Sm-Fe-N Magnet Coercivity Retention via Dual-Layer Coating

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Solution Overview

Problem

The coercivity of Sm—Fe—N magnets significantly decreases during the sintering process, resulting in magnetic properties that are lower than those of the Sm—Fe—N powder, despite existing countermeasures being insufficient.

Innovation Solution

A coating layer comprising a first layer of α-Fe and a second layer of Sm—Fe—Zn alloy is applied to the Sm—Fe—N particles, with the Zn content in the second layer ranging from 1 to 20 at %, to maintain high coercivity comparable to the powder.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If Sm—Fe—N powder is sintered at high temperature to manufacture magnet, then magnetic properties can be achieved, but coercivity deteriorates significantly

Engineering Contradiction:

Improvemagnetic propertiesVSAvoidcoercivity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

A coating layer is formed on the Sm—Fe—N powder surface before sintering to prevent coercivity deterioration during the subsequent high-temperature sintering process. The coating layer acts as a protective barrier that maintains magnetic properties throughout manufacturing.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention uses a composite coating structure with multiple layers (including α-Fe, Sm—Fe—Zn alloy, and other functional layers) applied to the Sm—Fe—N powder. This composite coating provides both protection during sintering and maintains high coercivity in the final magnet product.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If conventional coating methods are used to suppress coercivity reduction, then some protection is achieved, but coercivity is still lower than powder coercivity

Engineering Contradiction:

Improvecoercivity retentionVSAvoidcoercivity compared to powder

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The coating layer is designed with different functional layers having specific local properties: an α-Fe layer for magnetic property maintenance, a Sm—Fe—Zn alloy layer for surface protection, and controlled thickness distributions. This localized functional differentiation ensures both coercivity retention and overall magnet reliability.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention optimizes specific parameters including Zn content (1-20 at %), coating layer thickness (5-50 nm), and compositional ratios to achieve the desired coercivity retention. These parameter optimizations ensure the magnet maintains coercivity at 90% or more of the powder coercivity.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20230043317A1Sm-Fe-N MAGNET

Publication Date: 2023.02.09 TDK CORP

AI summary

A Sm—Fe—N magnet includes Sm—Fe—N particles each having a surface, a coating layer being provided on at least a portion of the surface or on at least a portion of an interface between at least two of the Sm—Fe—N particles, or being provided on both, wherein the coating layer includes a first layer and a second layer, the first layer being situated closer to the surface or the interface than is the second layer, he first layer includes α-Fe, the second layer includes a Sm—Fe—Zn alloy, and a Zn content contained in the second layer is 1 at % or more and 20 at % or less.