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Sintered NdFeB Magnets are anisotropic

# Sintered NdFeB Magnets are anisotropic

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[Abstract]:
The sintered NdFeB permanent magnet is an anisotropic magnet.

The sintered NdFeB permanent magnet is an anisotropic magnet.

Orientation direction: The direction in which an anisotropic magnet can obtain the best magnetic properties is called the orientation direction of the magnet. Also known as "orientation axis", "easy magnetization axis". · Hysteresis loop: The closed curve of the magnetic induction (abscissa) relative to the magnetic field strength (ordinate) obtained when the ferromagnetic material undergoes periodic changes in magnetization, demagnetization, reverse magnetization, and demagnetization. .

Demagnetization curve (ie B-H curve): In the hysteresis loop, the part in the second quadrant is called the demagnetization curve. That is, we call the curve of B-H. As shown in the figure: • Knee point of the demagnetization curve: A point at which a sudden change in the demagnetization curve of the magnet occurs. A magnet with a linear demagnetization curve at room temperature will have a knee point when the temperature rises to a certain level. If the operating point of the magnet is below the knee point, the magnet will produce irreversible losses when operating in the dynamic magnetic circuit.

· Load line: A line connecting the working point and the origin of the demagnetization curve coordinate (see the figure above). Magnetization: The vector of the magnetic moments per unit volume of the material, expressed in M, in am/m (A/m).

Magnetic induction: The magnetic induction B is defined as: B = μ0 (H + M), where H and M are magnetization and magnetic field strength, respectively, and μ0 is vacuum permeability. The magnetic induction is also called the magnetic flux density, that is, the magnetic flux per unit area. The unit is Tesla (T). The unit in the CGS unit system is Gauss.

Magnetic flux: The total magnetic induction in a given area. When the magnetic induction B is uniformly distributed on the surface A of the magnet, the general formula of the magnetic flux is ? = B × A. The SI unit of flux is Maxwell.

• Leakage flux: The portion of the flux that is not leaking through the working air gap in the magnet circuit.

·Magnetic field strength: Refers to the size of the magnetic field somewhere in space. It is represented by H, and its unit is ampere/meter (A/m).

Relative magnetic permeability: The ratio of the dielectric permeability to the vacuum permeability, ie μr = μ/μo. In the CGS unit system, μo=1. In addition, the permeability of air tends to be 1 in actual use.

Magnetic Conductance: The ratio of magnetic flux Φ to magnetomotive force F, similar to the conductance in a circuit. It is a physical quantity that reflects the magnetic permeability of a material.

Permeability, Pc: is the permeability, the ratio of the magnetic induction Bd to its magnetization, ie Pc = Bd/Hd. That is what we call the "load line" or the working point of the magnet. Magnetic permeability can be used to measure how easily a magnetic material is magnetized, or how sensitive the material is to an external magnetic field. The permeability can be used to estimate the flux value under various conditions. In the magnetic circuit, there is approximately: Bd / Hd = lm / Lg, where lm is the length of the magnet; Lg is the length of the corresponding air gap of the magnet. Therefore, Pc is an important physical quantity in the design of magnetic circuits.

Curie temperature: For all magnetic materials, it is not magnetic at any temperature. Generally, the magnetic material has a critical temperature Tc above which the arrangement of the atomic magnetic moments changes from ordered to disorder due to the intense thermal motion of the atoms at high temperatures. Below this temperature, the atomic magnetic moments are aligned, resulting in spontaneous magnetization, and the material is ferromagnetic.

Magnetic circuit: The circuit through which magnetic flux flows is called a magnetic circuit. The permanent magnet and the yoke, the air gap, the pole piece and the like constitute a closed magnetic circuit.

Air gap: The gap portion of the magnetic circuit with a magnetic permeability of 1, generally an air gap, but other media.

• Air gap length - Lg: The length of the air gap in the magnetic circuit.

Magnetic Potential -F: It is the difference in magnetic potential between any two points in the magnetic circuit, similar to the voltage in the circuit.

• Magnetoresistance - R: The ratio of magnetomotive force to flux is called magnetoresistance, ie R = F /? (similar to Ohm's law), where F is the magnetomotive force and ? is the flux (CGS unit system). Similar to the resistance in the circuit.

• Yoke: A material of high magnetic permeability placed in the center of a magnet circuit or two poles that directs magnetic lines of force to reduce flux loss, typically soft magnets, pure iron or low carbon steel.

• pole piece: A ferromagnetic material placed at the magnetic pole to constrain the distribution of the magnetic flux and change its direction of flow.

• Eddy current: When the magnetic field changes, the circulating current generated in the conduction current is called eddy current. Eddy currents can generate a reverse magnetic field. Eddy currents are detrimental to rotational speed or most other magnetic circuit designs, so eddy currents should be minimized.

Magnetic saturation: Any magnetically permeable material can reach saturation under certain conditions. Ferromagnetic materials are saturated when they are magnetized. The magnetic saturation of steel is 16,000 to 20,000 Gauss.

· Stability: It is a physical quantity that measures the anti-demagnetization ability of a magnet; factors affecting the stability of a magnet are temperature or an external magnetic field.

Reversible temperature coefficient: A physical quantity that measures the reversible change in magnetic properties caused by temperature changes