B-H Curve for Permanent Magnets
What is a B-H curve first of all? B is the nomenclature for magnetic flux density (induction) and H is magnetic field strength; a B-H curve plots out the relationship between them for a particular ferromagnetic material. The changes in magnetic flux density is dependent on the magnetic field strength. Such curve is generated by automatic hysteresisgraph which also defines many other aspects of a magnet material’s qualities.
Along with every custom order, we always attach the corresponding B-H curve for the exact batch of material used. In this report, you can find values of magnetic properties for Br in kGs, Hc in kOe, Hci in kOe, (BH)max in MGO, Hk in kOe, Hd in kOe, Bd in kGs and material’s chemical composition. Now let’s take a closer look at the B-H curve formation which is basically a magnetization and de-magnetization process cycle.
Start magnetization – Place a neodymium magnet at the center of a magnetizer or basically a coil of wire
Reach saturation – Pass a powerful current through the wire to create a uniform magnetic field, H. As the magnetic field strength increases, the induction increases until it levels off at Bm and Hm.
Remove the magnetic field – When the current is cut off, there is still residual magnetic induction, remanence Br, created by the saturated magnetic material without the effect of magnetization.
De-magnetization – Apply a current through the wire in the opposite direction. The magnetic flux reaches zero at a negative magnetic field, -Hc, known as the magnet’s coercivity, coercive field intensity, or its reversibility to drive the magnetization back to zero after being saturated by external magnetic field. In many cases where a strong magnetic demagnetization field exists, neodymium magnets could be used as a reversible medium for large amount of energy transformation in miniaturized application.
-7. Mirror process of above with magnetization and de-magnetization in the opposite direction as Step 1-4 where magnetic field strength and flux density increase in the opposite direction and eventually reach negative saturation and so on. The magnetization towards point 2 follow a different path as the magnet material has previously been magnetized.
And now, we have a complete hysteresis curve illustrating the behavior of a magnet. Based on the shape of the graph, engineers can then estimate the magnet’s performance which is dependent on its shape and its magnetic circuit, and select the best suitable material for a specific application. For permanent magnets, the broader B-H loops are more desirable.