1. Magnetism
Experiments shows that any substance can be more or less magnetized in an external magnetic field, just with different degrees of magnetization. According to the properties of substances in the external magnetic field, they can be classified into five classes: paramagnetic, diamagnetic, ferromagnetic, ferrimagnetic and antiferromagnetic. We call paramagnetic and diamagnetic as weak magnetic material, ferromagnetic and ferrimagnetic as strong magnetic material.

2.magnetic materials
Soft magnetic materials: the maximum magnetization can be achieved with the minimum external magnetic field, it is a magnetic material with low coercivity and high permeability. Soft magnetic materials are easy to magnetize, and easy to demagnetize. For example: soft ferrite, amorphous nanocrystal alloy.
Hard magnetic materials: also called permanent magnetic material, it refers to a material that is difficult to magnetize and difficult to demagnetize once magnetized, it is characterized by high coercivity, including rare earth permanent magnet, metal permanent magnet and permanent magnet ferrite.
Functional magnetic materials: mainly magnetostrictive materials, magnetic recording materials, magnetoresistance materials, magnetic bubble materials, magneto-optical materials and magnetic thin film materials etc.

3.NdFeB permanent magnet
Sintered NdFeb permanent magnet adopts the powder metallurgy process, the smelted alloy is made into powder and pressed in the magnetic field to make the pressed embryo, the pressed embryo are densified by sintering in an inert gas or vacuum, in order to improve the coercivity of magnets, aging heat treatment is usually required, and the finished products are obtained after processing and surface treatment.
Bonded NdFeB is a permanent magnetic powder mixed with rubber with good winding ability or hard and light weight plastic,rubber and other bonding materials, it’s directly molded into permanent magnetic parts of various shapes according to customer requirements.
Hot-pressing NdFeb can achieve magnetic properties similar to NdFeB without adding rare earth elements, it has the advantages of high density, high orientation, good corrosion resistance, high coercivity and near final molding, but the mechanical properties are poor and the processing cost is high due to patent monopoly.

4. remanence Br
The remanence refers to the magnetic induction intensity of sintered NdFeB magnet when a magnet is magnetized by external magnetic field in closed circuit environment to the technology saturation and then the magnetic field is withdrawn. Generally speaking, it can be briefly understood as the magnetic force of the magnet after magnetization. The units are Tesla and Gauss, 1Gs=0.0001T.

5. Coercivity Hcb
When a magnet is magnetized in reverse, the value of reverse magnetic intensity induction required to reduce the magnetic induction intensity to zero is called magnetic intensity coercivity. However, the magnetization of the magnet is not zero at this time, but the added reverse magnetic field cancels with the magnetization of the magnet, at this time, if the external magnetic field is withdrawn, the magnet still has certain magnetic performance.
1A/m=(4π/1000)Oe, 1 Oe =(1000/4π) A/m。

6.Intrinsic coercivity, Hcj
The reverse magnetic field strength required to reduce the magnetization of a magnet to zero is called intrinsic coercivity. Magnetic materials are classified according to the size of their intrinsic coercivity force. Low coercivity force N, middle coercivity force M, high coercivity H, extremely high coercivity UH, very high coercivity EH, supreme coercivity TH.

7. (BH)max
Represents the magnetic energy density established by the two magnetic poles of a magnet, that is magnetostatic energy per unit volume of air gap, is the maximum of the product of Br and Hcj, its size directly indicates the performance of magnet. Under the same conditions, namely the same size, the same number of poles and the same magnetization voltage, the magnetization table of magnetic parts with high magnetic energy product is also high, however, at the same (BH)max value, the height of Br and Hcj has the following effects on the magnetization:
Br high, Hcj low, under the same magnetizing voltage, a higher surface magnetism can be obtained.
Br low, Hcj high, if get , a higher magnetizing voltage is required to obtain the same surface magnetism.

8.SI system and CGS system
Namely international unit system and gauss unit system, it’s like the difference between meters and li in units of length . There is a complex conversion relationship between the international system of units and the gauss system of units.

9.Curie temperature
The temperature at which a magnetic material changes between a ferromagnet and a paramagnetic substance, the material becomes a ferromagnet when it’s below the Curie temperature, the magnetic field associated with the material is difficult to change. The material becomes a paramagnetic substance when the temperature is higher than the Curie temperature, and the magnetic filed of the magnet is easily changed by changes by changes in the surrounding magnetic field.
The Curie temperature represents the theory working temperature limitation of magnetic materials, the Curie temperature of NdFeB is about 320-380 degree Celsius, the Curie point is related to the crystal structure formed by sintering with magnets. If the temperature reaches Curie temperature, the molecules inside the magnet will move violently and demagnetize, which is irreversible. After demagnetization, the magnet can be magnetized again, but its magnetism will be greatly reduced, only to about 50% of its original strength.

10.Working temperature
The highest working temperature of sintered NdFeb is far lower than its Curie temperature, the magnetic force will decrease if the temperature rises with the working temperature, but most of the magnetic force will recover after cooling.
Relationship between working temperature and Curie temperature: the higher the Curie temperature is, the higher the magnetic working temperature is and the better the temperature stability is. The addition of cobalt,terbium, dysprosium and any other elements into sintered NdFeB raw material can increase its Curie temperature, Consequently, high coercivity products(H,SH...) dysprosium is ubiquitously contained. The highest temperature of sintered NdFeb depends on its magnetic performance and working point. For the same sintered NdFeb magnet, the more closed the working magnetic circuit, the higher the maximum operating temperature of the magnet, the more stable the performance of the magnet. Therefore, the maximum operating temperature of a magnet is not a certain value, but varies with the degree of closure of the magnetic circuit.

11.The magnetic field orientation
Magnetic materials can be divided into isotropic and anisotropic magnets. Isotropic magnets have the same magnetic property in any direction and can be suck together at will; anisotropic magnets have different magnetic properties in different directions, and the direction in which they can obtain the best magnetic properties is called the orientation direction of the magnet.
A square sintered NdFeb magnet has the strongest magnetic field only in the orientation direction, the other two directions are much weaker. Magnetic material is in the production process if there is a orientated process is an anisotropic magnet, sintered NdFeb is generally formed by magnetic field orientation, so that’s anisotropic, therefore we need to determine the orientation direction before production, the coming direction of magnetization. Powder magnetic field orientation is one of the key technologies to produce high performance NdFeb.(Bonded NdFeb is isotropic or anisotropic.)

12.Surface magnetic field
Refers to the magnetic induction intensity at a point on the surface of a magnet(the surface magnetism at the center of a magnet is different from that at the edge), is the value measured by gauss meter in contact with a surface of the magnet, not the overall magnetic performance of the magnet.

13.Magnetic flux
Set in a uniform magnetic field with magnetic intensity induction B, there is a area of S and and a plane perpendicular to the direction of the magnetic field, the product of magnetic induction intensity B and the area S, called through the planar magnetic flux, hereinafter referred to as flux,the symbol is “Φ”，the unit is Wb. Magnetic flux is a physical quantity that represents the distribution of magnetic field, it’s a scalar quantity, but it has plus or minus, plus or minus just represents its direction.Φ=B·S，when there is an angle θ between the vertical plane of S and B, Φ=B·S·cosθ。

14.Plating
NdFeb was produced by powder metallurgy technology, is a kind of very strong chemical activity of powder materials, within tiny pore and holes, easy corrosion and oxidation in the air, and so before use must be strict surface treatment, plating as a mature means of metal surface treatment which has been widely applied.
The most commonly used coatings for NdFeb strong magnets are zinc plating and nickel plating, they have obvious differences in appearance, anti-corrosion, service life,price and other aspects:
Polishing difference: Ni coated is superior to zinc coated on polish, it’s a little bit brighter than outside. Generally, those with high reuqirements for the appearance of the product will choose Ni coated, and some magnets are not exposed, relatively low requirements for the appearance of the product will choose zinc coated.
Corrosion resistance distinction: zinc is an active metal, it reacts with acids, so corrosion resistance is poorer; after the surface treatment of nickel plating, its corrosion resistance is higher.
Service life distinction: Because of the corrosion resistance is different, the service life of zinc coated is lower than ni coated, mainly in the use of a long time surface plating is easy to fall off, leading to the oxidation of magnets, thus affecting the magnetic properties.
Hardness distinction: ni coated is higher than zinc coated, in the process of use, it can avoid collision to a great extent, resulting in the NdFeb strong magnet angular loss, fragmentation and other phenomena.
Price distinction: zinc coated is extremely advantageous in this respect, the price from low to high for galvanized: zinc coated, ni coated, epoxy resin and so on.

15.Single magnet
Magnets all have two poles, but in some working locations, need single-pole magnets are needed, so it is necessary to cover one side of the magnet with an iron sheet, so that the magnetism of the side covered by the iron sheet is shielded. Such magnets are collectively called single-side magnets. There are no real single-sided magnets.