Upper critical field of a Sm1.85Ce0.15CuO4-y single crystal: Interaction between superconductivity and antiferromagnetic order in copper oxides.
The temperature dependence of the anisotropic upper critical magnetic field, {ital H}{sub {ital c}2}(T), has been determined resistively in antiferromagnetic Sm{sub 1.85}Ce{sub 0.15}CuO{sub 4{minus}{ital y}} single crystals. We observe the first evidence in high-{ital T}{sub {ital c}} copper oxides for the interaction between superconductivity and antiferromagnetic ordering of rare-earth ions; estimates of the exchange coupling {ital J}{approx}0.1 eV and the Ginzburg-Landau coherence lengths {xi}{sub {ital ab}}=79 A and {xi}{sub {ital c}}=14.7 A are obtained. In both Nd{sub 1.84}Ce{sub 0.16}CuO{sub 4{minus}{ital y}} and Sm{sub 1.85}Ce{sub 0.15}CuO{sub 4{minus}{ital y}}, the {ital H}{sub {ital c}2} data above {ital T}{sub {ital N}} can be described by {ital H}{sub {ital c}2}({ital T})/{ital H}{sub {ital c}2}{sup +}(0)=(1{minus}{ital T}/{ital T}{sub {ital c}}){sup 1.6}.