Permanent magnets are those objects that are magnetized and will stay magnetized forever. One can make a permanent magnet by taking a hard ferromagnetic substance, like hard iron, lodestone, cobalt, and a number of rare earth metals, and magnetizing it strongly. Soft ferromagnetic substances may gain a temporary magnetic field, but will tend to lose it rather quickly. Electromagnets, on the other hand, consist of coils of wire that gain a magnetic field when electricity is run through it, but lose it immediately when the electricity ceases.
You can measure either the overall magnetic strength of a material, known as its magnetic moment, or its local strength, known simply as its magnetization. The magnetic moment can be calculated for a substance depending on whether it contains an inherent magnetism or a magnetism caused by an electric current. If the magnetism is inherent, the magnitude of each elementary particle within the material can be measured and the net moment can be determined. If caused by an electric current, one has to track the magnetism of the electrons flowing through the object.
