Ferromagnetic materials are commonly known as ‘magnetic materials’. These materials, again, can be divided into various categories, each showing different properties and in some cases, new properties lead to new understanding of the physics of the materials. Often, these open up new applications. This is the reason why magnets are still exciting and extremely important to the progress of industry and modern life.
In a ferromagnetic material, all the magnetic moments of the individual atoms or ions are aligned parallel to some particular direction. In 1907, Weiss postulated that there must exist an effective internal magnetic field of force which pulls the neighbouring atomic magnetic moments into line. This spontaneously produced field is extremely powerful and can overcome the disordering effect of temperature (provided this is not too high) and is responsible for some remarkable magnetic properties. For example, in iron, this internal magnetic field is as high as 103 Tesla. Compare that to the highest magnetic field artificially created, which is in the range of 102 Tesla. Application of high magnetic fields to materials reveals exciting information about the internal mechanism of matter. Magnetism plays a very important part in understanding the properties of matter. For example, a magnetic field is used to focus and accelerate the charged particles in giant particle accelerators which cover a few miles, to do important research on particle physics or the big bang theory.
What about Columbus? In the four thousand years old history of humanity's quest for knowledge and innovation, magnets have played a crucial role. Magnetic compasses were routinely manufactured in China in the middle ages. Figure 3 shows a print from a tapestry from approximately 1637 AD. This shows the first magnet manufacturing plant on this planet, where magnetic needles for compasses were made by craftsmen. Nowadays, magnets are employed in a huge number of this planets' major industries ... for example motors, generators, magnetic recording, data storage etc. The truth is that the magnet industry is not only alive and well , but it forms the basis of a major world industry that is experiencing above-average growth. The size of this market is hundreds of billions of dollars. Yet the question remains, do we know enough to explain why magnetism occurs in materials? Can we predict or design magnets to solve our application needs? The answer is that our present day understanding about magnetism even in iron, is still incomplete.
Although the study of magnetism is very old, remarkable progress has been made only in the last century. In the 19th century, 1819 to be exact, Oersted’s discovery showed a connection between electricity and magnetism by demonstrating that the torque on a compass needle was caused by a nearby electric current. This discovery opened up people's imagination. This led to a number of inventions, including moving coil meters to measure current and voltage. Then the electromagnet was invented by Sturgeon in 1825. This was followed by the invention of loud speakers, permanent magnet d.c. motors and many more based on the simple principle, where electrical energy is converted to mechanical energy. These discoveries made the ingenious inventor Michael Faraday believe that the converse was possible - that an electric current could be produced by a magnetic field. It is feasible from the energy conservation law of physics. It is also true that permanent magnets are a type of portable source of stored energy and the energy can be transformed from one form to another. In 1831 Faraday proved that his speculation was right and this gave birth to the subject of electromagnetism, leading to the invention of the electric power generator. That is probably the most remarkable industrial innovation of all time, and led to the modernisation of society. This discovery has also had a tremendous effect on the history of mankind. The time-varying magnetic field which creates current led Maxwell to imagine the existence of a time-varying electric field ( in other words the alternating current) and the postulation of his extraordinary Electromagnetic Theory in 1864. Nicola Tesla put this theory into application and the General Electric Corporation let Tesla design and construct the first A.C. generator on Niagara Falls in the USA. What happened in Europe during that period? Hertz in Germany proved Maxwell’s electromagnetic theory that the electrical signal can be propagated through space. Marconi devised the radio communication equipment which gave birth to our telecommunication era.
What are the other achievements with magnets? The list is enormous. Let’s just mention a few very smart ones ........magnetically levitated trains, computer memories, data storage disks and tapes, audio-video tapes, credit and cash cards, various types of sensors and devices applicable in the telecommunication, medical and consumer markets. The principle and the applications are so fascinating that I have devoted my research for the last twenty years to the applied magnetics area. In these two decades I have observed a fantastic growth and evolution in the number of industrial applications of magnets and magnetism. At the University of Limerick, testing and fabrication facilities to investigate new magnetic materials and their application have been set up under the Magnetics Research Laboratory (MRL). One research project at MRL concerns the development of magneto-optical (M.O.) data storage media, using a garnet-type of ferrite material, which would be able to store 1 Gigabyte of Read/Write memory. This means that you will be able to store about 106 typed pages in a single M.O. disk. Research is also underway on the design of new types of sensors and magnetic materials for power electronics, data communication, telecommunication and quality control applications.
Memory elements are also being developed using advanced GMR alloys which could challenge the existing dynamic random-access memory (DRAM) chips. Magnetoresistive random access memory (MRAM) with 16 kilobits of storage have already been demonstrated (see Figure 4). Designs of MRAM chips with up to a million bits are now in progress. These devices will be competitive with DRAM technologies, because of their inherent simplicity of processing, non-volatility, static storage and non-destructive readout. In this technology, the exploited magnetic property spans only a few atomic spacings. In other words, information bits i.e. logic ‘0’ or ‘1’ states can be written within a length of a nanometer or less, i.e. a much higher data density would be attainable. We stand on the verge of a revolution in which this new phenomenon will be exploited and explained.
Would you like to take part in the fascinating quest for this ‘action at a distance’ and use the knowledge as a vehicle for carrying out some exciting experiments? In the study of Physics, a very old science, you might find all of that in the shape of a phenomenon called ‘magnetism’.
Zakia Rahman is a Lecturer in Physics. Her research interests are in electromagnetic materials and technology.
