What does the remanence (Br) indicate in a magnetic hysteresis loop?
It is the residual magnetic flux density after removing the applied field.
When a ferromagnetic material is taken through a full magnetising cycle, plotting flux density B against magnetising field H traces a closed hysteresis loop. The loop's shape is characterised by several key points, each with a distinct meaning.
The correct answer identifies remanence Br as the residual magnetic flux density that remains after the applied field H is removed. Starting from saturation and reducing H back to zero, the material does not return to B = 0; a leftover magnetisation persists because the magnetic domains stay partly aligned. That leftover value on the B-axis is the remanence, and it is what gives permanent magnets their strength.
The following comparison distinguishes the main loop parameters:
| Parameter | Meaning on the loop |
|---|---|
| Remanence Br | Value of B when H = 0 (residual flux density) |
| Coercivity Hc | Reverse H needed to bring B back to zero |
| Saturation Bsat | Maximum B the material can reach |
| Loop area | Energy lost as heat per magnetising cycle |
Why the other options are wrong:
- The maximum flux density reached in the loop describes the saturation flux density, which occurs at high H, not at H = 0.
- The applied field needed to reduce flux to zero is the definition of coercivity Hc, a field value on the H-axis, not a residual flux value.
- The area enclosed by the loop represents the hysteresis energy loss per cycle, a completely different quantity from remanence.
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