PORTLAND, Ore. The world's highest temperature superconductors share an unusual affinity for magnetism, according to researchers in the U.S. Earlier this month, high-temperature superconducting iron-compounds with lanthanum and arsenic were separately discovered by Japanese and Chinese researchers. Now, U.S. researchers have confirmed those results, heralding a new generation of "supermagnets" for magnetic-resonance imaging (MRI) machines, superconducting electric motors, power-generators and -transmission lines.
Japanese researchers at the Nihon University, the Frontier Research Center, and the Tokyo Institute of Technology showed that iron compounded with fluorine-doped lanthanum oxide and arsenic could superconduct at temperatures as high as 44 degrees Kelvin (-380 degrees Fahrenheit), while the Institute of Physics in Beijing reported an even higher temperature of 55 degrees Kelvin (-360 Fahrenheit). Now, U.S. researchers at the Commerce Department's National Institute of Standards and Technology (NIST) have found that the new materials have magnetic similarities with the highest temperature copper superconductors that only require cooling by liquid nitrogen (77 degrees Kelvin, or -321 degrees Fahrenheit), which is much easier to supply than low-temperature superconductors that require liquid helium cooling to 4 degrees Kelvin (-452 degrees Fahrenheit).
Tests at NIST's Center for Neutron Research show that the new iron-based materials are similar to copper-based high-temperature superconductors, both of which share a critical interplay between magnetism and superconductivity. Only a few magnetic impurities in low-temperature materials can cancel their ability to superconduct, but the new iron-based compounds react similarly to copper-based superconductors in the presence of magnetism, according to NIST, which used intense neutron beams to plumb the atomic structure of the new magnetic material.
Using neutron beams to probe an iron-based sample supplied by the Chinese scientists, NIST found layers of magnetic moments similar to those found in copper-oxide superconductors--individual regions of bar magnets interspersed with layers of nonmagnetic material. The NIST researchers predict that the magnetic properties of this new class of iron-based superconductors will tolerate many different chemical substitutions, which should permit the superconducting properties to be tailored for different applications.
Separately, the National High Magnetic Field Laboratory at Florida State University, working with colleagues at Oak Ridge National Laboratory, found that the world's strongest magnetic fields at their facility could not quell the superconducting properties of the new material, which kept superconducting all the way up to 45 tesla. No other superconductors have been able to tolerate magnetic fields that high, making the new iron-based materials candidates for generating magnetic fields even stronger than those possible today.