Video Overview
Iron is the most famous magnetic material, and it gives its name to the strongest form of
magnetism: ferromagnetism (ferro is derived from ferrum , the Latin for iron). A
ferromagnetic material is strongly attracted to magnets and some can be turned into magnets
themselves.
However, you may have heard that iron is not the only element that can be magnetic; cobalt
and nickel can be as well. In fact, there is one more member of this family, but they only
show up on a cool day.
Every ferromagnet has its temperature limit, which is called its Curie temperature. If the
temperature goes above this limit, the substance loses its ferromagnetism.
Element
Iron
Cobalt
Nickel
Curie Temperature (∘ C
770
1,115
354
The only other element that can be ferromagnetic is gadolinium.
Element
Gadolinium
Curie Temperature (∘ C
20
Gadolinium has a much lower Curie temperature. Cool a piece of gadolinium with ice water, and
it will respond to a magnet strongly. Warm it up (perhaps with a heat gun), and the gadolinium
will fall away from the magnet.
Above its Curie temperature, gadolinium will respond a little to a magnet, but not a lot.
Other elements behave in a similar way, like terbium and dysprosium, but require a lot more
cooling. They are also not as strongly attracted to magnets as ferromagnetic materials; they
are said to be paramagnetic.
Element
Terbium
Dysprosium
Curie Temperature (∘ C
−
5
4
−
1
8
5
Magnetism arises because of a complex combination of the electromagnetic force and special
relativity. Moving charges and particles with a property called spin can produce a magnetic
field.
Every electron, neutron, and proton is a little magnet; however, electrons are about 10,000
times stronger magnets than neutrons and protons. When bound in an atom or ion, electrons are
even stronger magnets.
Electrons in gadolinium are mostly paired up in orbitals, canceling each other out.
However, gadolinium atoms have 8 unpaired electrons in total (1 in the 5d subshell and 7 in
the 4f subshell). These all contribute to the net magnetism of each atom (each atom is said to
have a magnetic moment).
A material, like gadolinium, can be treated like a lot of little bar magnets, where the net
effect of all the electrons in one region is treated as a single magnet.
Below its Curie temperature, gadolinium is ferromagnetic, and the magnetic moments of a
region, called a domain, are aligned. If the gadolinium is not magnetized, the magnetic
moments of the domains are randomly oriented and collectively cancel each other out.
If ferromagnetic gadolinium is exposed to a magnetic field, the magnetic moments of each
domain align.
Above its Curie temperature, gadolinium is paramagnetic. This means that all the magnetic
moments are randomly oriented.
If paramagnetic gadolinium is exposed to a magnetic field, slightly more magnetic moments
align with the field than against it.
The stronger the net magnetic moment of gadolinium, the more strongly it is attracted to a
magnet.
Temperature Range
State
Attraction to Magnet
< 2 0 ∘ C
Ferromagnetic
Strong
> 2 0 ∘ C
Weak
Paramagnetic
