# What is the magnetic susceptibility of NdFeB?

NdFeB is one of the most popular materials used for making permanent magnets. Yet I could find no link or reference reporting a decent value for the magnetic susceptibility of NdFeB.

Magnetic susceptibilities of some common materials has been listed at the following link: http://en.wikipedia.org/wiki/Magnetic_susceptibility#Examples

A scientific paper or application notes of a good company involved in magnetism would be really helpful.

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I tried adding the tag magnetism. It's automatically being changed to electromagnetism. I wonder what bug this is. –  Shashank Sawant Dec 2 '11 at 20:24
It's not a bug. The magnetism tag is a declared synonym of electromagnetism because any questions about magnetism should be "filed" under electromagnetism. –  David Z Dec 3 '11 at 0:18
Think about why no hard/ferromagnetic materials are included in that list! –  Georg Dec 3 '11 at 1:25

Susceptibility in general is the response of an object to an external influence. The magnetic volume susceptibility is defined as:$$\chi_v = \frac{\partial\mathbf{M}}{\partial\mathbf{H}}$$ So a high susceptibility means you will get a steep response or magnetization $\mathbf{M}$ for a small applied external field $\mathbf{H}$. This definition works nicely for all paramagnetic materials. In ferromagnetic materials and especially in hard ferromagnets like NdFeB you have a large hysteresis. Without any applied field the material shows a finite magnetization and the susceptibility is not well defined (infinite). A more useful parameter to compare different ferromagnetic materials is the relative permeability.