The strongest magnets available nowadays are the neodymium magnets, made of a combination of neodymium, iron, and boron (abbreviated: NdFeB). They are called rare earth because their composition elements are found in the “Rare Earth" or Lanthanides portion of the Periodic Table of Elements.
First developed in the 1980’s, neodymium magnets are characterised by exceptionally strong magnetic properties by even better resistance to demagnetisation, unlike most other types of magnets. NdFeB magnets are extremely powerful by volume and will retain magnet properties for decades (they are considered permanent magnets, even if they are not literally permanent).
This group of magnetic products provides the highest available magnetic energies of any material. NdFeB magnets require extremely high magnetising fields. They are are mechanically week, but magnetically very strong. Two magnets can snap together with enough force to chip or shatter on impact.
Sintered NdFeB magnets are hard and brittle. To protect the magnet from corrosion and to strengthen the brittle magnet material, it is highly recommended for the magnet to be coated.
NdFeB magnets allow small shapes and sizes and have multiple uses in science, engineering and industry. Various kinds of sintered NdFeB magnets in specific shapes and sizes such as blocks, cubes, cylinders, discs, spheres, rods, rings can be ordered.
There currently aren't any known negative health effects from handling NdFeB magnets.
George Toncescu is a science enthousiast. He created http://www.neodymiummagnets.info/ as a placeholder of articles on neodymium magnets, the most powerful magnets in the world.