Spin dynamics in an electron-doped high-T_c superconductor

We have performed inelastic neutron-scattering measurements on an electron-doped superconductor, Pr_{1 x}LaCe_xCuO₄ to clarify the doping dependence of spin correlations. In measured samples with x=0.09, 0.11, 0.13, 0.15 and 0.18, the low-energy spin correlations are commensurate, unlike in hole-doped systems, which have incommensurate spin correlations. Upon electron doping, the commensurate peaks centered at the (π, π) reciprocal position are more drastically broadened at a higher energy, suggesting a reduction of slope of spin excitations ω/q namely an effective nearest exchange constant J_eff.