Magnetically Hard Material

A hard magnetic material, such as ALNICO (an alloy of aluminium, nickel and cobalt), has high permeability, high retentivity and very high coercivity of the orders of 1 tesla and 10⁴ ampere per metre respectively.

Such material have a large zero-field magnetization, and large reverse field is needed to demagnetize it. Its hysteresis loop is very broad. Such a material can be made into a permanent magnet, that is, its magnetization will persist indefinitely if it is subsequently exposed only to

weak magnetic fields.