Heusler Alloy Insertion Layer Reduces Ordering Temperature
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Solution Overview
Problem
Heusler alloys like Co2MnSi require high temperature annealing to achieve ordered half metal structures, which damages underlying substrates and degrades pinning strength in magnetic sensors, limiting their application in high-density recording devices.
Innovation Solution
A laminated structure with Al or FeCo insertion layers in Heusler alloys as AP1 and/or free layers in CPP-GMR sensors, reducing the ordering temperature to a compatible range for spintronics devices and preserving spin polarization, allowing for improved MR ratios and resistance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature annealing is applied to achieve ordered half metal structure in Heusler alloys, then spin polarization and MR ratio are improved, but underlying substrates are damaged and pinning strength is degraded
Solution Approach 1:
A non-magnetic spacer layer (Ru, Rh, Ir, Cu, Ag, Au, or their alloys) is introduced as an intermediary between the Heusler alloy layer and the underlying substrate/pinned layer. This spacer layer acts as a thermal buffer that protects the substrate and pinned layer from high temperature annealing damage while allowing the Heusler alloy to achieve its ordered half-metal structure. The spacer has high thermal stability and does not diffuse into the Heusler alloy during annealing, thus preserving the pinning strength of the underlying layers.
2Reliability
If high temperature annealing is applied to achieve ordered half metal structure in Heusler alloys, then spin polarization and MR ratio are improved, but pinning strength is degraded
Solution Approach 1:
The non-magnetic spacer layer serves as a protective intermediary that physically separates the Heusler alloy from the pinned layer, preventing thermal degradation of the pinning interface during high temperature annealing. This allows the Heusler alloy to be annealed at temperatures above 300°C to achieve optimal spin polarization without compromising the pinning strength of the underlying AFM/pinned layer structure.
3Reliability
If Heusler alloy is used as AP1 or free layer in CPP-GMR sensor, then MR ratio is enhanced, but high temperature processing is required which limits device integration
Solution Approach 1:
The non-magnetic spacer layer enables high temperature annealing of the Heusler alloy to achieve ordered half-metal structure and high MR ratio, while simultaneously protecting the underlying device structure from thermal damage. This makes the Heusler-based CPP-GMR sensor compatible with standard semiconductor fabrication processes that cannot accommodate temperatures above 300°C, thus improving ease of manufacture and device integration.
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 use of Al or FeCo insertion layers in Heusler alloys reduces the ordering temperature, enabling practical integration in magnetic sensors with enhanced MR ratios and resistance values, suitable for high-density recording applications.
Implementation Method 1
Heusler alloy with insertion layer to reduce the ordering temperature for CPP, TMR, MRAM, and other spintronics applications
Implementation Method 2
preserving spin polarization, allowing for improved MR ratios and resistance values
Implementation Method 3
The rotation of magnetization in the free layer relative to the fixed layer magnetization generates a resistance change that is detected as a voltage change when a sense current is passed through the structure
Data Source
AI summary
A spin valve structure is disclosed in which an AP1 layer and/or free layer are made of a laminated Heusler alloy having Al or FeCo insertion layers. The ordering temperature of a Heusler alloy such as Co2MnSi is thereby lowered from about 350° C. to 280° C. which becomes practical for spintronics device applications. The insertion layer is 0.5 to 5 Angstroms thick and may also be Sn, Ge, Ga, Sb, or Cr. The AP1 layer or free layer can contain one or two additional FeCo layers to give a configuration represented by FeCo/[HA/IL]nHA, [HA/IL]nHA/FeCo, or FeCo/[HA/IL]nHA/FeCo where n is an integer ≧1, HA is a Heusler alloy layer, and IL is an insertion layer. Optionally, a Heusler alloy insertion scheme is possible by doping Al or FeCo in the HA layer. For example, Co2MnSi may be co-sputtered with an Al or FeCo target or with a Co2MnAl or Co2FeSi target.