By Karen G. Blaettler
Updated March 24, 2022
Magnetism is a subtle yet powerful phenomenon that powers everything from compasses to modern electronics. Understanding the materials that create magnetic fields helps demystify the invisible forces that attract and repel objects around us.
A magnet is any object that generates a magnetic field and can interact with other magnetic fields. Every magnet has two poles—north (positive) and south (negative)—and the field lines travel from the north pole to the south pole. Opposite poles attract, while like poles repel.
Permanent magnets can be classified by the materials they contain. The most common include:
Natural lodestone, magnetite is the weakest permanent magnet yet the first used for navigation. Its magnetic strength is modest, but it played a pivotal role in early compass development.
Developed in the 1930s, Alnico is composed of roughly 35% aluminum, 35% nickel, 15% cobalt, with trace amounts of copper, titanium, and additional aluminum. Alnico magnets excel in high-temperature environments (up to 540 °C) and resist corrosion, making them ideal for audio equipment and industrial applications. However, they are less powerful than modern rare‑earth magnets and can demagnetize if exposed to strong external fields.
Ferrite magnets combine iron oxide with either barium oxide (BaO·6Fe2O3) or strontium oxide (SrO·6Fe2O3). They are inexpensive, corrosion‑resistant, and highly resistant to demagnetization, but their brittleness limits some applications.
First introduced in 1967, these rare‑earth magnets feature a base composition of SmCo5 and, since 1976, an alloy Sm2(Co,Fe,Cu,Zr)17. They maintain performance at temperatures up to ~500 °C and remain stable in humid conditions, yet their high cost and brittleness restrict widespread use.
Invented in 1983, NdFeB magnets contain about 70% iron, 5% boron, and 25% neodymium. They are the strongest commercially available permanent magnets, offering exceptional power‑to‑weight ratios (up to 1,300 ×). Because of their low Curie temperature (~350 °C) and susceptibility to corrosion, they are typically plated with nickel, aluminum, zinc, or epoxy.
Soft iron materials—such as nails and paper clips—become magnetized when placed in a magnetic field. The alignment of atomic magnetic moments is temporary; once removed from the field or subjected to heat, shock, or time, the magnetism dissipates. In some cases, strong enough exposure can even induce permanent magnetization.
When electric current flows through a wire coil, the resulting magnetic field is enhanced by a soft‑iron core. Increasing current strength boosts the field; cutting the current turns the magnet off instantly. Electromagnets are indispensable in applications ranging from MRI machines to industrial lifting magnets.
The planet’s magnetic field originates from a dynamo effect: a rotating liquid iron‑nickel outer core surrounding a solid inner core. This motion generates a field comparable to a bar magnet tilted roughly 11° from the rotation axis. The Earth’s magnetic poles are the opposite of its geographic poles, which explains why a compass needle points toward the geographic north. This geomagnetic field forms the magnetosphere, deflecting solar wind and creating auroras. Moreover, the field imprints itself on cooling lava, offering crucial evidence for plate tectonics and magnetic field reversals.
By exploring the diverse materials that produce magnetic fields, we gain insight into the science behind everyday technology and the dynamic forces shaping our planet.
