Magnetoresistive Element with Antiferromagnetic Bias Layer
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Solution Overview
Problem
Magnetoresistive elements used in magnetic recording media are susceptible to external magnetic fields and thermal noise, especially as they are miniaturized to achieve higher recording densities, leading to reduced operational reliability.
Innovation Solution
A magnetoresistive element with a stacked structure including a magnetically pinned layer, a non-magnetic layer, a magnetically free layer, and an antiferromagnetic bias layer, where the exchange-coupling magnetic field between the free layer and the bias layer is smaller than the saturation magnetic field, allowing for gentle magnetization variation in lower magnetic fields and sensitive response in higher fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the size of magnetoresistive elements is reduced to achieve higher recording density, then the recording density is improved, but the element becomes more susceptible to external magnetic fields and thermal noise, reducing operational reliability
Solution Approach 1:
The patent employs a composite layered structure consisting of a magnetically pinned layer, a nonmagnetic layer, a magnetically free layer, and an antiferromagnetic bias layer. This composite structure enables the element to maintain high recording density while improving reliability through exchange coupling between the free layer and bias layer, which provides magnetic field immunity and noise resistance.
Solution Approach 2:
The patent optimizes the exchange-coupling magnetic field parameter by adjusting the thickness and material composition of the antiferromagnetic bias layer and its interface with the free layer. By controlling this parameter to be smaller than the saturation magnetic field, the element achieves gentle magnetization variation in low fields (reducing noise susceptibility) while maintaining sensitive response in high signal fields.
2Reliability
If the exchange-coupling magnetic field is made smaller than the saturation magnetic field, then the susceptibility to unnecessary magnetic fields and noise is reduced, but the sensitivity to detect weak signal magnetic fields may be compromised
Solution Approach 1:
The patent creates different magnetic field response characteristics in different operating regions. In low magnetic field regions (noise and interference), the exchange coupling produces gentle magnetization variation for stability. In high magnetic field regions (signal detection), the magnetization responds sensitively, enabling precise detection. This local quality differentiation resolves the contradiction between noise immunity and detection sensitivity.
3Stability of the object's composition
If a pair of magnetic domain controlling layers are used to give uniform bias magnetic field, then the magnetization uniformity is improved, but the device complexity increases
Solution Approach 1:
The patent extracts and consolidates the bias magnetic field generation function into a single antiferromagnetic bias layer that is exchange-coupled with the free layer. This eliminates the need for a pair of magnetic domain controlling layers while maintaining uniform magnetization, thereby reducing device complexity without sacrificing magnetization uniformity.
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 enhances the reliability of magnetoresistive elements by reducing their susceptibility to unnecessary magnetic fields and noise, enabling precise detection of signal magnetic fields while maintaining high recording density capabilities.
Implementation Method 1
an antiferromagnetic bias layer exchange-coupled with the magnetically free layer are stacked in order, and an exchange-coupling magnetic field between the magnetically free layer and the antiferromagnetic bias layer
Implementation Method 2
a magnetoresistive element exhibiting giant magnetoresistive effect
Implementation Method 3
a magnetic layer whose magnetization direction is varied in accordance with an external signal magnetic field applied from outside (magnetically free layer)
Data Source
AI summary
The invention is devised to provide a magnetoresistive element that is hardly susceptible to harmful influence of unnecessary magnetic fields and noise of heat even when reduction in size is achieved to be adaptable to higher recording density, and therefore that is excellent in operational reliability. The magnetoresistive element includes a stacked structure including, in order: a magnetically pinned layer whose magnetization direction is fixed in a given direction; a non-magnetic layer; a magnetically free layer whose magnetization direction changes according to an external magnetic field; and an antiferromagnetic bias layer exchange-coupled with the magnetically free layer. The exchange-coupling magnetic field between the magnetically free layer and the antiferromagnetic bias layer is smaller than a saturation magnetic field of the magnetically free layer.