Neodymium iron boron correlation curve

Demagnetization curve:

Definition: It refers to the curve in which the magnetic induction intensity B or magnetization intensity M of a permanent magnet gradually decreases with the increase of the reverse magnetic field after saturation.
Characteristic: It is approximately a straight line within a certain temperature range, but there will be a clear inflection point at high temperatures. Above the inflection point is a straight line segment, and the magnetic density rapidly decreases after the inflection point. When the working point of the permanent magnet is below the inflection point, irreversible demagnetization occurs after the external magnetic field is cancelled, and the residual magnetism after recovery is lower than the original value.
Intrinsic demagnetization curve:

Definition: It is a curve that reflects the anti demagnetization ability of neodymium iron boron materials, with magnetization intensity M as the vertical axis and magnetic field intensity H as the horizontal axis.
Meaning: Intrinsic coercivity corresponds to the reverse magnetic field strength on the intrinsic demagnetization curve that reduces the magnetization to zero. The intrinsic demagnetization curve is crucial for evaluating the stability of neodymium iron boron under extreme conditions such as high temperature or strong magnetic field.
Hysteresis loop:

Definition: When a periodically changing magnetic field is applied to neodymium iron boron material, the magnetic induction intensity B of the material will exhibit a closed curve with the variation of the magnetic field intensity H, that is, a hysteresis loop.
Characteristics: The shape and size of the hysteresis loop reflect the magnetic properties of neodymium iron boron materials, such as remanence, coercivity, magnetic energy product, etc., which can be obtained from the hysteresis loop.

High temperature parameters of neodymium iron boron

Curie temperature (Tc) 2:

Definition: The magnetic properties of neodymium iron boron magnets gradually weaken with increasing temperature until the temperature at which they lose their magnetism. The Curie temperature of neodymium iron boron is generally between 320-380 degrees Celsius.
Meaning: It determines the theoretical operating temperature limit of neodymium iron boron magnets. Beyond the Curie temperature, the internal molecules of the magnet undergo violent motion and irreversible demagnetization.
Maximum operating temperature:

At the material level, the national standard GB 13560-2017 sintered neodymium iron boron permanent magnet materials defines a permanent magnet cylindrical sample with a length to diameter ratio of L/D=0.7 in a thermally demagnetized state. After saturation magnetization, it is heated from room temperature to a constant temperature for 2 hours in an open circuit state, and then cooled to room temperature. The maximum insulation temperature at which the irreversible loss of open circuit magnetic flux is less than 5% is reached.
At the product level: Due to factors such as product shape, magnetic circuit structure, and working environment, even when using the same material grade, there will be significant differences in demagnetization of different magnetic steel products at high temperatures. Usually, the critical value of magnetic performance attenuation of magnetic steel products when working at this temperature, or when working at this temperature and cooling to room temperature, is confirmed through experiments.
Temperature coefficient:

Intrinsic coercivity temperature coefficient: generally expressed as α, usually negative, in%/℃. For example, the temperature coefficient of intrinsic coercivity of common neodymium iron boron materials is around -0.6%/℃, which means that for every 1 ℃ increase in temperature, the intrinsic coercivity decreases by approximately 0.6%.
Residual magnetic temperature coefficient: generally expressed as β, also negative, and measured in%/℃. The common remanence temperature coefficient of neodymium iron boron materials is around -0.12%/℃ to -0.13%/℃, which means that for every 1 ℃ increase in temperature, the remanence will decrease by about 0.12% -0.13%