Neodymium magnets, the correct definition is Neodymium-Iron-Boron (shortcut NdFeB magnets), have the highest adhesion force at smallest volume. These are often referred to as “super strong magnets” or “super adhesion magnets”.
Magnets are made from isotropic or anisotropic strontium ferrite
They comply with the European directive DIN EN 71 for use in toys since they contain a significantly lower proportion of heavy metals compared to barium ferrite magnets