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Antiferromagnetic excitations in single crystals of Pr2 Ce Cu04~, Nd, "Ce"Cu04~, and Sm2 Ce Cu04~were investigated as a function of Ce concentration using Raman scattering at room temperature.The introduction of electrons by Ce doping significantly broadens the twomagnon peak in the B&g mode, indicating that zone-boundary magnons become damped with increasing Ce concentration. The existence of broad spin-pair-excitation spectra in the B,~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~"Ce Cu04~is not affected by doping up to x=0.2. This is similar in behavior to the Sm& "Ce Cu04~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 in La2 "Sr"Cu04~. The Raman spectra in Pr2 Ce Cu04 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.

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Magnetic flux density distributions in a Bi2Sr2CaCu2Ox superconducting crystal for fields perpendicular to the bc plane are observed by a magneto-optical technique. It is recognized that flux is pinned at the low angle grain boundary while barely pinned at the high angle boundary or in the intragranular regions. The contributions of the low angle boundary to the critical current density and the magnetization are estimated from the magneto-optical results by using a flux pinning model, and then compared with the results of magnetization measurements.