Factors Influence the Magnetic Force of Sintered NdFeB Magnets

Grades of Sintered NdFeB Magnets

The distinction in grades of sintered NdFeB magnets primarily lies in their magnetic performance parameters, including remanence (Br), coercivity (Hcb), intrinsic coercivity (Hcj), and maximum energy product ((BH)max). Different grades of magnets have unique performance characteristics to meet varying application needs.

First, let's understand the differences in magnet grades:

Grades of sintered NdFeB magnets typically begin with the N series, followed by numbers and letters representing the temperature coefficient, such as N35, N38H, N40SH, N42UH, etc. The number represents the maximum energy product of the magnet—the higher the number, the greater the energy product, and the stronger the magnet.

The maximum energy product of permanent magnet materials is expressed in MGOe (MegaGaussOersteds). It represents the strongest point on the magnet's demagnetization curve or BH curve. In simple terms, the higher the magnet grade, the larger the magnetic field the magnet produces, which means greater magnetism.

Temperature of Sintered NdFeB Magnets

Saturation Magnetization

As the temperature rises, the saturation magnetization of sintered NdFeB magnets decreases. This is because, at higher temperatures, lattice vibrations increase, weakening the interactions between magnetic domains and reducing the degree of magnetization. This change implies that in high-temperature environments, the magnet's strength will weaken.

Coercivity Changes

Although coercivity (the material's resistance to demagnetization) may increase with rising temperatures, this does not mean an increase in magnetic strength. In fact, the increase in coercivity is due to the enhanced thermal activation effect at higher temperatures, which reduces the stability of magnetic domains, requiring a larger reverse magnetic field to achieve domain reversal. However, this change does not directly equate to an increase in magnetic force and may indirectly affect magnetic performance due to the reduced stability of magnetic domains.

Temperature Coefficient

The magnetization of sintered NdFeB magnets changes at different temperatures, determined by the temperature coefficient. Generally, the temperature coefficient for NdFeB magnets is negative, meaning that as temperature increases, magnetization decreases. This implies that in high-temperature conditions, the magnet's strength will further decline.

Working Temperature Range and Grades

Sintered NdFeB magnets are divided into different grade series based on their working temperature ranges (e.g., N, M, H, SH, UH, AH, etc.). These grades reflect the performance stability of magnets at various temperatures. Magnets with higher working temperature grades usually cost more because they require more complex manufacturing processes and material compositions to ensure performance stability at high temperatures.

Considerations in Practical Applications

In practical applications, it is necessary to select the appropriate grade of sintered NdFeB magnet based on the specific working temperature requirements. If the working environment temperature is high, choose magnets with higher working temperature grades to ensure their strength does not significantly decrease with rising temperatures. Additionally, measures can be taken to reduce the temperature's impact on magnet strength, such as optimizing the magnet structure and enhancing heat dissipation.