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To know if an element is paramagnetic or diamagnetic, it is necessary to understand how these behaviors occur and what they are. To start with, you should know that all materials experience some kind of reaction to magnetic fields. That is, all materials have a magnetic moment. The magnetic moment measures the strength and direction of an element’s magnetism. Thus, it is a vector quantity, that is, with magnitude and direction. On the other hand, magnetism is the force generated by magnets when they attract or repel each other.
Now, all substance is made up of small units called atoms. Atoms contain electrons, which are electrically charged particles. Electrons spin like tops around the nucleus of the atom. The electrical current generated by this movement causes each electron to act like a small magnet. Thus, it is the electrons that give rise to the magnetic properties of matter.
The magnetism of a substance can be nullified, since most of these have an equal number of electrons that spin in opposite directions. However, for there to be magnetism another strong substance must enter the magnetic field of an existing magnet.
All magnets have two poles: north pole and south pole. As is known, opposite poles attract and identical poles repel. When a piece of iron is rubbed across a magnet, the north-facing poles of the iron atoms align in the same direction. The force generated by the aligned atoms generates a magnetic field. Here, the piece of iron has become a magnet.
Said magnetic force has different behaviors, among them is paramagnetism, diamagnetism and ferromagnetism.
What is diamagnetism?
This type of magnetism is characteristic of materials that align at right angles to a non-uniform magnetic field. Likewise, the diamagnetic elements partially expel from their interior the magnetic field in which they are found. Diamagnetism was first observed in 1778 by SJ Brugmans, but it was named and studied from 1845 by Michael Faraday. This and other scientists discovered that most compounds, as well as some elements, exhibit this type of magnetism, which they called “negative” magnetism.
This is because diamagnetic materials do not have a net magnetic moment. Therefore, they must have the presence of an applied magnetic field (H). However, when an external magnetic field is applied to a diamagnetic material, the spinning electrons experience motion. This movement, which produces an electric current, is known as processing and, as a result, gives rise to a magnetization (M), in the opposite direction to that of the external magnetic field. Therefore, diamagnetic materials have a small negative magnetic susceptibility (χ) and a slightly higher permeability than vacuum (μ0). However, the susceptibility value is independent of temperature, which does not affect diamagnetism.
Diamagnetism in solid materials is also explained by Lenz’s Law. In this it is stated that an induced current accelerates or slows down the electrons that orbit the atoms, so that they oppose the action of the external field. That is, diamagnetic atoms are not attracted by a magnetic field, but repelled.
paramagnetism and ferromagnetism
On the one hand, paramagnetism refers to the magnetic state of an atom that has one or more unpaired electrons. Unpaired electrons are attracted by a magnetic field. This is due to the magnetic dipole moments (force of attraction between two atoms) of the electrons. Hund’s rule states that electrons must occupy all orbitals individually before any orbital is occupied twice. When the orbitals are properly filled, the atoms are left with unpaired electrons moving in any direction. Thus, magnetic moments also act in any direction, allowing paramagnetic atoms to be attracted by magnetic fields.
On the other hand, when an electron is alone in an orbital, the orbital has a net spin. This is because the spin of the lone electron does not cancel. Therefore, an atom is considered to be paramagnetic when it contains at least one paramagnetic electron. In simple words, an atom can have ten paired (diamagnetic) electrons and one unpaired (paramagnetic) electron. Such an atom would still be considered a paramagnetic atom.
Let us now see what ferromagnetism consists of. When the magnetic moments of all the atoms in a material’s lattice are parallel to each other, they are known as ferromagnetic. This is because the magnetic domains of the material are aligned in only one direction. The domains of the material determine its magnetization with the application of the magnetic field. Contrary to diamagnetism, the alignments of magnetic moments in ferromagnetic material decrease with temperature. Likewise, the susceptibility of ferromagnetic materials is high.
Just as diamagnetic atoms are slightly repelled by a magnetic field, paramagnetic atoms are slightly attracted by a magnetic field.
How to know if a substance is paramagnetic or diamagnetic
As we are going to see now, to determine the magnetic properties of a substance, it is enough to examine its electronic configuration. So:
- If it has unpaired electrons, the substance is paramagnetic.
- If all the electrons in a substance are paired, that substance is diamagnetic.
This verification process can be done in three steps:
- Write down the electronic configuration of the substance.
- Draw the valence orbitals.
- Identify whether the substance has unpaired electrons.
With these steps, you will be able to determine what kind of magnetic behavior a substance has.
Examples of diamagnetic elements
- Bismuth.
- Mercury.
- Silver.
- Carbon.
- Lead.
- Copper.
Examples of ferromagnetic elements
- Iron.
- Nickel.
- Cobalt.
- Gadolinium.
- dysprosium.
Examples of paramagnetic elements
- Uranium.
- Platinum.
- Aluminum.
- Sodium.
- Oxygen.
Sources
- Magnetism in the Geographic Information System (GIS) from the National Geographic Education Resource Library.
- Magnetic Properties at LibreTexts Libraries, accessed February 15, 2021.
