Permanent magnets can be made from many different materials with varying qualities. Each material has distinct strengths and weaknesses in four different categories of magnetism. These four categories are remanence, coercivity, energy product and Curie temperature. There are also four main types of materials for making permanent magnets. These are ferrite, alnico, samarium cobalt and neodymium magnets.
Ferrite permanent magnets are made from the sintered composite of iron oxide and a carbonate mixture of barium and strontium. These materials are used to create fairly inexpensive magnets, such as those needed to make radio antennas. They are also very malleable. They possess a fine quality in their resistance to corrosion but are also very brittle.
Alnico permanent magnets are made when a mixture of aluminum, nickel and cobalt are sintered with iron. The magnets produced in this process strongly resist demagnetization. This gives them a higher rate of coercivity. However, these magnets and ferrite magnets were outdone by rare earth materials used to make samarium cobalt and neodymium magnets in the late 20th century.
Samarium cobalt magnets were first developed in the 1960’s and 1970’s. These magnets, made from rare earths, were far superior to any previous magnets conceived by industry. Some alnico magnets actually had a higher remanence, or pure magnetic strength, than the samarium cobalt variety. However, samarium cobalt far outdid previous magnetic materials in the categories of coercivity and energy product. The latter is essentially a measure of the density of a magnetic field. The similar Curie temperature, or temperature at which a magnet begins to lose magnetic properties, drove researchers to try to develop a stronger magnet from the rare earth neodymium.
They were, at first, disappointed. While magnets made from neodymium were at least equal in remanence to all previous substances and their coercivity and energy product were far higher, the Curie temperature of magnets made from neodymium was a disappointing 400 degrees Celsius, lower even than the poorest kind of ferrite magnet. This meant that the magnet would begin losing magnetic qualities at relatively low temperatures, making it fairly useless for industrial applications. Only later, when someone discovered how to alleviate this problem by adding other rare earths such as terbium to the alloy, would these magnets become desirable in an industrial setting.
Since the development of neodymium magnets in the 1980’s and 1990’s, they have slowly taken over the permanent magnet industry. They are increasingly used in a variety of applications. They have found particular use in much of the advanced technological devices presently pouring out of factories in the forms of MRI machines, cordless tools and various electrical devices. The magnetic power in even a small magnet made from this substance has enabled people to use them in the tiniest applications.