The squareness of the magnet is an important indicator for measuring the performance of magnetic materials, particularly significant in the application of high-performance magnetic materials.
Definition of Squareness of The Magnet
The squareness of the magnet is a key parameter for measuring the shape of the demagnetization curve of permanent magnetic materials, primarily used to assess the magnetic performance stability of magnets under various magnetic field conditions. The specific meanings are as follows:
The squareness of the magnet (usually denoted as q) refers to the ratio of the intrinsic coercive force at the knee point of the demagnetization curve (hk) to the intrinsic coercive force (hcj), expressed as q = hk/hcj.
The closer the value of q is to 1, the more rectangular the demagnetization curve is, indicating that the magnet can maintain high stability of magnetic performance before reaching hk. This means that under normal working conditions, even with some reverse magnetic field interference, the decline rate of the magnetic induction strength (b) or magnetic polarization strength (j) is slow. The magnetic performance will only undergo rapid and irreversible demagnetization when the external magnetic field exceeds hk.
If the q value is low (far from 1), the shape of the demagnetization curve is closer to a curve, indicating that the magnet begins to demagnetize rapidly under relatively low reverse magnetic field conditions, leading to poor magnetic performance stability.
Meaning of Intrinsic Coercive Force
Intrinsic coercive force (Hcj) is an important physical quantity used to measure a magnet’s resistance to demagnetization. It refers to the intensity of the reverse magnetic field required to reduce the magnet’s remanence (Br) to zero. In simpler terms, it is the intensity of the reverse magnetic field corresponding to when the vector sum of the internal microscopic magnetic dipole moments of the magnet equals zero.
The intrinsic coercive force reflects the magnet’s ability to resist demagnetization caused by external factors (such as reverse magnetic fields, high temperatures, etc.). The greater the intrinsic coercive force, the stronger the magnet’s resistance to demagnetization, and the more stable its magnetism, particularly in high-temperature or strong reverse magnetic field environments where magnets with high intrinsic coercive forces can better maintain their magnetic performance.
Meaning of the Knee Point
From the graph, it is apparent that as the external magnetic field increases, the decline of the magnet’s magnetic induction strength/magnetic polarization strength is very slow. However, once the external magnetic field exceeds a certain value, the magnetic induction strength of the magnet will drop rapidly.
Typically, points on the demagnetization curve where Ji = 0.9Br or 0.8Br are referred to as the bending point or knee point of the demagnetization curve, corresponding to the magnetic field of Hk, also known as the knee coercive force.
Influencing Factors of Squareness Of The Magnet
| Rare Earth Element Content: For rare earth permanent magnet materials such as neodymium iron boron, the content and ratio of rare earth elements (like neodymium, dysprosium, terbium, etc.) significantly influence the squareness of the magnet. Properly increasing the content of rare earth elements can enhance the intrinsic coercive force (Hcj), thereby affecting the shape of the demagnetization curve and making the squareness of the magnet closer to the ideal value.
| Orientation Process: In the manufacturing process of magnets, by orienting the magnetic particles in alignment with the magnetic field, the remanence and coercive force of the magnet can be improved, consequently enhancing the squareness of the demagnetization curve. Factors such as the strength, direction, and uniformity of the orientation magnetic field will affect the orientation effect, thus impacting the squareness of the magnet.
| Grain Size and Distribution: Magnets with uniform grain size and reasonable distribution have a more stable magnetic domain structure, and during demagnetization, the rotation of magnetic moments and movement of magnetic domain walls are more orderly, resulting in a higher squareness of the magnet. If the grains grow abnormally long or large grains exist, it may lead to uneven magnetic performance, lowering the squareness of the magnet.
Applications of The Squareness Of The Magnet
| Wind Power Generation: The permanent magnet synchronous generators of wind turbines need to operate stably in a wide temperature range and high vibration environments. High squareness of the magnet can improve the efficiency and reliability of the generator, reducing energy losses due to magnetic field fluctuations, thereby enhancing power generation efficiency and lowering maintenance costs.
| Electric Motors: In permanent magnet motors, magnets with high squareness can maintain more stable magnetic performance under different loads and conditions. For example, the drive motors of electric vehicles need to operate efficiently under complex road conditions and temperature variations; high squareness of the magnet ensures that the motor efficiency curve is flatter, reducing efficiency losses due to magnetic field fluctuations and extending the driving range.
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