Magnetic ordering in rare-earth ternary superconductors

A review is given of current neutron scattering studies of rare-earth(R) ternary superconductors: RMo6X8(X = S or Se) and ErRh4B4. Most of these compounds develop antiferromagnetic long-range order which coexists microscopically with superconductivity. Two compounds, HoMo6S8 and ErRh4B4, become ferromagnetic causing the destruction of superconductivity. In ErRh4B4, both superconducting and ferromagnetic regions are simultaneously present between 0.9 and 1.20K but microscopic coexistence is not indicated. However, in this temperature range, magnetic fluctuations occurring in the superconducting regions take the forms of a magnetic spiral with a wavelength of approx. 100 A in order to accommodate superconductivity. This observation is in good agreement with the theoretical predictions of Blount and Varma