Magnetic Materials:

A few substances cause magnetic lines of flux to bunch closer altogether than they are in the air; other materials cause the lines of flux to spread farther separately. The first type of material is ferromagnetic. Substances of this kind are, "magnetizable." The other type of material is termed as diamagnetic. Dry wood, wax, bismuth, and silver are illustrations of substances which reduce magnetic flux density. No diamagnetic material decreases the strength of a magnetic field by anywhere near the factor which ferromagnetic substances can raise it.

The magnetic characteristics of a substance or medium can be quantified in two significant but separate ways: permeability and retentivity.