Tiny floating magnet detects ultrafaint magnetic fields at room temperature

Researchers have developed a miniature floating magnet that can detect ultra-faint magnetic fields at room temperature, without the need for expensive or bulky equipment. This tiny sensor, described in a paper published in Science, could revolutionize the way we measure weak magnetic signals in various fields.

The sensor consists of a tiny permanent magnetic disk, smaller than a grain of rice, suspended inside a glass vacuum chamber. The disk levitates midair, held in place by magnets overhead and a repulsive force from a graphite plate beneath it. When an external magnetic field causes the disk to tilt, a laser beam reflecting off its surface shifts position, which is detected by a light sensor and converted into an electrical signal.

The magnet's floating design helps to minimize mechanical noise that typically affects conventional sensors. To improve sensitivity, the researchers significantly reduced thermal magnetic noise, also known as Johnson noise, by binding powdered graphite in epoxy to the lower plate. This technique cut the noise by over 70%, enabling the sensor to pick up far weaker signals.

In tests using wire coils, the team generated weak artificial magnetic fields of known strengths. The device demonstrated remarkable sensitivity, achieving a sensitivity of 32 femtoteslas per square root of Hertz. This breakthrough, combined with the sensor's compact size and ability to operate at room temperature and in Earth's magnetic field, makes it a practical alternative to existing devices.

These advancements open up new possibilities for applications in biological sensing, chemical sensing, and fundamental physics research. The researchers at Science emphasize the potential impact of this compact, low-noise magnetometer on various scientific fields.