One is sintered neodymium magnets, the other is bonded neodymium magnets. The sintered neodymium magnets is produced by powder metallurgy. It is made from the alloy of neodymium, iron, boron etc which form the Nd2Fe14B crystalline structure. Nd2Fe14B is composed of 2 rare earth atoms, one boron atom and 14 iron atoms.
Besides the main-phase Nd2Fe14B (in neodymium magnet alloy), there are some small quantities of neodymium-rich phase (rare earth-rich phase), boron-rich phase and others..