# Magnetic domains, hysteresis, and hard/soft magnets

Magnetic domains, hysteresis, and hard/soft magnets

05/22/17

“How do magnetic fields come about and how can we apply this knowledge?”

The subatomic interactions in a magnetic object from material properties give rise to its macroscopic phenomena. Magnetic materials are composed of divisions known as magnetic domains that have a random magnetic field direction. When an external magnetic field is applied to a material, all of these domains will align with said field and produce a magnetic force. The magnitude of this magnetic force emanating from the object will be the result of the summation of the magnetic fields from all of the individual domains.

This theory can be applied using a hysteresis loop operates as follows. Take a piece of metal. Now run a coil around it. Generate an AC voltage. At t = 0, there will be magnetic activity in neither the metal nor the coil. When the voltage is increased, it will cause the domains to line up, eventually reaching a maximum value. Now pull the voltage in the other direction. When the voltage is equal to zero, the metal will have some residual magnetic field in it as a result of the shifting domains. If we pull the voltage into a negative state, then eventually it will reach another maximum (at the negative of the original boundary). If we reverse the direction of the current again to zero, then we will also have some residual magnetic field at zero. And if we increase the voltage in the positive direction, then we will reach the maximum again (Schuster, Doc).

Based upon their hysteresis profile, a material may be classified into either a hard magnet or a soft magnet. The former has a large profile, and are often used for energy intensive applications such as permanent magnets, while the latter has a smaller profile ideal for use in low energy loss application such as transformers.

Atulasimha, Jatulasimha. “Magnetism.” Magnetism for General Audience. Virginia Commonwealth University, 8 Nov. 2015. Web. 22 May 2017.

Callister, William, and David G. Rethwisch.Materials Science and Engineering: An Introduction. 9thed. , John Wiley & Sons, Inc., 2014.

Magnetic Hysteresis or I KNOW WHAT YOUR MAGNET DID LAST SUMMER | Doc Physics. Dir. Doc Schuster. Perf. Doc Schuster. Youtube. Doc Schuster, 25 Feb. 2014. Web. 22 May 2017.