Curie temperature and working temperature of magnetic steel
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When it comes to the relationship between temperature and magnetism, we first need to understand a concept - the Curie temperature. Do you feel familiar hearing the words Curie? This concept does have some connection with Madame Curie. More than 200 years ago, a famous physicist discovered a physical property of magnets in his laboratory, which is that when a magnet is heated to a certain temperature, its original magnetism disappears. This great physicist was Marie Curie's husband, Pierre Curie. Later, people called this temperature the Curie point, also known as the Curie temperature (Tc) or magnetic transition point. Definition: Curie temperature is the temperature at which a magnetic material transitions between ferromagnetic and paramagnetic materials. When the temperature is below the Curie temperature, the material becomes ferromagnetic, and when the temperature is above the Curie temperature, the material becomes paramagnetic. The height of the Curie point is related to the composition and crystal structure of the substance. Temperature higher than Curie temperature: The molecules inside the magnet move violently, the magnetic domains are destroyed, and a series of ferromagnetic properties related to the magnetic domains, such as high magnetic permeability, hysteresis loop, magnetostriction, etc., disappear completely. The magnet exhibits irreversible demagnetization phenomenon. After demagnetization, it can be magnetized again, but the magnetization voltage needs to be much higher than the voltage during the first magnetization, and the magnetic field after magnetization may not reach the original level.
The Curie temperature is of great significance in practical applications. In the selection process of magnetic materials, especially soft magnetic materials, for devices that need to maintain ferromagnetism at specific temperatures, choosing materials with appropriate Curie temperatures can improve the stability and reliability of the devices.
working temperature
Work temperature (Tw) refers to the temperature range that a magnet can withstand in practical applications. Different substances have different working temperatures due to their varying thermal stability. The maximum working temperature of magnetic steel is much lower than the Curie temperature. Within the working temperature, the magnetic force will decrease with increasing temperature, but most of it can be restored after cooling. The relationship between working temperature and Curie temperature: The higher the Curie temperature, the higher the working temperature of the magnetic material, and the better the temperature stability. Adding elements such as cobalt, terbium, and dysprosium to sintered neodymium iron boron raw materials can increase their Curie temperature, so dysprosium is commonly present in high coercivity products (H, SH,...). The same type of magnet, different grades and grades have different temperature resistance due to differences in composition and structure. Taking neodymium iron boron as an example, the maximum working temperature of magnetic steel of different grades ranges from 80 ℃ to 230 ℃.
Several factors affecting the actual working temperature of magnetic steel: 1 The shape and size of magnetic steel (i.e. aspect ratio, also known as magnetic permeability coefficient Pc) have a significant impact on the actual maximum working temperature. Not all H-series neodymium iron boron magnetic steel can operate without demagnetization at a temperature of 120 ℃. Some sizes of magnets may be demagnetized at room temperature, so it is necessary to increase the coercive force level to improve the actual maximum working temperature. The degree of closure of the magnetic circuit also affects the actual maximum operating temperature of the magnet. The closer the working magnetic circuit of the same magnet is, the higher the maximum operating temperature of the magnet, and the more stable the performance of the magnet. So the maximum operating temperature of a magnet is not a fixed value, but varies with the degree of closure of the magnetic circuit.