The strongest magnet involves two categories: permanent magnets, which generate a field without external power, and temporary electromagnets, which require an electrical current. The strength of any magnet is determined by its material composition and the engineering principles applied in its design. Understanding the absolute strongest magnet requires appreciating this fundamental difference between intrinsic material strength and externally powered field generation.
How Magnetic Strength is Quantified
The performance of a permanent magnet is determined by three key metrics derived from its demagnetization curve. Magnetic field strength is measured in Tesla (T) or Gauss (G), where one Tesla equals 10,000 Gauss. To compare the quality of the magnet material, scientists rely on specific indicators.
Remanence (\(B_r\)) measures the magnetic flux density that remains after an external magnetizing field is removed. Coercivity (\(H_c\)) represents the magnet’s resistance to demagnetization, indicating the strength of the reverse magnetic field required to reduce the residual magnetic flux density to zero.
The Maximum Energy Product (\((BH)_{max}\)) is the most comprehensive measure of a permanent magnet’s overall strength and efficiency. This value is calculated as the maximum product of the magnetic flux density (\(B\)) and the magnetic field strength (\(H\)) along the demagnetization curve. Expressed in MegaGauss-Oersteds (MGOe) or kilojoules per cubic meter (\(kJ/m^3\)), \((BH)_{max}\) dictates the maximum magnetic energy the material can store per unit volume, which directly correlates to the magnet’s pull force and size efficiency.
The Dominant Material: Neodymium
Within permanent magnets, the undisputed strongest commercially available material is Neodymium Iron Boron, abbreviated as NdFeB or Neo magnets. These rare-earth magnets are composed primarily of neodymium (Nd), iron (Fe), and boron (B), forming the specific tetragonal crystalline structure \(\text{Nd}_2\text{Fe}_{14}\text{B}\).
The extraordinary strength of NdFeB magnets stems from the unique properties of the neodymium atom, which possesses four unpaired electrons. This configuration allows the material to achieve an exceptionally high magnetic dipole moment, contributing to high saturation magnetization. When processed, the microcrystalline grains are aligned in a powerful external magnetic field, resulting in a high Remanence (\(B_r\)).
The \(\text{Nd}_2\text{Fe}_{14}\text{B}\) crystal structure provides the material with high resistance to demagnetization, known as high coercivity. This combination of high Remanence and high Coercivity results in the highest Maximum Energy Product values, often exceeding 50 MGOe for top-tier grades. Neodymium magnets are graded based on their \((BH)_{max}\) value, with grades like N52 representing a high energy product.
Other High-Performance Permanent Magnets
While Neodymium leads in raw magnetic strength, other permanent magnet materials offer distinct advantages in specialized environments. Samarium Cobalt (SmCo) is the second most powerful rare-earth magnet, possessing slightly lower strength than Neodymium. The primary benefit of SmCo is its superior thermal stability and corrosion resistance, retaining magnetic properties at operating temperatures that would cause Neodymium magnets to lose strength.
Alnico magnets, an alloy of aluminum, nickel, and cobalt, offer a high operating temperature tolerance, often surpassing the thermal limits of both rare-earth types. However, Alnico has lower coercivity, meaning it is more easily demagnetized by external fields compared to NdFeB or SmCo magnets.
Ferrite, also known as ceramic magnets, are composed of iron oxide and other metal oxides, making them the most cost-effective and chemically stable option. Ferrite magnets have significantly lower magnetic strength, with a maximum energy product ranging from 10 to 88 \(kJ/m^3\) (approximately 1.3 to 11 MGOe). These materials are chosen when cost, temperature stability, or resistance to corrosion are prioritized over achieving the highest magnetic force in the smallest volume.
Superconducting Electromagnets: A Different Class
When considering the absolute strongest magnetic field possible, the focus shifts entirely from permanent materials to temporary, powered electromagnets. These devices use coils of wire that generate a magnetic field only when an electric current flows through them. The most powerful version utilizes superconductivity, where the coils are cooled to cryogenic temperatures, typically using liquid helium or nitrogen.
In the superconducting state, the wire loses all electrical resistance, allowing immense current to pass through the coils without energy loss from heat. This ability to conduct larger electric currents enables superconducting electromagnets to generate magnetic fields orders of magnitude stronger than any permanent magnet. While the strongest permanent magnets might reach a residual flux density of around 1.3 Tesla, advanced superconducting magnets, constructed with materials like Niobium-Titanium or Niobium-Tin, routinely exceed 15 to 25 Tesla.
These temporary magnets are the record-holders for field strength. They are employed in applications requiring intense magnetic fields, such as Magnetic Resonance Imaging (MRI) machines, particle accelerators, and fusion reactors. The overall strongest type of magnet is a superconducting electromagnet, but the strongest permanent magnet remains the Neodymium Iron Boron alloy.