I cannot find any list of para-, ferromagnetic materials by attraction strength.

Particularly, I would like to know which of these (not magnetized) metals is attracted stronger to the magnet?


The force on a magnetic moment $\vec{m}$ when in a magnetic field $\vec{B}$ is

\begin{equation} \vec{F} = \vec{\nabla}(\vec{m}\cdot\vec{B}). \end{equation}

The macroscopic magnetic moment $\vec{m}$ of an object is related to the saturation magnetization $M_s$, defined as the magnetic moment density when the material is subjected to a field strong enough to align all its moments (i.e. a saturating field). So a material with greater $M_s$ will feel a stronger force when exposed to the same field*.

From Kittel's Introduction to Solid State Physics:

\begin{array}{|c|c|} \hline \mathrm{Element} & M_s \; [\mathrm{emu}/\mathrm{cm}^3] \\ \hline \mathrm{Fe} & 1707\\ \mathrm{Co} & 1400\\ \mathrm{Ni} & 485\\ \hline \end{array}

So iron is the strongest.

*As long as the field is strong enough to align all the magnetic moments. If $|H|<H_c$, all bets are off because the exact force on the magnet depends on the macroscopic magnetic moment, which depends both on the coercivity $H_c$ of the particular magnet in question as well as the field history. Since the question was about Fe, Co, or Ni, materials which tend to have low coercivity, I'm assuming here that the field is strong enough to saturate the metal.


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