1. Remanence (Br)
• Definition: Remanence refers to the magnetic induction intensity that remains inside a magnetic material when the external magnetic field strength is reduced to zero after the material has been magnetized to saturation by an external magnetic field. It directly reflects the magnitude of the magnetism that the material can retain after being magnetized. For example, Nd-Fe-B permanent magnet materials have a relatively high remanence, which enables them to maintain strong magnetism even after the external magnetization field disappears. Thus, they can be used to manufacture high-performance permanent magnet motors and other equipment.
• Unit: It is usually expressed in tesla (T) or gauss (Gs). In the International System of Units, 1 T = 10,000 Gs.
• Influence: Remanence has a significant impact on the performance of magnets in practical applications. Magnets with high remanence can generate a strong magnetic field over a long distance, which is crucial for application scenarios requiring the action of a magnetic field over a long distance, such as magnetic separation equipment for ore dressing. Meanwhile, in the field of magnetic recording, materials with high remanence can store information more effectively because they can generate a stronger local magnetic field to change the magnetic state of the magnetic recording medium.
2. Coercive force (Hc)
• Definition: Coercive force is the reverse magnetic field strength that needs to be applied to reduce the magnetic induction intensity of a magnetized magnetic material to zero. It measures the ability of the material to resist demagnetization. For instance, the magnetic materials used in the magnetic heads of hard disk drives need to have a relatively high coercive force so as to ensure that the data stored in the hard disk will not be lost due to interference from external magnetic fields in a complex electromagnetic environment.
• Unit: It has the same unit as the magnetic field strength, namely ampere per meter (A/m) or oersted (Oe). 1 A/m ≈ 0.01257 Oe.
• Influence: Magnets with high coercive force are less likely to be demagnetized when subjected to interference from external magnetic fields. In equipment like motors, during the working process, they may be affected by external alternating magnetic fields. Using magnets with high coercive force can ensure the stability of the magnetic field of the motor, thereby improving the performance and service life of the motor.
3. Maximum energy product (BH)max
• Definition: The maximum energy product is the product of the magnetic flux density (B) and the magnetic field intensity (H) at any point on the demagnetization curve. (BH)max represents the maximum value of the energy product and reflects the ability of magnetic materials to store magnetic energy. Briefly speaking, the higher the maximum energy product, the greater the magnetic field energy that a magnet can provide under the same volume.
• Unit: Joule per cubic meter (J/m³).
• Influence: When designing permanent magnet motors, speakers and other equipment, the maximum energy product is a crucial parameter. Magnets with a high maximum energy product can provide a sufficiently powerful magnetic field in a smaller volume, which helps to reduce the size and weight of the equipment while improving its performance. For example, in miniaturized speakers, using magnets with a high maximum energy product can make the speakers more compact and portable without degrading the sound quality.
4. Curie temperature (Tc)
• Definition: The Curie temperature refers to the temperature at which the magnetism of a magnetic material changes abruptly. When the temperature rises to the Curie temperature, the magnetism of the magnetic material will drop sharply, changing from ferromagnetic or ferrimagnetic to paramagnetic. For example, the Curie temperature of Nd-Fe-B magnets is generally around 310 - 350 °C. When the temperature approaches or exceeds this range, its magnetism will weaken rapidly.
• Unit: Degree Celsius (°C).
• Influence: The Curie temperature limits the working temperature range of magnets. For equipment working in high-temperature environments, such as sensors near car engines or magnets in motors, it is necessary to choose magnetic materials with a relatively high Curie temperature to ensure that the equipment can still work normally under high temperatures. Otherwise, once the temperature exceeds the Curie temperature, the magnetism of the magnets will decline, resulting in a decline in equipment performance or even failure.
5. Temperature coefficient (α)
• Definition: The temperature coefficient is a parameter used to describe how the magnetism of a magnetic material changes with temperature. It represents the relative change rate of a certain magnetic parameter (such as remanence, coercive force, etc.) of the magnetic material per 1 °C change in temperature within a certain temperature range. For example, for some magnets, the temperature coefficient of remanence may be -0.12%/°C, which means that for every 1 °C increase in temperature, the remanence will decrease by 0.12%.
• Unit: Generally, it is percentage per degree Celsius (%/°C).
• Influence: The temperature coefficient is very important for applications of magnets that need to work in environments with temperature changes. By knowing the temperature coefficient, we can predict the performance changes of magnets at different temperatures, and then take corresponding measures, such as choosing materials with a small temperature coefficient or designing temperature compensation devices, to ensure that the equipment can work stably when the temperature changes.
