What is the coercive force (bHc), what is the intrinsic coercivity (jHc)?
On the demagnetization curve of permanent magnet material, when a reverse magnetic field H is increased to a value bHc, magnetic induction B magnets is zero, saying that the reverse magnetic field H is the coercive force of the material bHc; in reverse When the magnetic field H = bHc, does not display the external magnet flux, therefore bHc coercivity magnetic materials characterization capability, or other external reverse magnetic field demagnetization resistance. BHc coercive force is one of the important parameters of magnetic circuit design.
It is worth noting: coercivity bHc the value is always less than the residual magnetism Jr. Because from the (1-1) can be seen in the H = bHc place, B = 0, then μ0 bHc = J, has been explained above, in the magnetic polarization J demagnetization curve at any point is always less than the value of the residual magnetization Jr , so the coercive force bHc in value is always less than the residual magnetism Jr. For example: Jr = 12.3kGs magnets, which bHc not be greater than 12.3kOe. In other words, the residual magnetization Jr in value is the theoretical limit of the coercive force bHc.
When the reverse magnetic field H = bHc time, although the magnetic induction of the magnet B 0, do not display the external magnet flux, but the magnet inside the microscopic magnetic dipole moment vector and often not to zero, which means that at this time the magnet magnetic intensity J in the original direction often remain a large value. Therefore, bHc not enough to characterize the intrinsic magnetic properties of the magnet; when the reverse magnetic field H is increased to a value jHc, the magnet inside the microscopic magnetic dipole moment vector and 0, said the value of the reverse magnetic field H The material of the intrinsic coercivity jHc.
JHc intrinsic coercivity is a very important physical parameters of permanent magnet materials, much greater than for jHc bHc magnet, the magnetic field H is greater than when the reverse bHc but less than jHc, although this time the magnet has been demagnetization to the magnetic induction B anti- to the extent, but in the reverse magnetic field H revoked magnet magnetic induction B still due to internal microscopic magnetic dipole moment vector and in the original direction and return to the original direction. That is, as long as the reverse magnetic field H has not yet reached jHc, permanent magnetic materials will not yet be fully demagnetization. Thus, the intrinsic coercivity magnetic materials jHc characterize reverse against external magnetic fields or other demagnetization effects, in order to maintain a major indicator of the ability of the state to its original magnetization.
BHc same coercive force and intrinsic coercivity and magnetic field strength units jHc units.
General magnetic properties can be expressed through its four parameters, namely, the residual magnetic flux density (hereinafter referred to remanence) Br (Gauss unit Gs or Milliteslameter mT, 1mT = 10Gs), the coercive force Hcb (unit Auster Oe) , intrinsic coercivity Hcj (unit Oster Oe), the maximum energy product (BH) max (unit mega high Austria MGOe), which Br, Hcj, (BH) max is the most direct three-parameter representation.
Relationship Br, Hcj, (BH) max of the three
Br size is generally thought to indicate magnetic pieces magnetizing the surface of the magnetic field level; Hcj may indicate the size of the magnetic member after magnetization and demagnetization resistance to high and low temperature; (BH) max is the maximum value of the product Br and Hcj Its size is directly indicates the performance level of the magnet. At present we have not detected bonded NdFeB (BH) max can be greater than 11.5 magnet.
In general, (BH) max similar magnet, Br high, Hcj on the low side; Hcj high, Br on the low side. We can not just order (BH) max to determine the level of quality of the product, but also the level of Br and Hcj suitability of the products we need.
Three sizes are described in the quality of material
We can not Br, Hcj, (BH) max to determine the level of its good or bad, you want to use the product, the required characteristics to determine the level of the three; even under conditions equivalent (BH) max value, but also look at the product's use, magnetizing requirements to determine with high Br value, low Hcj, or vice versa.
Effect of three sizes of magnetized
As we all know, under the same conditions, that is the same size magnetic table, the same number of poles and the same magnetizing voltage, high energy product magnetic member obtained is also high, but at the same time (BH) max values, Br and Hcj The level of magnetization has the following effects:
Br high, Hcj low: at the same magnetizing voltage, can obtain high magnetic table;
Br low, Hcj high: To get the same table magnetic, magnetizing the higher voltage required;
For a multi-polar magnetic charge, to adopt a low magnetic Hcj Br high, and for magnetic tile, the general Hcj high Br low magnetic powder, which is used as the motor magnetic tile, in use, to bear a larger demagnetization current and overload.