High-performance permanent magnets made of rare earths (Nd-Fe-B) are key components for electric vehicles and wind turbines. The Nd-rich grain boundary that forms during the consolidation process is vital for the performance of the magnets. This study aims to carefully modify the interface of each individual grain by coating its surface. A specially designed sputtering system for granular materials is used to deposit a thin metal film (e.g. copper) on each grain of the loose Nd2Fe14B powder. For optimum magnetic performance and manufacturing, only trace amounts of copper (about 0.1 atomic percent) have a positive effect, so other materials (e.g.neodymium) need to be added to the grain boundary. A uniform coating of the powder surface is achieved by putting the powder in a rotating container that is periodically concussed to avoid agglomerates. The average size of the grains is in the range of 5-10 μm with an applied coating thickness of 3-9 nm of copper. Predicting the coating thickness on individual grains is critical and a calculation method is used that takes into account the periodically changing powder surface exposed to the vapor beam. The current calculation method is extended by considering the local number of particles reaching the exposed powder surface. The evaluation of the thickness and its uniformity is performed by gravimetry, optical microscopy, electron microscopy, energy dispersive X-ray and electrical resistivity measurement. The electrical resistance of the coated grains is measured under external load, whereby a thickness-dependent behavior is to be expected.