NEUTRON-SCATTERING OBSERVATIONS ON THE MAGNETIC PHASES OF RARE-EARTH TERNARY SUPERCONDUCTORS

A number of ternary compounds become superconducting even though they contain a chemically ordered sublattice of magnetic rare-earth ions. Studies of the physical properties of these materials have revealed anomalies below T c which have been attributed to magnetic ordering transitions. Using neutron spectrometers at the Brookhaven National Laboratory, a group of us has demonstrated that simple magnetic structures with long-range order do occur, and we have solved some of the magnetic structures of these superconductors. Specifically, we have found that in DyMo6S8 and TbMo 6S8 an antiferromagnetic structure coexists with superconductivity. In two other compounds, ErRh4B4 and HoMo6S8 we have found that the development of ferromagnetism is responsible for the quenching of superconductivity. A study of the critical magnetic neutron scattering near the superconducting → ferromagnetic transitions shows the presence of fluctuations into a state with an oscillatory magnetization of wave length λ=100 Å.