Atomic Magnets: Exploring The Magnetic Behavior Of Electrons

The electron e- is a negatively charged elementary particle. In the standard model, it is classified as a member of the lepton family. As a very simple particle, it has no inner structure and a mass of about 1/1840 the mass of the proton. The electron has been heavily described using quantum mechanical theory. One very important result is that an electron can be described by various quantum numbers. Importantly, the spin quantum number assigns unique properties to every electron in an atom

The electron is responsible for many properties of matter. They constitute the electric current, are responsible for chemical bonding and reactions, impart color to substances, conduct heat, and give rise to magnetic properties. We know from electromagnetic theory that a moving charge generates magnetic fields. Therefore, electrons as individual entities are magnets in their own right. We shall see in this article how electrons behave like magnets and how magnetic behavior arises. I have tried as much as possible to avoid the use of equations in this article yet, I discovered that I couldn’t do without putting at least a few of the very important mathematical relationships. As this is a science blog, not a scholarly website, which could be read by those with or without a scientific background, the concepts will be explained avoiding the advanced and rigorous mathematical framework used to describe the phenomenon. 

The orbit of the electron around the nucleus is similar to the orbit of the earth around the sun. Just as the earth rotates around its axis and revolves around the sun, the electron does the same. The rotation is the intrinsic angular momentum (spin) while the revolution is the orbital angular momentum. Do you know that the discovery of this spin helped to solve anomalies observed in the splitting patterns of spectra in magnetic fields, the so-called anomalous Zeeman effect?

Atoms are composed of protons, electrons and neutrons. The angular momentum of electrons make them atomic magnets

Electrons have a spin of + or - 1/2. It also has a magnetic moment along its axis of spin. This gives a very important physical constant ~ 9.27 x 10^-24 J/T. This is called the Bohr magneton. I will emphasize that this is a very important physical constant but how important do you see it? Let's see what the magnetic moment is

The magnetic moment is simply the orientation of the magnetic field of a magnet or any object capable of generating a magnetic field so this will include all magnetic substances from compass needles to elementary particles. In the presence of an external magnetic field, a torque is exerted on the field. This can also be taken as a measurement of magnetic moment. Asign on an electron’s magnetic moment indicates whether its spin is in the same direction as the magnetic field. Negative means anti-parallel. 

We can compare the orbital magnetic moment of an electron to a wire loop carrying an electrical current. Just like how a moving current generates a magnetic field, so does a moving electron. So a circular loop can be described just as an electron moving around the nucleus. Considering the electron as a body with similar mass and charge distribution and rotating around an axis, the magnetic dipole moment is:

μ=-e/2m•L

which can be derived from simple equations. The magnetic moment is related to the Bohr magneton by a simple relationship:

μ=-μ′m

A dimensionless value that gives the relationship between the observed and predicted magnetic moments is the g-factor.

Just like this bar magnet, the electron has a magnetic dipole

Why Is The Electron Spin And Magnetic Properties Important?

The spin of electrons is very important in nuclear magnetic resonance spectroscopy. This is because, just like protons, electrons are charged and can produce a magnetic field which can cause shielding of the protons in the nucleus. Shielding leads to upfield chemical shifts in the spectrum which can enable identification of the types, position, and number of protons in molecules, enabling us to determine the molecular structures of unknown compounds. This same principle is the basis of Magnetic Resonance Imaging which is a very important technique in medicine to generate pictures of internal organs in the body and to diagnose diseases.

Electron spins enable us to study substances that have unpaired electrons in their electronic structure. This includes free radicals and magnetic solids. It therefore enables the identification of radicals formed in chemical reactions. This technique is known as electron paramagnetic resonance spectroscopy.

One interesting complex phenomenon is the spin-orbit coupling. This is the complex interaction between a particle's spin and orbital motion in an electromagnetic field. One important result of this interaction is the splitting of energy levels in atoms known as the fine structure. This phenomenon is very important in studies of spin relaxation, anisotropic magnetoresistance, and magnetic anisotropy. The effect is also central to the field of spintronics providing wide prospects and technological applications and plays a key role in the workings of atomic clocks.

These are tracks of subatomic particles in bubble chamber. Since muons for example have an electric charge, they can be described using similar quantum mechanical equations for electrons

Electron magnetism is very important to physics and chemistry. It is essential for our understanding of chemicals and other interesting materials such as semiconductors and magnetic compounds. It forms the basis of quantum mechanics for a description of other subatomic particles and their interactions and in the future, could be used to create smart electronics for computers and robotics.