RAMAN-SCATTERING FROM SPIN FLUCTUATIONS IN PR2-XCEXCUO4-Y, ND2-XCEXCUO4-Y, AND SM2-XCEXCUO4-Y

Antiferromagnetic excitations in single crystals of Pr(2-x)Ce(x)CuO4-y, Nd(2-x)Ce(x)CuO4-y, and Sm(2-x)Ce(x)CuO4-y were investigated as a function of Ce concentration using Raman scattering at room temperature. The introduction of electrons by Ce doping significantly broadens the two-magnon peak in the B1g mode, indicating that zone-boundary magnons become damped with increasing Ce concentration. The existence of broad spin-pair-excitation spectra in the B1g and B2g modes at x = 0.15 suggests that the short-range spin fluctuations persist in these electron-doped superconductors. The energy of the spin-pair-excitation peak in Pr(2-x)Ce(x)CuO4-y is not affected by doping up to x = 0.2. This is similar in behavior to the Sm(2-x)Ce(x)CuO4-y system up to x = 0.17. The absence of softening of the short-wavelength magnons in these systems is in marked contrast to the magnon softening behavior inLa(2-x)Sr(x)CuO4-y. The Raman spectra in Pr(2-x)Ce(x)CuO4-y make no distinction between the superconducting and the metallic regions. The highly damped magnetic-excitation spectra support the picture that the spin-spin correlation length in the present systems decreases gradually with increasing Ce concentration.