In the case of sintered magnets, the magnet material is in its highest performance composition. We speak about this type of magnets, if the main material (e.g. NdFeB) is not being mixed with a further material. They are contrary to the today mainly spread plastic bonded magnets.
In sintered form, magnets achieve its strongest attraction (remanence) and its highest consistency (coercivity field strength), so they are highest performance. Mainly the homogeneity as well as resistance are a characteristic for good quality.
When speaking about sintered magnets we divide it in sturdy hard ferrite magnets and in high performance rare-earth magnets.