Measuring faint magnetic fields is useful in a number of areas, including mapping brain activity, monitoring hearts and probing fundamental physics. Typically, picking up such weak signals requires expensive or bulky equipment, such as liquid-helium cooling tanks or specially shielded rooms that block out Earth’s magnetic field.

In a paper published in the journal Science, researchers report creating a miniature floating magnet that detects these faint signals at room temperature.

To build their magnetometer, the team suspended a tiny permanent magnetic disk, smaller than a grain of rice, inside a glass vacuum chamber, where it levitated in midair. An overhead stack of magnets pulled the disk upward against gravity, while a graphite plate beneath it provided a repulsive force to help stabilize it.