Diamond magnetometer combines extreme sensitivity with small size

MIT Technology Review : The Zeeman effect can be used to measure the strength of a magnetic field by looking for spectral changes in light that passes through the field. Thomas Wolf of the University of Stuttgart in Germany and his colleagues have used the Zeeman effect to make a new magnetometer that is comparable to the best in the world but much smaller. The size of a magnetometer is important because magnetic field strength is proportional to the inverse cube of the distance from the source. What enabled Wolf’s team to make a small magnetometer was nitrogen diamond defects: When a nitrogen atom replaces a carbon atom in a diamond crystal, it produces an extra unbound electron. When the electron is excited by a laser, it fluoresces at a particular frequency, which is then altered by any magnetic fields nearby. Wolf’s team created a microscopic diamond that had several billion diamond defects, which made the signal large enough to be detected. After controlling for other effects, they were able to detect a magnetic field with a strength of only 100 fT. They believe that they can increase the sensitivity by up to two orders of magnitude. Perhaps more importantly, because of its small size, the magnetometer can already be used to measure magnetic fields in places that were previously unreachable.