| MadSci Network: Physics |
Steel is ferromagnetic material, which is composed of large amount of magnetic domains. Each magnetic domain is like a tiny magnet. Normally these tiny magnets are randomly oriented, therefore steel does not show magnetic force. When we move a permanent magnet close to a steel sheet, the magnetic field of the permanent magnet causes the tiny magnets in the steel sheet to be oriented, which makes the steel sheet behave like a magnet. This process is called magnetization.
After the steel sheet is magnetized, it will have north and south poles. The north poles are locations where the magnetic force lines exit the steel sheet, whereas the south poles are locations where the magnetic force lines enter the steel sheet. Knowing the preoperty and shapes of the magnets and the steel sheet, we can calculate the magnetic field by using numerical method.
In this figure the top and bottom rectangles represent the two permanent magnets, and the middle rectangle represents the steel sheet. Here I assume the relative permeability of the steel sheet is 10000 and omit its non-linearity and hysterisis. It may not be very accurate but the result should still capture the essence of the physics involved here.
From this figure we can see that the steel sheet has south poles at the contact regions with the two magnets, which explains why the two permanent magnets are attracted to the steel sheet. The north poles of the steel sheet are scattered at other areas surrounding the contact regions.
The orientation of domains in the steel sheet should be able to be deducted based on the magnetic field in it.
References
A software for 2D magnetostatic simulation. The figure in the answer is obtained by using this software. It has a 30 day trial version. It is a very good tool for visualizing and understanding magnetic field.
[2]http://www.aacg.bham.ac.uk/magnetic_materials/
A good tutorial about magnetic material.
[3]B. G. Elmegreen, R. H. Koch, M. E. Schabes, T. Crawford, T. Ebisuzaki, H. Furusawa, T. Narumi, R. Susukita, and K. Yasuoka, Simulations of magnetic materials with MDGRAPE-2, IBM Journal of Research and Development, vol 48, no 2, 2004.
A paper on the simulation of magnetic field through a particle approach. It
may be a little difficult for non-researchers.
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