ELECTRONIC, STERIC, AND DILUTION EFFECTS ON THE MAGNETIC-PROPERTIES OF SM2-XMXCUO4-Y (M = CE, Y, LA, AND SR) - IMPLICATIONS FOR MAGNETIC PAIR BREAKING

Recent data suggest that the high-T(c) compound Sm2-xCexCuO4-y presents considerable difficulties for conventional theories of magnetic pair breaking. We report results of x-ray diffraction, superconducting-quantum-interference-device magnetization, and resistivity measurements for single-phased polycrystalline specimens of Sm2-xMxCuO4-y (M = Ce, Y, La, and Sr) for various x and y. In each case, the magnetic Sm3+ ions are diluted by a nonmagnetic species: isovalent Y3+ and La3+, or nonisovalent Ce4+ and Sr2+. Rare-earth magnetic order occurs below 6 K in Sm2CuO4; isovalent dilution with M = Y results in a depression of the Neel temperature T(N) at an initial rate (1/T(NO))(dT(N)/dx) = -0.0110/at. %, a result that can be well described by a simple theory of magnetic dilution. Isovalent dilution with M = La reveals a small steric effect. Nonisovalent dilutions are interpreted in terms of concentration-dependent exchange interactions; electron and hole dopings result in depression and enhancement of the rare-earth exchange coupling, respectively. Our results (j less-than-or-similar-to 6 meV) indicate that the coupling between rare-earth ions and superconducting electrons is probably much smaller than previously suggested, and that conventional magnetic pair-breaking theory adequately describes these materials. Some magnetic features suggestive of a subtle transition in the range x = 0.10-0.15 in the insulating M = Ce series are also observed.