Spintronics Keeping track of spin transport inside a spintronic device is challenging. Du et al. came up with a method involving diamond nitrogen-vacancy (NV) centers, which can act like tiny, very sensitive magnetometers. The authors placed diamond nanobeams containing the NV centers in close proximity to the sample. This allowed them to measure the spin chemical potential of spin waves—so-called magnons—with nanometer resolution in the material yttrium iron garnet. Because NV centers are also sensitive to temperature, the method may be of use in spin caloritronics. Science , this issue p. [195][1] [1]: /lookup/doi/10.1126/science.aak9611