DIAMAGNETIC MATERIALS--- When brought into an external field, a weak internal B field is induced inside the material that opposes the external field.

PARAMAGNETIC MATERIALS--- Brought into an external field, the atoms weakly align with the field. Liquid oxygen provides a classic demonstration, adhering to the pole faces of a large magnet.

FERROMAGNETIC MATERIALS--- contain "unpaired" electrons whose magnetic moments align with those of electrons in neighboring atoms. When a ferromagnetic material is brought into an external field, it develops a strong internal field due to electron moments aligning with the field. When the field is removed, most of the alignment still remains, and the material is "permanently" magnetized.

Magnetic "charges," also called monopoles.? There does not seem to be any physical reason why fundamental particles that are sources of B should not exist, but none have ever been observed despite intensive searches. All known B fields form closed loops. There are no B fields that radiate outward to infinity from a source, or converge from infinity down onto it.