Magnetizing rare‐earth alloy magnets at elevated temperatures

It is well known that high magnetic fields are needed to fully magnetize rare‐earth based magnets. Even with the conventional magnetizing process employing a large amplitude magnetic pulse (mp), this poses practical difficulties and limits the number of poles and various application specific pole designs required in a magnet. On investigating magnetizability of these magnets, it was concluded that magnetizing can be effectively performed at much lower magnetic fields than normally needed if the temperature of the magnet during the magnetizing process is raised and maintained within a predetermined range. In an experiment, an anisotropic melt‐spun Nd‐Fe‐B magnet of dimension 1×1×0.73 cm³ (easy‐axis along the shorter dimension) was fully magnetized at a temperature between 90 and 110 °C using a mp of amplitude 22.8 kOe. The same sample at room temperature required a mp of amplitude above 42 kOe to get fully magnetized. Similar data for sintered Sm‐Co and sintered as well as rapidly quenched isotropic Nd‐Fe‐B alloys are presented. The optimum ranges of temperatures are explained as a result of thermal deterioration on the magnet’s intrinsic coercivity and remanence properties, and the limiting effect of demagnetizing field on the magnetizing process.