Rare Earth Magnet Ga Concentration Gradient Coercivity
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Solution Overview
Problem
R-T-B based sintered magnets experience thermal demagnetization when exposed to high temperatures due to anti-ferromagnetic coupling between rare earth elements like Nd and Dy, leading to a decrease in coercivity, and existing methods to enhance coercivity either reduce residual magnetic flux density or are limited by the availability of heavy rare earth elements.
Innovation Solution
A rare earth magnet with main phase grains having an R2T14B type crystal structure, incorporating gallium (Ga) with a concentration ratio of 1.20 or more, and a Ga concentration gradient within the grains to enhance coercivity and restrain thermal demagnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If heavy rare earth elements (Dy, Tb) are used to enhance coercivity at room temperature, then coercivity is improved, but residual magnetic flux density decreases due to anti-ferromagnetic coupling
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of gallium within the main phase grains, where the Ga concentration varies from the grain center to the grain boundary. This spatial variation in composition allows different regions of the grain to have optimized properties: the core maintains high magnetic flux density while the boundary region enhances coercivity, thereby resolving the contradiction between residual magnetic flux density and coercivity.
2Force
If heavy rare earth elements are used to improve coercivity, then room temperature coercivity increases, but thermal demagnetization resistance decreases due to rapid temperature dependence of crystal magnetic anisotropy energy
Solution Approach 1:
The patent changes the compositional parameter by introducing gallium and creating a concentration gradient, which modifies the magnetic properties differently across the grain structure. This compositional parameter change allows the material to maintain stable coercivity across a wide temperature range by reducing the temperature dependence of crystal magnetic anisotropy energy, thereby improving thermal demagnetization resistance while maintaining room temperature coercivity.
3Force
If non-magnetic materials and soft magnetic materials are added to main phase grains to improve coercivity by pinning magnetic domain walls, then coercivity is improved, but residual magnetic flux density decreases
Solution Approach 1:
The patent uses a small amount of gallium distributed in a gradient pattern rather than adding significant quantities of non-magnetic or soft magnetic materials. This approach achieves magnetic domain wall pinning and enhanced coercivity without substantially compromising the residual magnetic flux density, as the gallium concentration is optimized to provide just enough pinning effect without creating large non-magnetic regions that would reduce overall magnetic flux.
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 magnet exhibits a reduced thermal demagnetization factor and maintains high coercivity at room temperature, even in high-temperature environments, without compromising residual magnetic flux density.
Implementation Method 1
it is pointed out that prevention of magnetic domain wall motion of a reverse magnetic domain generated is also important for improvement in coercivity of rare earth magnets
Implementation Method 2
the factor of improvement in coercivity due to use of heavy rare earth elements is improvement in crystal magnetic anisotropy energy due to use of heavy rare earth elements
Implementation Method 3
R-T-B based sintered magnets experience thermal demagnetization when exposed to high temperatures due to anti-ferromagnetic coupling between rare earth elements like Nd and Dy
Data Source
AI summary
A rare earth magnet includes main phase grains having an R2T14B type crystal structure. The main phase grains include Ga. A concentration ratio A (A=αGa/βGa) of the main phase grains is 1.20 or more, where αGa and βGa are respectively a highest concentration of Ga and a lowest concentration of Ga in one main phase grain.