# I Susceptibility of Ferromagnetic materials

1. Dec 22, 2017

A complete table of the ac susceptibility $\chi_m$ of various ferromagnetic materials, where $M=\chi_m H$, is something that I have had trouble finding in a google of ferromagnetic materials. In what I have been able to come up with to date, there is quite a spread in the values of susceptibility for ferromagnetic materials, presumably because the applied $H$ can be quite small and the magnetic state that occurs in these ac type materials is close to that of a permanent magnet, where $H$ can be zero and the magnetization $M$ persists. $\\$ One article that I was able to google contained a very incomplete table. http://electrons.wikidot.com/ferromagnetic-materials. I would welcome any similar articles that describe the differences in materials that determines whether a given material results in a permanent magnet, or whether a material has a high ac susceptibility, but returns to near zero magnetization upon removal of the applied field $H$.

2. Dec 22, 2017

### Nidum

Try searching for manufacturers and , separately , using metallurgical/chemical or trade names for alloys .

Just for example :

Cobalt Iron

3. Dec 22, 2017

That would be one way that might be helpful. It would appear the available literature is somewhat lacking in this area if that is the quickest way to find information on the various ferromagnetic materials.

4. Dec 22, 2017

### Nidum

5. Dec 22, 2017

I got similar types of displays with a google. Most of the articles were very specialized. What I'm looking for is a compilation of many different materials. $\\$ Editing: I just tried something different: I googled it as "permeability" rather than "susceptibility" and I'm getting better results. One result that was reasonably good is the following: http://chemical-biological.tpub.com/TM-1-1500-335-23/css/TM-1-1500-335-23_239.htm One item of interest is the tremendous variation in the numbers for $\mu_r$, ranging from 100 to 200,000.

Last edited: Dec 22, 2017
6. Dec 22, 2017

### Nidum

7. Dec 22, 2017

8. Dec 22, 2017

One additional comment: In looking at the extremely high magnetic permeability values, (post 5), it is really rather remarkable that many materials return to a non-magnetized state, instead of staying in a state of permanent DC magnetization (permanent magnet state) upon removal of the applied field $H$ for these materials. Apparently, there is a non permanent magnet state that is energetically favorable or a permanent magnet would result. (The permanent magnet is an energetically favorable state for permanent magnets). It would seem to me this state of low magnetization likely consists of many microscopic magnetic domains in somewhat random directions that are each individually permanent magnets of their own, but I have been unable to find any good write-up of this in the literature. If anyone has a good source for a paper that would answer this question of why a material with such a high permeability so often does not result in a permanent magnet, it would be welcomed. :)

Last edited: Dec 22, 2017
9. Dec 22, 2017

### cairoliu

Permeability has nothing to do with a "frozen magnetic state". Only the magnetic hysteresis graph just tells you the possibility.

10. Dec 22, 2017

The complete energetics of it gets complicated by the exchange effect, but when a magnetic moment $\mu$ inside a uniformly magnetized material has energy $E=-\mu \cdot B$ simple calculations show that the permanent magnet is energetically favored if there is sufficient magnetization $M$ per unit volume. Very elementary calculations using surface current per unit length $K_m=c M \times \hat{n}$ that give the $B$ inside the permanent magnet give this result. The possibility of individual domains is a complicating factor, along with the exchange effect, which seems to make simple calculations non-applicable here. I haven't seen any semi-elementary text treat this in detail where it could be readily understood... (Meanwhile there is an energy term from the magnetic field, energy density $U=\frac{B^2}{8 \pi}$ but if the $U=-M \cdot B$ outweighs this, it would make the permanent magnet state energetically favorable without additional complicating factors such as individual magnetic domains and the exchange effect).