Coercive force refers tomagnetic material After saturation magnetization, when the external magnetic field returns to zeroMagnetic inductionBNot back to zero, only in the originalMagnetizing fieldAdd a certain size in the opposite directionmagnetic fieldTo make magnetic inductionstrengthWhen the magnetic field returns to zero, it is called coercive magnetic field, also called coercive force.[1]
The intensity of external magnetic field that must be applied in the opposite direction to the original magnetization to make the magnetized ferromagnetic material lose its magnetism.It is not only related to the properties of ferromagnetic materials, but also depends on the original magnetization of ferromagnetic materials.When manufacturing the iron core or electromagnet of the transformer, it is necessary to select materials with low coercivity (such as soft iron, silicon steel, etc.) to make the magnetism disappear as soon as possible after the current is cut off.When manufacturing permanent magnets, it is necessary to select materials with high coercivity (such as aluminum, nickel, cobalt, etc.) in order to preserve the magnetism as much as possible and not make it disappear.[2]
Hysteresis loop generation
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Hysteresis loop
stayPermanent magnetic materialOfDemagnetization curveWhen the reverse magnetic field increases to a certain valueHCWhen,magnetMagnetic induction intensity ofBIs 0, and the reverse magnetic field is called the coercivity of the materialHC；When the reverse magnetic field isHCWhen, the magnet is not displayed externallyflux, so coercivityHCCharacterization of permanent magnetic materialsresistanceThe ability of external reverse magnetic field or other demagnetization effects.HCIs an important part of the magnetic circuit designparameterone of.
For coercivityHCRepresentation (This representation often refers toB=0）。According to the magnetic induction intensityBAndmagnetic field intensityHandMagnetizationMRelationship ofB=μzero(H+M）, if orderedB=0, getHC=－M。WhenM=0, getHC=B/μzero；CommonBHCandMHCTo show the difference.MHC>BHC，M=The value given by 0 is called the internal coercivity.[1]
characteristic
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CoercivityHCAlways less than in valueremanenceBr。stayHC,B=0 onDemagnetization curveAt any point onMagnetic polarization intensityValue is always less than remanenceBr, soHCIt is always less than remanence in valueBr。For example:Br=12.3KGs magnet, whichHCIt cannot be greater than 12.3KGs.In other words, remanenceBrIs numerically coerciveHCTheory oflimit。[1]
influence factor
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Among the magnetic properties, the coercivity is most strongly affected by the change of grain size.For the roughly spherical grains, the coercivity increases with the decrease of the grain size. After reaching a maximum value, the coercivity decreases with the further decrease of the grains.The grain size corresponding to the maximum coercivity is equivalent to the size of a single domain. For different alloy systems, the size range is from ten to several hundred nanometers.When the grain size is larger than the single time size, the coercivity HcThe relationship with the average grain size D is:
Where C is a constant related to the material.It can be seen that when the grain size of nano materials is larger than the single deformed size, the coercivity also increases with the decrease of grain size D.[3]
At the same time, because the coercivity comes from irreversibilityMagnetization processTherefore, the main factor causing the irreversible magnetization mechanism is the presence ofMagnetic anisotropy(including magnetocrystallineInductionandstressetc.anisotropy）Impurities, pores, defects and other factors will also affect the coercivity.[1]
