Quasi-continuum excitation in Co-doped CaRuO3.

Spin-1/2 systems provide a unique platform to study the interplay between magnetism and quantum mechanics that often depict novel properties, such as quantum spin liquid or singlet-to-triplet transition. In this presentation, we report an interesting observation of singlet-to-triplet transition in Co-doped CaRuO3, even though none of the magnetic atoms (Co or Ru) exhibit spin-1/2 properties. What we have found that as Co atom gradually replaces Ru in CaRuO3, the system tends to develop a localized excitation around Q$=$1 A$^{-1}$ at 5.9 meV at low temperature. At roughly 20{\%} doping percentage of Co, the inelastic excitation at low temperature is well described by singlet-to-triplet transition of S$=$1/2. As the measurement temperature increases, the localized excitation fades into a sort of Q-independent background that becomes stronger as a function of temperature. This behavior is also well manifested by ac susceptibility measurements where the dynamic susceptibility tends to get stronger as the temperature increases. Our analysis suggests that Co-doping in CaRuO3 locally creates 3$d^{7}$ electronic configuration, which can be described by S$=$1/2 in this disordered system.