Magnet
A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include the elements iron, nickel and cobalt, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism.
Magnet
In all units, it is convenient to employ two types of magnetic field, B and H, as well as the magnetization M, defined as the magnetic moment per unit volume.Materials that are not permanent magnets usually satisfy the relation M = "χH in SI, where "χ" is the (dimensionless) magnetic susceptibility. Most non-magnetic materials have a relatively small "χ" (on the order of a millionth), but soft magnets can have "χ" on the order of hundreds or thousands. For materials satisfying M = "χH, we can also write B = "μ"(1 + "χ")H = "μ""μ"H = "μH, where "μ" = 1 + "χ" is the (dimensionless) relative permeability and μ =μμ is the magnetic permeability. Both hard and soft magnets have a more complex, history-dependent, behavior described by what are called hysteresis loops, which give either B vs. H or M vs. H. In CGS, M = "χH, but "χ" = 4"πχ", and μ = μ.