The hysteresis is very common on materials and systems. It’s the capacity to keep a property, after remove the stimulus that induces this property.
Hysteresis on magnetism
The motion of electric charges produces a magnetic field. Therefore, the movement of electrons around the atom’s nucleus generates a magnetic field.
Due to crystalline structure, a ferromagnetic material is divided in many magnetic domains, these are regions where atoms are oriented in a direction.
When a ferromagnetic material is submitted to a magnetic field, material’s atoms are aligned with the external magnetic field. Consequently, the material becomes magnetized, with north and south poles.
When all magnetic domains are pointed to direction of external magnetic field, the material reaches the saturation. By that, increasing magnetic flux intensity H, won’t increase flux density B. After the removal of external magnetic field, most of domains keep pointed to same direction and the material keeps magnetized.
Each material has a unique hysteresis loop. The equation below is the relation between magnetic field and flux density.
B=\mu H
Where \mu is magnetic permeability, which depends on material.
Some hysteresis examples in other areas
Electronics
The comparator electronic circuit called Schmitt-Trigger, has the function to change the output digital signal (V_{OUT}) from “LOW” level to “HIGH”, when input voltage (V_{IN}) increases to a determined value (V_{TH}). If output signal is on “HIGH” level, it will go to “LOW” level, when input voltage reaches a determined value (V_{TL}).
Elastic materials
When an elastic material receives an external force, the material can return to its original shape if the force stops. However, if the force is high enough, the material deforms and don’t totally recover its original shape.
