Due to their excellent magnetic properties, neodymium magnets have been widely used in electronic devices, the automotive industry, and other fields. Do you know the factors that affect the magnetic performance of neodymium magnets?
What Parameters Measure the Magnetic Properties of Neodymium Magnets?
We generally use remanence, coercivity, and maximum energy product to measure the magnetic properties of neodymium magnets.
Remanence (Br)
After a neodymium magnet is magnetized to saturation in an external magnetic field, the residual magnetic induction intensity when the external magnetic field is reduced to zero is called remanence. The unit is usually millitesla (mT) or kilogauss (kGs), where 1 tesla = 10,000 gauss.
Coercivity (Hcb) & Intrinsic Coercivity (Hcj)
Coercivity refers to the reverse magnetic field strength required to reduce the remanent induction (Br) to zero after a neodymium magnet is saturated. The unit is amperes per meter (A/m) or oersteds (Oe), with the conversion relationship of 1 A/m = (4π/1000) Oe.
Intrinsic coercivity differs from coercivity (Hcb). When the reverse magnetic field H = Hcb, the external magnetic induction intensity is zero, but the residual magnetization intensity (Br) of the magnet is not zero. It only indicates that the applied reverse magnetic field cancels out the effect of Br. When the reverse magnetic field H = Hcj, the residual magnetization intensity of the magnet drops to zero, indicating that the permanent magnet has truly demagnetized.
Maximum Energy Product (BH)max
The maximum energy product (BH)max represents the magnetic energy density established by the magnet in the space between its two poles, which is the maximum value of the product of B and H (unit: kJ/m³ or GOe). It directly indicates the performance level of the magnet.
Factors Affecting the Magnetic Performance of Neodymium Magnets
Raw Material Composition
Neodymium magnets are magnetic materials made from rare earth metal neodymium, pure iron, and boron through powder metallurgy. Other elements can be added to the ternary Nd-Fe-B material to enhance the magnetic properties of neodymium magnets further. However, the impact of these elements on the magnetic performance of neodymium magnets can be dual and should be determined based on the specific performance requirements for the application.
Neodymium: The higher the content of neodymium, the higher the remanence.
Heavy Rare Earth Elements: The higher the content of heavy rare earth metal ( Terbium / Dysprosium ) in the raw materials, the higher the Hcj (intrinsic coercive force).
Neo Magnet Production Processes
New technologies and processes constantly emerge to produce high-performance neodymium permanent magnets. During the Neo magnet production processes, the main issues are preventing the precipitation of the α-Fe phase and the oxidation of the alloy, which hinder achieving an ideal microstructure. To enhance the magnetic performance of neodymium magnets, magnet producers continuously develop new production processes, such as adding antioxidants/lubricants and using the strip casting method to make magnets.
Antioxidants: The primary benefit of adding antioxidants is reducing the oxygen content of the final magnet, allowing finer grinding of magnetic powder, which helps improve coercivity. Compared to traditional processes, adding antioxidants can increase intrinsic coercivity by about 160 kA/m.
Lubricants: Adding lubricants reduces friction between magnetic powders, improves powder fluidity, and enhances orientation, thereby increasing the remanence and magnetic performance of neodymium magnets.
Strip Casting: Producing NdFeB with a thickness of 0.25–0.35 mm using the strip casting method can eliminate the α-Fe phase. The powder made by this method has enhanced oxidation resistance, smaller grain size, and significantly improved coercivity.
External Environment
Temperature: Neodymium magnets have strict operational temperature limits. If the environmental temperature exceeds this limit, the magnet may undergo demagnetization. When the temperature surpasses the Curie temperature, the magnet’s demagnetization becomes irreversible.
Humidity: Neodymium magnets, made through powder metallurgy, have an internal structure with voids and a high iron content, making them prone to rust. Therefore, neodymium magnets are typically coated for corrosion protection. The drier the environment, the longer the magnetic performance of neodymium magnets will last.
External Magnetic Fields: If other magnetic fields influence the magnet, they can weaken its magnetic force. This is because external magnetic fields can cause the magnetic domains within the magnet to realign. If these realigned magnetic domains are not perfectly aligned, the magnetic performance of neodymium magnets will weaken.
Image Source: Smk-magnet & Hsmagnets & Researchgate & Stanfordmagnet
