LINCOLN, Neb. A scientist at the University of Nebraska has created a plastic magnet by aggregating specially designed organic molecules into a bulk material. Some 13 years of focused research enabled chemistry professor Andrzej Rajca to lay claim to a world "first," ahead of competitors in Japan, Europe and elsewhere in the United States.
"Magnetic polymers were predicted more than 30 years ago, and a large volume of work has been done on this," said Rajca. "It's been a gradual process, one step at a time, making larger and larger molecules with different arrangements of unpaired electrons in order to figure out how to make this polymer." Working with Rajca were his research partner and wife, Suchada Rajca, and doctoral candidate Jirawat Wongsriratanakul.
Magnetic polymers were predicted in 1968 by Japanese theoretical chemist Noboru Mataga. Since then, scientists have created many kinds of microscopic organic magnets based on small crystal molecules, but Rajca's is the world's first organic polymer that can be said to be magnetic.
Unlike crystals, organic polymers are very large, chainlike molecules composed of repeatedly linked smaller carbon-based molecules (hence the term "organic"). Because Rajca's magnets are made entirely of these organic molecules, and include no crystals or metals, his discovery is considered a true plastic magnet.
Rajca began his research at Kansas State University in 1988, but moved his lab to Nebraska in 1992. Since then, he has been investigating the magnetic, conducting and optical properties of various organic molecules with the aim of understanding how the electronic characteristics depend on features as small as a fraction of a nanometer.
Rajca said his goal was to obtain the highest possible spin for organic molecules with extensive dendritic and macrocyclic structures, resulting in very large magnetic moment, albeit at low temperatures (10 Kelvin, or 440° below zero Fahrenheit) and in the absence of oxygen.
So far Rajca has only been able to synthesize a few milligrams of bulk material, "on the order of several milligrams," he said. To make a magnetic polymer takes "many steps in organic synthesis, and each step does not have a perfect yield. So although we begin with a larger amount, we end up with very little in the end."
The team started out by designing organic molecules with unpaired electrons that were exchange-coupled to each other. Consequently, they will align themselves with an externally applied magnetic field so-called "paramagnetism." By aligning the magnetic moments of thousands of these paramagnetic molecules, the research team was able to create a polymer that exerts its own magnetic field.
Rajca is confident that he will be able to overcome the oxygen-sensitivity, low-temperature and low-yield limitations of his plastic-magnet process, and indeed the Japanese theoretician Noboru Mataga predicted 30 years ago that room-temperature operation was theoretically possible. However, Rajca pointed out that his discovery is not a way to make lightweight magnets. Instead, it should be viewed as a basic-science result that will spawn as-yet-unpredicted applications.
The Nebraska team is now focusing on streamlining the processes so that it does not rely on a cold, oxygen-free environment. Rajca is also focusing on cutting manufacturing steps, hoping to increase yields.
"Next is to prepare something that can be handled under ambient conditions, so we don't have to avoid oxygen," he said. "Also, we want something that can be synthesized a little bit easier, so we don't have to go through so many steps and end up with so little." Despite being upbeat on overcoming the limitations of his manufacturing process, Rajca was reluctant to predict just when plastic magnets would find their way out of research labs.
"We are a long way from making a practical material; I would not want to give you a timetable," he said.
An audio recording of reporter R. Colin Johnson's full interview with Andrzej Rajca can be found online at AmpCast.com/RColinJohnson.