Magnets are found in everyday items and technology such as phones, computers and cars. In ambient temperatures, magnets create their own magnetic field but temperature extremes can affect the way a magnet behaves. Learn about the effect of superheating on magnets in this article.
Image Credit: Thomas Perraudin/Shutterstock.com
How Does Superheating Reduce the Magnetism of Magnets?
To understand how temperature might affect a magnet, you need to look at the atomic structure of the elements it is made of. Magnets are made of atoms and, in normal conditions, these atoms align between poles and foster magnetism. There is a delicate balance between temperature and magnetic domains – that is the atom’s inclination to ‘spin’ in a certain direction.
Temperature can either strengthen or weaken a magnet’s attractive forces. Cooling or exposing the magnet to low temperatures will enhance and strengthen its magnetic properties, while heating will weaken them.
As you heat a magnet, you supply it with more thermal energy; this allows the individual charged particles to move around at an increasingly faster and more sporadic rate. Between the weakening of overall magnetism and the availability of extra thermal energy, the spin of individual electrons within the atom – which behaves like mini-magnets – are more likely to be in high energy states.
So, heating a magnet disrupts the domain walls, making it easy for the magnetic domains, which are ordinarily lined up, to rotate and become misaligned. They are now less aligned and point in the opposite direction to their neighbors, causing a decrease in the magnetic field and loss of magnetism.
As you heat a magnet further, the individual spins within the domains become even more likely to point in opposite directions to their neighbors, decreasing their average alignment seen by their neighbors, decreasing the effect which favors their initial lining up.
At a well-defined temperature – known as the Curie temperature – the entire tendency of atoms to align into domains collapses and the material stops being a magnet. Named after Pierre Curie, the French physicist, the Curie Temperature is the temperature at which the atoms are too frantic to preserve their aligned spins. As such, no magnetic domain can exist. Even if the magnet is then cooled, once it has become demagnetized, it will not become magnetized again.
If a magnet is exposed to high temperatures, the delicate balance between temperature and the domains in a magnet is destabilized. At around 80 °C, a magnet will lose its magnetic force and it will become demagnetized permanently if exposed to this temperature for a period, or if heated above its Curie temperature. Heat the magnet even more, and it will melt and eventually vaporize.
The ease with which a magnet becomes demagnetized decreases with increased temperature. Different materials react differently under heat, so what the magnet is made of is important; different magnetic materials have different Curie temperatures, the average being between 600 to 800 °C. Magnets consisting of Alnico – an iron alloy containing aluminum, nickel and cobalt – have the best strength resistance, then SmCo (Samarian cobalt) and NdFeB (neodymium-iron-boron), followed by ceramics.
Neodymium (NdFeB) magnets have the highest resistance to demagnetization but the largest change with temperature. To elaborate, NdFeB magnetics lose some of their performance for every degree of rise in temperature. Up to 150 °C neodymium magnets are considered to have the best magnetic performance of all permanent magnetic materials.
Samarium cobalt magnets are not as strong as neodymium magnets at room temperature but have better resistance to demagnetization than neodymium magnets.
Alnico magnets are second only to neodymium magnets in terms of magnetic strength but are significantly more susceptible to demagnetization by external magnetic fields and physical shock, although not by elevated temperature.
The shape of a magnet can also affect its maximum useable temperature as the length of the magnetized axis increases, and resistance to demagnetization also increases. Small, thin magnets are generally more susceptible than magnets greater in volume to rising temperatures.
Why Is It Important to Know the Effect of Superheating on Magnets?
Given that magnets lose their strength and magnetism from superheating, it is preferable to work with magnets at ambient temperatures or in cold temperatures. Some applications of magnets, however, require them to be used in extreme heat.
Fortunately, different types of magnets cope differently in high temperatures. Understanding which magnet is correct for applications that require performance in the heat is essential. Alcino magnets, for example, cope very well in high temperatures. They are commonly used in electric motors, guitar pickups, microphones, loudspeakers, sensors, and other equipment that needs to cope with superheating to function in high temperatures. Alcino magnets have a maximum operating temperature of roughly 535 °C, much higher than a regular magnet. Its Curie temperature is 800 °C.
Rare earth magnets also cope well with superheating and have generally begun to replace alcino magnets in many of their applications. They are often used in mobile phones, disc drives, video and audio systems. The most common type of rare earth magnet is the neodymium magnet, as mentioned above. This type of magnet is often used in filters and ionizers, as well as security systems.
Ceramic magnets are another type of magnet that works well under superheating. Ceramic ferrite magnets can continue working up to temperatures of 250 °C. While they are not as powerful as rare earth magnets, they are corrosion-resistant and relatively cheap. These magnets are commonly used in refrigerators, automobiles, microphones, and cordless appliances.
Developing Magnets That Are Resistant to Superheating
Scientists have recently been experimenting with different types of alloys and composites to create stronger magnets resistant to superheating.
Additionally, scientists have been using the magnetization processes of annealing and quenching to strengthen the magnetization of a magnet, which can reduce the impact of temperature on the magnet and improve its performance under superheating conditions.
Finally, recent advances in nanotechnology allow for the engineering of the atomic and crystalline structure of magnets to boost their stability under superheating. In the future, we can expect more developments from nanotechnology that will help improve the thermal properties of magnets so that they can be used at higher temperatures.
References and Further Reading
Ask the Van; heating magnets [online]. University of Illinois. Available at: https://van.physics.illinois.edu/qa/listing.php?id=2744&t=heating-magnet
How does temperature affect magnetism? [online]. HSI Sensing. Available at: https://hsisensing.com/temperature-affect-magnetism/
How does heat affect magnets? [online]. Sciencing. Available at: https://sciencing.com/heat-affect-magnets-4926450.html
Temperature effects on permanent magnets [online]. Magnet Expert. Available at: https://www.magnetexpert.com/technical-advice-for-every-application-magnet-expert-i685/temperature-effects-on-magnets-i683
Yüksel, C. (2017) ‘The use of neodymium magnets in healthcare and their effects on health’, Northern Clinics of Istanbul[Preprint]. doi:10.14744/nci.2017.00483.
This article was updated August 2023.
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.