I believe that iron, nickel, and cobalt are all 3d ferromagnets. As I understood, those 3 are the only ferromagnetic elements, so why do we specify 3d? Here is an example of a 4f ferromagnet: https://doi.org/10.1016/j.intermet.2015.10.020 It seems to me that it's likely that the classification is based on which orbital the electrons contributing most to the ferromagnetic behavior, but I'm not very sure about this and it's been difficult trying to find results with a search engine since 3d is taken to mean 3 Dimensional. Any sources about how this classification is done would be greatly appreciated.

Edit: I've now found an example of a 4d ferromagnet https://doi.org/10.1063/1.361618

  • $\begingroup$ 3d is indeed an electron orbital, as is 4f. $\endgroup$
    – DKNguyen
    Apr 19, 2021 at 19:41
  • $\begingroup$ I've looked around further, and it appears that at least Nickel is somewhere between 3d10 4s0 and 3d9 4s1. To my question, why is it a 3d ferromagnet and not a 4s? $\endgroup$
    – Liam Clink
    Apr 19, 2021 at 21:00
  • $\begingroup$ Also @DKNguyen, these are molecular orbital terms. The naming of molecular orbitals tends to be based on what ionic orbitals contribute to the state more it seems $\endgroup$
    – Liam Clink
    Apr 19, 2021 at 21:08
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    $\begingroup$ Fe, Ni, Co are not the only ferromagnetic elements - it's just that they (and Gd, depending on where you draw the line) are the elements that are still ferromagnetic at room temperature. Several other rare-earth metals have lower Curie temperatures. $\endgroup$
    – Anyon
    Apr 19, 2021 at 23:35
  • $\begingroup$ That is true @Anyon, but it is still not clear to me how you decide to classify them. What class does Gd belong to? And the magnetic character typically depends on crystal structure. What about non-elemental ferromagnets like the ones I gave links to papers about? $\endgroup$
    – Liam Clink
    Apr 20, 2021 at 3:19

1 Answer 1


These aren't really classes of materials — just descriptions of which atomic orbitals are involved in the magnetic properties. These are typically determined mainly by open electron shells. Consider the electron configuration in iron: 1s$^2$2s$^2$2p$^6$3s$^2$3p$^6$3d$^6$4s$^2$ = [Ar] 3d$^6$ 4s$^2$. Note that all shells, except for 3d, are filled. Filled shells have zero net total angular momentum $\mathbf{J}=\mathbf{L}+\mathbf{S}$, and do not produce a net magnetic moment. If we're interested in understanding the magnetic properties of iron, we can, to good approximation, focus on electrons in the open 3d shell and label the system accordingly. This is why iron, nickel and cobalt are called 3d ferromagnets. For some non-elemental systems like SrRuO$_3$ you need to check the electron configurations of the ions present in the system. In this case, I think it's the Ru ions contributing 4d orbitals that cause the magnetism.

Note that this kind of shorthand isn't unique to ferromagnets — c.f. "3d block", "4d transition metal oxides", "3d-4f complexes" etc. It is useful because often systems share some properties if their electron configurations are similar - essentially the same reason that the periodic table is a useful construction.

  • $\begingroup$ Thank you for taking the time to write out a full answer. $\endgroup$
    – Liam Clink
    Apr 22, 2021 at 4:19

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