Permanent Magnet Growth Layer Coercive Field H* Optimization

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Solution Overview

Problem

Existing permanent magnets used in magnetic field sensors face a contradiction between generating a significant magnetic field and maintaining a coercive field H* that is far away from the ordinate axis, which is essential for insensitivity to exterior magnetic perturbations and improved dynamics, but increasing the number of patterns in the stack deteriorates H*.

Innovation Solution

Introducing a growth layer with nonmagnetic material between antiferromagnetic layers of successive patterns improves the coercive field H* and squareness, while maintaining a limited total volume of growth layers to avoid increased complexity, and using materials like tantalum and RKKY coupling to enhance the magnetic properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If the number of patterns in the stack is increased to generate a significant magnetic field, then the magnetic field strength is improved, but the coercive field H* deteriorates and moves closer to the ordinate axis

Engineering Contradiction:

Improvemagnetic field strengthVSAvoidcoercive field H* position

Core Design Contradiction:

ForceVSReliability

Solution Approach 1:

A growth layer of nonmagnetic material is introduced as an intermediary between the antiferromagnetic layers of successive patterns. This growth layer mediates the interaction between patterns, improving the coercive field H* and squareness while allowing the stack to maintain multiple patterns for sufficient magnetic field strength. The growth layer acts as a buffer that prevents the deterioration of H* that would otherwise occur with increased pattern stacking.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the physical and chemical parameters of the interface between antiferromagnetic layers by introducing a growth layer. This modifies the exchange coupling characteristics and improves the coercive field H* and squareness. By controlling the thickness and material composition of the growth layer, the magnetic properties of the permanent magnet are optimized to maintain H* far from the ordinate axis even with multiple patterns.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If growth layers are introduced between antiferromagnetic layers to improve coercive field H*, then H* and squareness are enhanced, but the total volume of growth layers should be limited to avoid increased complexity

Engineering Contradiction:

Improvecoercive field H* and squarenessVSAvoidstack structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of introducing growth layers between all antiferromagnetic layers in the stack, the invention applies growth layers selectively and partially. The total volume of growth layers is limited to a small percentage of the stack, yet this partial application is sufficient to improve the coercive field H* and squareness. This approach achieves the desired magnetic property enhancement without proportionally increasing the complexity of the stack structure.

Inventive Principle:

Principle #16Partial or excessive action

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 introduction of growth layers enhances the coercive field H* and squareness, leading to improved insensitivity to external magnetic perturbations and better dynamic performance of magnetic field sensors by maintaining H* further away from the ordinate axis.

Implementation Method 1

a ferromagnetic layer situated between the bottom and top antiferromagnetic layers and whose direction of magnetization is frozen, by an exchange coupling, with the bottom or top antiferromagnetic layer of this pattern

Methodology Applied

Scientific EffectExchange coupling:

Implementation Method 2

each pattern comprising: a bottom antiferromagnetic layer, a top antiferromagnetic layer, and a ferromagnetic layer situated between the bottom and top antiferromagnetic layers

Methodology Applied

Scientific EffectFerromagnetism: Ferromagnetism

Implementation Method 3

using materials like tantalum and RKKY coupling to enhance the magnetic properties

Methodology Applied

Scientific EffectRKKY coupling:

Data Source

PatentUS10643788B2Permanent magnet comprising a stack of N patterns

Publication Date: 2020.05.05 COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES

AI summary

A permanent magnet including, at least once per group of ten consecutive ferromagnetic layers, a growth layer directly interposed between a top antiferromagnetic layer of a previous pattern and a bottom antiferromagnetic layer of a following pattern. This growth layer is entirely realized in a nonmagnetic material chosen from the group made up of the following metals: Ta, Cu, Ru, V, Mo, Hf, Mg, NiCr and NiFeCr, or it is realized by a stack of several sublayers of nonmagnetic material disposed immediately on one another, at least one of these sublayers being entirely realized in a material chosen from the group. The thickness of the growth layer is greater than 0.5 nm.