Nanomagnets Under The Microscope

A fluorescent molecule that glows brighter in the presence of weak magnetic fields can help map the fields around nanoparticles, according to a study in Nano Letters (DOI: 10.1021/nl202950h). When scientists design new magnetic nanoparticles, such as those in memory chips, they have to collect detailed information about the magnetic fields in the vicinity of the particles. Adam E. Cohen, a chemist at Harvard University, and his colleagues developed a simple method for making those measurements based on the properties of an indicator molecule consisting of phenanthrene tethered to N,N-dimethylaniline. The team showed that by applying a magnetic field, they could increase the intensity of light that the molecule emitted after UV radiation excited it. For example, in a magnetic field of 0.15 tesla—slightly higher than typical refrigerator-magnet strength—the compound glowed about 80% brighter than it did in the absence of a field. When the chemists used that property to map magnetic fields around iron particles, they found that they could detect field strengths as small as about 0.1 millitesla.