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New Materials

A different type of magnet

Graphite developed by a Brazilian and Uruguayan research team has magnetic properties

Researchers from the Federal University of Sao Carlos (UFSCar) and the University of the Republic (Udelar), in Montevideo, Uruguay, have managed to transform a pure organic and non-metallic element – carbon graphite – into a magnet by way of a cheap chemical treatment. The new material opens up pathways for the manufacture of magnetic devices such as sensors and detectors used in areas that run from space engineering to medicine. Up until now European researchers have been able to manage this feat, but by using techniques that are much more expensive and complex, as is the case of the method developed by a German research team that made use of bombarding using a proton beam, generated by a nuclear reactor, in order to produce the magnetism in the graphite. “Besides being a much more expensive and complex process, and as yet not totally explained, the magnetism obtained by them is approximately ten times smaller than that of our carbon” explains one of the inventors, the materials engineer Fernando Manuel Araújo-Moreira, a professor at the Physics Department of UFSCar, and the coordinator of the work in Brazil.

The importance of the invention lies in the fact that, for some time now, the scientific community believed that a magnetic material must by obligation contain atoms of metallic elements such as iron, cobalt and nickel. Research carried out by scientists from the Brazilian and Uruguayan universities has demonstrated the contrary because the graphite only possesses carbon atoms. “We confirmed in the arrangement of the carbon atoms, which is the basic element of all organic structures, a new property, that of magnetism” advised professor Araújo-Moreira. The patent for the invention, named Process for the preparation of magnetic graphite materials and materials thus prepared, was requested by the Foundation of Institutional Support of UFSCar at the National Industrial Property Institute (INPI) and has as co-title holders the two universities. The list of inventers include, as well as professor Araújo-Moreira, the doctorate student Helena Pardo and professor Álvaro Mombrú, the coordinator of the work in Uruguay.

The new material has also had repercussions in the business world. The UFSCar researchers are in negotiations with the Brazilian company named Nacional de Grafite, with its head office in the town of Itapecerica, in Minas Gerais State. The company is the major world manufacturer of natural graphite crystals with a capacity to produce 46,000 tons per year, half of which is sold to clients abroad. “The agreement forecasts the investment of around R$ 300,000.00 for the continuity of our research, now on an industrial scale, looking towards technological applications” says Araújo-Moreira.

The research for obtaining organic materials with magnetic properties is very recent and was only initiated at the beginning of the last decade. According to the UFSCar researcher, up until today scientists throughout the entire world have been asking themselves if it was possible to produce a purely organic material with magnetic properties. “Some groups have already managed to synthesize organic compounds endowed with magnetism, however only in microscopic quantity and with very weak signals, which placed the results in doubt” says Araújo-Moreira. “Our team has managed to manufacture macroscopic quantities of magnetic graphite, which, although very small, can be seen with the human eye. As well as this, this new material is endowed with ferromagnetism, a property that guarantees it to have permanent magnetism and the capacity of attracting metals. Another proof of this is that it is strongly attracted by a magnet at a distance of around 10 centimeters” he advised.

The ferromagnetism of the graphite produced by the UFSCar and Udelar researchers also has the advantage of maintaining itself stable at room temperature. This is important because all magnets obtained from carbon in the past only presented ferromagnetism at very low temperatures, close to absolute zero (-273°C), which had limited its field of application. The material discovered by the teams of professors Mombrú and Araújo-Moreira is stable over a temperature range because it possesses a magnetic signal that does not suffer degradation with the passing of months. The sample of 0.5 square millimeters (0.5 mm2) by the researchers in May of 2004 has continued with its magnetism unaltered during the following ten months of it having been synthesized. This property is fundamental for the construction of devices and equipment of high durability.

If the research results, done on the laboratory scale, were to be highly successful on the industrial scale, the discovery of a graphite with magnetic properties should trigger a new phase in materials engineering. As it is a recently discovered material, it is not yet known exactly in which areas it can be applied. The researchers believe that the material can be used in a large number of high technology devices, as sensors, activators (devices that move in a production line of semi-conductors or on banks of clinical analyses, for example), detectors, as well as equipment in the aerospace, chemical and electronics sectors, as well as in telecommunications and biotechnology. By being, for now, the only 100% biocompatible magnetic material, the magnetic graphite also has chances of being used in medicine. “Pacemakers and cardiac valves are based on magnetic processes and a 100% organic material, which does not cause rejection in the human organism and is magnetic, would allow new advances with the devices” advised professor Araújo-Moreira. “Furthermore, Canadian researchers are beginning to research the use of magnetic graphite for the treatment of cancer.”

Accepted for publication in the month of March by the scientific magazine Physical Review B – Rapid Communications, the study has already produced good repercussions. “If it is proven that the results are reproductive and that the sample does not contain iron impurities, this is a major discovery in the area of materials science” says the Russian researcher Tatiana Makarova, from the Umea University, in Sweden, considered to be one of the top researchers in the area of magnetic carbon. “The differences between the magnetic carbon produced by professor Araújo-Moreira and other similar materials are in the primary magnetic effect and in the fact that his production method is cheap” she stated.

The next challenge for the scientists is to demonstrate that it is possible to produce magnetic carbon with the same characteristics – strong signal at room temperature and stable over a long period of time – in large quantities and to develop an industrial process. In the negotiations with the company Nacional de Grafite also forecast is joint work to be submitted to research development agencies with the objective of developing supports for catalysts based on magnetic carbon. These supports would be used to accelerate chemical reactions that generate chemical products.

Simple and economical
In order to manufacture the magnetic graphite, Araújo-Moreira and his colleagues made use of an unprecedented process, different from all of those that had been done up until then. “We’re dealing with a very simple method in a controlled chemical process of oxidation-reduction in the vapor phase, which, by being economical and using low cost commercial reagents, would allow, in the future, its manufacture and commercialization by small companies.”

The production in the laboratory is done in an oven with controlled atmosphere, where two crucibles (ceramic receptacles that withstand high temperatures), one of them with commercial graphite in powder form and the other with an oxide of a metal, such as, for example, copper oxide (CuO). The oven is maintained hot at 1,200°C during twelve to sixteen hours. At this temperature the copper oxide decomposes and is reduced to copper metal. The liberated oxygen brings about the controlled oxidation of the graphite and introduces into its structure small defects, in the form of cavities, which, the researchers assume, are responsible for conferring magnetic properties to the mineral. “In truth, the origin of the phenomenon of magnetism in this material has not yet be fully explained” adds  professor Araújo-Moreira. The researcher pointed out that the most recent data obtained by way of computer simulations indicates the appearance of strong ferromagnetism as a consequence of the lack of carbon atoms in the atomic structure typical of graphite. The simulation removed an atom of carbon and it became magnetic. In the laboratory, probably the absence of these carbon atoms in the graphite structure is achieved by way of a chemical attack.

The discovery of the new material is the result of three years of intense research. “Everything began in 2001, during the post-doctorate work of the Uruguayan researcher Álvaro Mombrú at the Physics Department of UFSCar, under my supervision. It was then that the idea that we study the physical and chemical properties of graphite was born, from which was derived the discovery of the chemical process that led to obtaining magnetic graphite” recalls Araújo-Moreira. During that year, the American scientific magazine Nature published an article that showed the possibility of the manufacture of a variation of pure carbon that would be magnetic. The third integrant of the team, the Uruguayan chemist Helena Pardo, is currently studying for her doctorate degree at the Physics Institute of the Chemical School of the University of the Republic of Montevideo, Uruguay, under the double supervision of professors Araújo-Moreira and Mombrú.

Detailed description
In order to certify that the material produced really had unique characteristics, the team submitted the sample to an extensive battery of tests, carried out at the Semiconductor Laboratory of the Physics Department of UFSCar, work carried out by the researcher Giovanni Zanelato, and at the Inter-Disciplinary Laboratory of Electrochemistry and Ceramics (Liec), with professor Édson Leite, from UFSCar, and with the collaboration of professor Oscar Ferreira de Lima, from the Materials and Low Temperatures Laboratory (LMBT) of the Physics Institute of the State University of Campinas (Unicamp). The experiment carried out in this last mentioned laboratory, made with a Squid magnetometer (Superconducting Quantum Interference Device) measured the variation of magnetization of the material with temperature. This test demonstrated that the graphite ‘s magnetism remained up until 80°C.

Besides the laboratory examinations that demonstrated the effectiveness of the chemical method, the sample was submitted to chemical analysis with an atomic absorption spectrophotometer that verified the purity of the material, verifying the absence, in undesirable levels, of any ferromagnetic metallic impurities such as iron, cobalt and nickel. A complementary examination by a sweep electronic microscope confirmed the existence of these cavities in the graphite, brought about by chemical attack. Finally, observations carried out with a microscope of atomic and magnetic forces shows, in images bi and tri-dimensional, the existence of magnetic trails in the graphite, characteristics of ferro-magnetic metals, that is material that attract metals.