By Ted Rush – Updated March 24, 2022
Boosting a magnet’s performance—whether it’s a custom‑built superconducting coil or a conventional piece of iron—often comes down to a single variable: temperature. By cooling the material, scientists can lower its electrical resistance, increase the flow of electrons, and generate a stronger magnetic field. This principle underpins everything from high‑field research laboratories to the MRI scanners that diagnose patients worldwide.
The quantity that governs a moving charge is called electric current. When electrons flow through a conductor, they create a magnetic field. The strength of that field scales with the magnitude of the current. In permanent magnets, the electron motion is confined to the atoms themselves, whereas in electromagnets it is the electrons that traverse the wire windings.
Current can be raised by increasing the number of charge carriers or by speeding them up. The elementary charge of an electron is immutable, so the practical route is to reduce the resistance that hinders its motion. Lower resistance means electrons can accelerate more easily for a given voltage, raising the current and, consequently, the magnetic field.
Electrical resistance measures how strongly a material opposes the flow of electrons. Copper is prized for its low resistance, while wood is a poor conductor because its resistance is high. The most straightforward way to alter a material’s resistance is to adjust its temperature.
Resistance varies predictably with temperature: cooler temperatures produce lower resistance. By cooling conductive components, engineers can boost current without adding extra power, thereby enhancing the magnetic field. This temperature dependence is a cornerstone of modern magnet technology.
Some materials exhibit a dramatic drop in resistance when they reach a critical temperature—so dramatic that the resistance approaches zero. These superconductors allow current to flow with negligible energy loss, producing exceptionally strong magnetic fields. According to the textbook Physics for Scientists and Engineers, there are thousands of known superconducting compounds. The High Magnetic Field Laboratory at Radboud University in Nijmegen, Netherlands, harnesses this effect to power a magnet so intense that even a frog, which is normally non‑magnetic, can be levitated above its coils.
