A magnetic hysteresis, otherwise known as a hysteresis loop, is a representation of the magnetizing force (H) versus the magnetic flux density (B) of a ferromagnetic material. The curvature of the hysteresis is characteristic of the type of material being observed and can vary in size and shape (i.e. narrow or wide). The loop can be generated by using a Hall Effect sensor to measure the amount of magnetic field at various points - when in the presence of a magnetic field, when it is removed from the magnetic field, and when a force is applied to bring the magnetic flux back to zero. These loops are important in the memory capacity of devices for audio recording or magnetic storage of data on computer disks.
Hysteresis Loop Structure
Variations of Hysteresis Loops
|Fe||1.75 x 106|
|Co||1.45 x 106|
|Ni||0.51 x 106|
Importance of Hysteresis Loops
Hysteresis loops are important in the construction of several electrical devices that are subject to rapid magnetism reversals or require memory storage. Soft magnetic materials (i.e. those with smaller and narrower hysteresis areas) and their rapid magnetism reversals are useful in electrical machinery that require minimal energy dissipation. Transformers and cores found in electric motors benefit from these types of materials as there is less energy wasted in the form of heat. Hard magnetic materials (i.e. loops with larger areas) have much higher retentivity and coercivity. This results in higher remnant magnetization useful in permanent magnets where demagnetization is difficult to achieve. Hard magnetic materials are also useful in memory devices such as audio recording, computer disk drives, and credit cards. The high coercivity found in these materials ensure that memory is not easily erased.
1. Label the following hysteresis loop.
2. What are 3 ways to demagnetize a ferromagnetic material?
3. Which of these elements (Fe, Co, Cr, Ni) will not create a hysteresis loop? Why?
1. a) Saturation point - Hs
b) Retentivity point - Br
c) Coercivity point - Hc
2. Hit the ferromagnetic material against a surface to disorient the magnetic dipole moments, reverse the direction of the hysteresis loop, heat the material above its critical temperature.
3. Cr will not create a hysteresis loop because it is antiferromagnetic. Fe, Co, and Ni are each ferromagnetic and will therefore create a hysteresis loop.
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- Ralls, Kenneth M., Thomas H. Courtney, and John Wulff. Introducton to Materials Science and Engineering. New York: Wiley, 1976. Print.
- Bertotti, Giorgo. Hysteresis in Magnetism: For Physicists, Materials Scientists, and Engineers. San Diego: Academic, 1998. Print.
Contributors and Attributions
- Samantha Dris (B.S. Materials Science and Engineering, University of California, Davis | June 2016)