While going through some articles regarding our Iron, which accounts for over 90% of worldwide metal production, a question about its magnetism struck my mind. So quickly I tried to search for the answer. But even though the exact answer was clear, the reason for the same just blew my mind. So let’s look closely through this lustrous greyish metal and know something more about its hidden secrets!
So, is Iron magnetic? Iron is ferromagnetic in nature (below the curie point of 770℃, i.e in ɑ form). The main reason for this is its unpaired electrons i.e 4 unpaired electrons as we get to know from its electronic configuration. Another important reason for the strong magnetic property of Iron is the alignment of all 4 unpaired electrons or ‘spins’ parallelly, in presence of a magnetic field, ensuring enough ability to interact with the external magnetic field and move the entire object.
Iron belongs to group 8, with atomic number 26 and atomic mass 55.845 u. It is one of the most ancient elements that was used extensively for different purposes.
In the German campaign of 1813, Frederick William III commissioned the first Iron Cross as military decoration. In its metallic form, this metal is rare in the Earth’s crust.
Why is Iron Magnetic?
The magnetic property of iron largely depends on its electronic configuration, [Ar] 3d6 4s2, with 4 unpaired electrons. Parallel alignment of the 4 unpaired electrons is another important reason for its magnetism.
And in addition to that, the crystal structure of Iron also plays a role in its magnetic property. The austenitic form of iron is paramagnetic and not ferromagnetic.
A piece of iron can be magnetized in the presence of a magnetic field. When a magnet is rubbed with an iron, the north-seeking poles of the atoms in the iron line up in the same direction.
This force generated by the parallelly aligned atoms creates a magnetic field making the piece of iron a magnet. But unlike other metals, iron maintains its magnetic characteristics even if the field is removed.
If we go deeper, we can see that every material is made up of magnetic domains, which are tiny pockets containing magnetic dipoles.
When a magnetic field is introduced, these domains align themselves in a single direction and remain aligned even after the field is removed.
This tendency of “remembering the magnetic history” is called hysteresis. A magnetic field of about 1T can be produced in annealed iron with an external field of about 0.0002T.
The reason for iron’s strong magnetic field also depends on magnetic susceptibility. It is the degree to which a material can be magnetized in an external magnetic field.
This increases with increasing temperature due to the parallel alignment of dipoles towards the direction of the field.
But unfortunately, things change after Curie’s temperature. Iron loses its magnetic property at the curie point.
Thermal agitation above curie temperature is sufficiently high to destroy the alignment and change the ferromagnet to paramagnet, without any change in the crystal structure.
Is Cast Iron Magnetic?
Cast iron is basically liquid iron that has been cast.
Now the question becomes is molten/liquid iron magnetic?
Molten iron is hot enough that the atoms cannot align their magnetic fields. Thus they are neither attracted nor repelled by a magnetic field.
The melting point of iron is 1538℃ and its curie temperature is 770℃, so we can say that iron loses its ferromagnetism way before its melting point.
Along with that, the high temperature required for melting iron doesn’t let the magnetic dipoles be aligned parallelly in the direction of the magnetic field.
So molten iron can’t be ‘magnetized’, but it does have conduction powers! It is an electrical conductor, so a changing magnetic field would introduce an electric current in molten iron.
Magnetization curves of 9 ferromagnetic materials
Many other questions regarding iron’s magnetism may rise, like, is iron sulfide magnetic? The answer to this is NO.
The constituents of this compound are different from that of iron, i.e in simple words, magnetic iron in combination with sulfur loses its magnetic property and becomes non-magnetic.
Why is iron attracted to either pole of a magnet?
All the magnetic dipoles inside magnetic domains are in a haphazard manner in an unmagnetized piece of iron.
When either pole of a magnet is brought near it, the dipoles align parallelly in the direction of the magnetic field. Thus iron is attracted to either pole of a magnet.
Iron can be used to manufacture steel, used in reinforced concrete and girders. For its malleable nature, it is used in building cars. This metal also has some biological use as well.
Are complexes of iron magnetic?
The magnetic moment in iron-containing complexes largely depends on the nature of ligands.
According to the spectrochemical series, if the ligand is a strong field, then there is a possibility that the unpaired electrons can pair up, lowering the magnetic moment.
But if the ligand is a weak field, the magnetic moment will be high with unpaired electrons.
Basically, in presence of a strong field ligand, the splitting between eg (dx2-dy2 and dz2) and t2g (dxy, dyz, dxz) is high.
Thus the distance between them, denoted by Δo, is more than pairing energy. So naturally, electrons will try to be placed in the ground t2g level in paired form.
Whereas in the case of weak field ligand, this splitting is low.
Thus Δo is less than pairing energy.
So, more energy will be needed to pair up the unpaired electrons than to place them in the higher eg orbital.
Naturally, after filling up the ground t2g orbital, electrons go to eg orbital instead of pairing. The picture is given below clearly explains the above-mentioned fact.
(Here A is in the case of the complex with strong field ligand and B is in the case of weak field ligand)
Now talking in the case of iron, it prefers to be in a +3 state.
That means Fe+3 has 5 d electrons. These 5 electrons will be in unpaired fashion, in the case of [FeF6]3- but for [Fe(CN)6]3- there will be only one unpaired electron.
The reason is that fluorine is a weak field ligand compared to CN. Thus the arrangement of electrons in both cases will be;
As a result magnetic moment for [FeF6]3- is 6 B.M whereas for the other one it’s 2.3 B.M, which is quite low.
Properties of Iron
- The iron (Fe) exists as a solid at room temperature.
- It is lustrous, malleable, and ductile in nature.
- The melting point of iron is around 1538°C or 2800°F and its boiling point is 2861°C, 5182°F.
- It is a good conductor of heat and electricity.
- It attracts magnets strongly because of its ferromagnetic behavior as explained above.
So considering all the points and explanations we came to the conclusion that Iron is a ferromagnetic metal up to a certain temperature, with a very strong magnetic field because of the parallel alignment of its magnetic dipoles. It can hold its magnetic property even after the removal of the magnetic field.