# Resources for ferromagnetics

I am looking for experimental data on the experimental strength of magnetic fields inside ferromagnetic materials. Here is what I mean.

If all of the magnetic moments of the molecules are aligned in the same direction in the material will act as a bar magnet with field straight $H_0$.

Theoretically one could just compute this field by adding up all of the of magnetic fields of the individual molecules.

Various real-world considerations makes me feel as this isn't likely to be too accurate of a measurement. Is there a resource with experimental results for the strength of $H_0$ for various ferromagnetic materials?

Edit: To add to Phil's post below this can be computed from knowing the experimental saturation permeability $\mu_{sat}$ and the field strength at which it occurred $H_{sat}$.

• Physical layout matters. And the real worls odds pof getting a uniform field are small - BUT the variation may be insignificant. BUT there are various computer programs available that do a very good job of producing answers close to reality - often by finite element modelling to effectively "add up all the fields" as you suggest. Rushing - but use a few terms like em field simulation and modelling and FEM etc and a serach engine will return some good material.. Commented Feb 21, 2014 at 19:39

Is there a resource with experimental results?

Yes, the permeability figure from the material's datasheet. If $\mathbf{H}$ is the uniform field in which you place the material, and $\mathbf{B}$ is the field that results from that field plus the magnetic alignment of the ferromagnetic object, then permeability $\mu$ is defined by:

$$\mathbf{B}=\mu \mathbf{H}$$

For real ferromagnetic materials, permeability can be a function of field strength, frequency, temperature, and other variables. The datasheet will elaborate on the more significant variables.

After discussion, it seems you may be wondering what the maximum contribution to the magnetic field a ferromagnetic material could make, if all its magnetic domains were aligned. That is, when all the magnetic domains are aligned, what would the magnetic field of the material be?

When this happens, the material is said to be saturated. You will find this information in the datasheet as well. It is usually specified as the auxiliary field strength ($\mathbf{H}$ from above) which is sufficient to fully align all the magnetic domains in the material. Above this field strength, $\mu$ effectively drops, since the material can't become any more magnetized.

• This is what I had thought but something posted on physics forums / physic SE had me confused about the issue. I seem to be having no luck in locating it. Commented Feb 21, 2014 at 19:21
• @MathEE locating what? The datasheet? Or you have the datasheet, and can't find permeability on it? Commented Feb 21, 2014 at 19:25
• The thread on physics forums or physics SE that I read a few weeks back. Commented Feb 21, 2014 at 19:27
• @MathEE see edits. Commented Feb 21, 2014 at 20:05

Are there resources for computing the magnetic field strengths of ferromagnetics?

"Magnetic field Strength" (H) is defined in units of ampere-turns per metre. See this page for additional information. Basically, H has nothing to do with the ferrite material itself but rather the number turns that carry a certain current that in turn leads to a distribution of a magnetic field in a particular physical path. How it applies to ferrites (or other materials with permeabilities greater than air or a vacuum) is that the magnetic field is largely contained within the ferrite and this makes it easier to calculate the "per metre" part of H. Obviously amps and turns are dead easy to figure.

Ferrites themselves cannot be classed as having a magnetic field strength - they actually are fed with it and in turn this produces a certain flux density inside the ferrite, B. The larger the permeability of the ferrite material, the greater the flux density, B.

The rest of your question appears to be based on a premise that H is something else. I would also point out that a magnetic field isn't "induced" just like a current isn't induced in a resistor when a voltage is applied. This might be going down the path of semantics but, in terms of magnetics, the word "induce" is usually reserved for voltage being induced in a coil by a changing magnetic field. Not a biggy but thought I'd mention that.

• Yes, thank you for pointing it out. I meant it as informal English instead of something more scientific. Commented Feb 21, 2014 at 19:20