.
Innovation Solution
A magnetoresistive element comprising a magnetization pinned layer, a nonmagnetic spacer layer, and a magnetization free layer with specific crystal structures and a cap layer having an interatomic distance greater than the free layer, configured to supply a sense current perpendicular to the film planes, enhancing spin-dependent scattering and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a spin-valve structure with thin pinned layer and free layer (5 nm thickness) is used to achieve small device size, then the device dimensions are reduced, but the output absolute value becomes very small (about 0.5 mΩμm2) due to low resistance
Solution Approach 1:
The patent introduces a cap layer with specific crystal structure (hcp or bcc) and larger interatomic distance than the free layer to locally enhance spin scattering at the interface. This local modification of the cap layer's crystal structure creates stronger spin-dependent scattering without increasing the overall device dimensions, thereby maintaining small size while improving output signal strength through enhanced local scattering properties.
Solution Approach 2:
The patent employs a composite multilayer structure combining spin-valve layers (pinned layer, spacer layer, free layer) with a specifically engineered cap layer having different crystal structure characteristics. This composite structure integrates the functionality of thin layers for small size with the cap layer's enhanced scattering properties for improved output, achieving both miniaturization and high signal strength.
2Ease of manufacture
If conventional CIP type spin-valve structure is used, then the device is easy to manufacture, but the magnetoresistive ratio is limited to about 20% and output is low when current is supplied perpendicular to the film plane
Solution Approach 1:
The patent transitions from CIP (current-in-plane) to CPP (current-perpendicular-to-plane) geometry and modifies the cap layer's crystal structure parameters (hcp or bcc with larger interatomic distance) to dramatically enhance the magnetoresistive ratio. This parameter change in current direction and cap layer structure enables the magnetoresistive ratio to exceed 20%, achieving high output while maintaining manufacturability through standard sputtering processes.
3Stability of the object's composition
If the cap layer has smaller or equal interatomic distance compared to the free layer, then the crystal structure remains stable, but the spin diffusion length is reduced and magnetoresistive ratio is limited
Solution Approach 1:
The patent creates a local quality difference by designing the cap layer with larger interatomic distance than the free layer, which paradoxically enhances spin diffusion length. This local structural modification at the cap layer interface creates favorable conditions for spin transport while maintaining overall crystal structure stability through controlled epitaxial growth relationships between layers.
Solution Approach 2:
The patent changes the interatomic distance parameter of the cap layer to be larger than that of the free layer, which fundamentally alters the spin scattering characteristics. This parameter change in interatomic distance enhances the spin diffusion length and magnetoresistive ratio while the cap layer's crystal structure (hcp or bcc) maintains sufficient stability for device operation.
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 proposed configuration improves the magnetoresistive ratio by stabilizing the crystal structure, enhancing interfacial sharpness, and increasing spin diffusion length, resulting in higher magnetic recording and reproducing performance.
Implementation Method 1
The magnetoresistive ratio (MR ratio) of the spin-valve is expressed by the formula: MR=ΔRsd/(Rsi+Rsd). The insertion of the resistance increasing layer including the insulator into the spin-valve film is intended to obtain improved MR ratio by making Rsd far higher than Rsi.
Implementation Method 2
a multilayered film with a sandwich structure including a ferromagnetic layer, a nonmagnetic layer and a ferromagnetic layer successfully produces a high magnetoresistive effect
Implementation Method 3
A magnetoresistive element comprising a magnetization pinned layer, a nonmagnetic spacer layer, and a magnetization free layer with specific crystal structures and a cap layer having an interatomic distance greater than the free layer, configured to supply a sense current perpendicular to the film planes, enhancing spin-dependent scattering and stability.
Implementation Method 4
the total thickness of the spin-dependent layers is very small and the number of interfaces is also small. Accordingly, if a spin-valve with a structure employed in the conventional CIP type is supplied with a current in the direction perpendicular to the film plane, the element shows a low resistance
Data Source
AI summary
A magnetoresistive element has a magnetization pinned layer, a nonmagnetic spacer layer including a stack of a nonmagnetic metal layer, a resistance increasing layer and another nonmagnetic metal layer, a magnetization free layer having an fcc crystal structure, a cap layer having an fcc, an hcp, or a bcc crystal structure and having an interatomic distance between nearest neighbors greater than that of the magnetization free layer, and a pair of electrodes configured to provide a sense current in a direction substantially perpendicular to planes of the magnetization pinned layer, the nonmagnetic spacer layer, and the magnetization free layer.