15 concepts related to magnetic materials explained-1
1.Magnetic
Experiments show that any substance can be magnetized more or less in an external magnetic field, but the degree of magnetization is different. According to the characteristics of the material in the external magnetic field, the material can be divided into five categories: paramagnetic material, diamagnetic material, ferro magnetic material, ferrimagnetic material, and antiferromagnetic material. We call paramagnetic materials and diamagnetic materials weakly magnetic materials, and call ferromagnetic materials and ferrimagnetic materials strong magnetic materials.
Soft magnetic material: The maximum magnetization can be achieved with the smallest external magnetic field. It is a magnetic material with low coercivity and high permeability. Soft magnetic materials are easy to magnetize and also easy to demagnetize. For example: soft ferrite, amorphous nanocrystalline alloy.
Hard magnetic materials: also called permanent magnetic materials, which refer to materials that are difficult to magnetize and are difficult to demagnetize once magnetized. Its main feature is high coercivity, including rare earth permanent magnetic materials, metal permanent magnetic materials and permanent ferrites .
Functional magnetic materials: mainly magnetostrictive materials, magnetic recording materials, magnetoresistance materials, magnetic bubble materials, magneto-optical materials, and magnetic thin film materials.
3. Neodymium iron boron permanent magnet material
The sintered NdFeB permanent magnet material adopts powder metallurgy technology. The smelted alloy is made into powder and pressed in a magnetic field to form a compact. The compact is sintered in an inert gas or vacuum to achieve densification, in order to improve the coercivity of the magnet , Usually requires aging heat treatment, and then after processing and surface treatment to obtain the finished product.
Bonded neodymium iron boron is made of permanent magnet powder mixed with good windability rubber or hard and light plastic, rubber and other bonding materials, and directly formed into permanent magnet parts of various shapes according to user requirements.
Hot-pressed NdFeB can achieve magnetic properties similar to sintered NdFeB without adding heavy rare earth elements, with high density, high orientation, good corrosion resistance, high coercivity and near-final molding, etc. Advantages, but the mechanical performance is not good and the processing cost is higher due to the patent monopoly.
4. Remanence Br
It refers to the magnetic induction intensity of a sintered neodymium iron boron magnet when a magnet is magnetized by an external magnetic field in a closed circuit environment until the technology is saturated and then the external magnetic field is cancelled. In layman's terms, it can be temporarily understood as the magnetic force of the magnet after magnetization. The unit is Tesla (T) and Gauss (Gs), 1Gs=0.0001T.
5. Coercivity Hcb
When the magnet is magnetized in the reverse direction, the value of the reverse magnetic field strength required to reduce the magnetic induction intensity to zero is called the magnetic coercive force. However, the magnetization of the magnet is not zero at this time, but the applied reverse magnetic field and the magnetization of the magnet cancel each other out. At this time, if the external magnetic field is removed, the magnet still has certain magnetic properties. 1A/m=(4π/1000)Oe, 1 Oe=(1000/4π) A/m.
6. Intrinsic coercivity Hcj
The strength of the reverse magnetic field required to reduce the magnetization of the magnet to zero is called the intrinsic coercivity. The classification of magnetic grades is based on their intrinsic coercivity. Low coercivity N, medium coercivity M, high coercivity H, ultra-high coercivity UH, extremely high coercivity EH, supreme coercivity TH.
7. Maximum magnetic energy product (BH)max
It represents the magnetic energy density established by the space between the two magnetic poles of the magnet, that is, the magnetostatic energy per unit volume of the air gap, which is the maximum value of the product of B and H, and its size directly indicates the performance of the magnet. Under the same conditions, that is, the same size, the same number of poles and the same magnetizing voltage, the magnetic parts with high magnetic energy product can obtain higher surface magnetism, but at the same (BH)max value, the level of Br and Hcj It has the following effects on magnetization:
High Br, low Hcj: Under the same magnetizing voltage, higher surface magnetism can be obtained;
Br is low, Hcj is high: To obtain the same surface magnetism, a higher magnetizing voltage is required.