Paramagnetic vs Diamagnetic vs Ferromagnetic – Magnetism

Diamagnetic, paramagnetic, and ferromagnetic are the three main types of magnetic materials. The terms describe diamagnetism, paramagnetism, and ferromagnetism. The different types of magnetism refer to the way a material reacts to an external magnetic field. Here is a look at these three types of magnetism, examples of each, and how to tell them apart.

Factors That Affect the Type of Magnetism

Multiple factors determine whether a material is diamagnetic, paramagnetic, or ferromagnetic. But, the three main origins of magnetic properties are:

• Electron spin
• Electron motion
• Change in electron motion by an external magnetic field

Each electron carries an electrical charge. A moving electrical charge has an associated magnetic field. Electrons are always in motion, so they have magnetic fields. Most of the time, electrons occur in pairs, with one electron in a pair having opposite spin relative to the other. The magnetic fields of paired electrons cancel each other out, leaving no net magnetic field. When there are unpaired electrons, a material has a net magnetic field that causes it to react to an external magnetic field.

Diamagnetic, Paramagnetic, and Ferromagnetic Materials

Diamagnetism, paramagnetism, and ferromagnetism are the three main types of magnetism seen in materials. Other types include antiferromagnetism, ferrimagnetism, superparamagnetism, and metamagnetism. But, understanding the three main types is a good introduction to the concept.

Diamagnetism

All materials display diamagnetism, which is the tendency to weakly oppose an applied magnetic field or repel a magnet. However, not all materials are diamagnetic because other processes can overcome diamagnetism. There are no unpaired electrons in a diamagnetic material. Diamagnetic materials do not retain magnetic properties when the external magnetic field is removed. In other words, there is no permanent magnetic effect. Because they repel a magnetic field, diamagnetic substances levitate over a magnetic field.

If the electrons in a pair cancel each other out, you may wonder why a diamagnetic material repels a magnet, rather than being unaffected by it. The answer is that the magnet exerts influence on the electrons. An external magnetic field increases the orbital magnetic moments aligned opposite of the field and decreases the orbital magnetic moments that are aligned parallel to the field The overall effect is a small magnetic moment that has an opposite direction to the applied field.

Most elements on the periodic table are diamagnetic, including metals and nonmetals. Examples of diamagnetic materials include hydrogen, helium, carbon, copper, silver, and gold. Also, any conductor becomes strongly diamagnetic in the presence of a changing magnetic field because the current loops oppose the magnetic field lines. Also, a superconductor has no resistance to forming current loops, making it a perfect diamagnetic material.

Paramagnetism

There are unpaired electrons in paramagnetic and ferromagnetic materials, so the stronger effects of unpaired electrons overcome diamagnetism.

Paramagnetic materials are weakly attracted to magnets due to the unpaired electrons and change in the alignment of the electron paths from the action of external magnetic field. The electron orbits form current loops that don’t cancel each other out, so they contribute a magnetic moment. The strength of paramagnetism is proportional to the strength of the external magnetic field. The magnetic attraction is not permanent. Paramagnetic materials lose their magnetic properties when the magnet is removed.

Examples of paramagnetic materials include lithium, oxygen, sodium, magnesium, molybdenum, aluminum, platinum, and uranium.

Ferromagnetism

Ferromagnetic materials are strongly attracted to an external magnetic field, plus they retain magnetic properties after removal of a magnet. Unpaired electrons give the atoms a net magnetic moment but the attraction is strong because of magnetic domains. When unmagnetized, the domains are randomly orients, but an external magnetic field makes many magnetic moments align parallel to each other.

Examples of ferromagnetic materials include iron, nickel, and cobalt. Their alloys are also ferromagnetic, including steel.

Magnetic and Non-Magnetic Metals

Diamagnetic and paramagnetic metals are essentially non-magnetic. Ferromagnetic metals are magnetic.

Paramagnetic vs Diamagnetic – How to Tell Them Apart

If you examine the electron configuration of an element, you can predict whether it is paramagnetic or diamagnetic. In a diamagnetic atom, all of the electron subshells are complete with spin-paired electrons. In a paramagnetic atom, subshells are incompletely filled with electrons.

For example, here are the electron configurations for beryllium (diamagnetic) and lithium (paramagnetic):

• Be: 1s²2s² subshell is filled
• Li: 1s²2s¹ subshell is not filled

The same principle applies to compounds. A compound that has unpaired electrons is paramagnetic, while one with no unpaired electrons is diamagnetic. Ammonia (NH₃) is an example of a diamagnetic compound. The coordination complex [Fe(edta)₃)]^2- is an example of a paramagnetic compound.

References

• Boozer, Allen H. (2006). “Perturbation to the magnetic field strength”. Physics of Plasmas. 13 (4): 044501. doi:10.1063/1.2192511
• Du Trémolet de Lacheisserie, Étienne; Gignoux, Damien; Schlenker, Michel (2005). Magnetism: Fundamentals. Springer. ISBN 978-0-387-22967-6.
• Griffiths, David J. (1998). Introduction to Electrodynamics (3rd ed.). Prentice Hall. ISBN 978-0-13-805326-0.
• Jiles, David (2015). Introduction to Magnetism and Magnetic Materials (3rd ed.). Boca Raton: CRC Press. ISBN 978-1-4822-3887-7.
• Tipler, Paul (2004). Physics for Scientists and Engineers: Electricity, Magnetism, Light, and Elementary Modern Physics (5th ed.). W.H. Freeman. ISBN 978-0-7167-0810-0.