Magnetic Excitations in Cr-Ru Superconducting Alloy

We have studied the spin fluctuations in the normal state of a cubic superconductor Cr$_{(1-x)}$Ru$_{x}$ for x$=$0.2. The electron doping created by Ru ions in Cr$_{(1-x)}$Ru$_{x}$ monotonically decreases the antiferromagnetic (AFM) spin density wave (SDW) transition temperature, T$_{N}$. As the Ru fraction increases through x$=$0.17 [1], the long-range SDW order is completely suppressed and the alloy becomes a superconductor. We have conducted a series of inelastic neutron scattering (INS) experiments with Ru concentration of x$=$0.2 with a superconducting transition temperature of Tc $\sim$1.6 K. The SDW fluctuations are found to be commensurate with the magnetic propagation vector of Q$_{AFM}=$(100). At high energy transfers, the strong spin fluctuations appearing near Q$_{AFM}$ reach beyond dE$=$120 meV, not unlike metallic Cr, where spin excitations are very energetic and can reach up to several hundreds of meV [2]. These excitations are also found to be down to energies of dE$=$2 meV. We discuss the possibility that superconductivity found in the Cr-Ru alloy system is unconventional. \\[4pt] [1] K. Chatani and Y. Endoh, J. Phys. Soc. Of Jpn, 72 , 17 , (2003)\\[0pt] [2] E. Fawcett, et. al. Rev. Mod. Phys. 66, 25 (1994)