MUON-SPIN-ROTATION MEASUREMENTS IN INFINITE-LAYER AND INFINITE-CHAIN CUPRATE ANTIFERROMAGNETS - CA0.86SR0.14CUO2 AND SR2CUO3

We have performed zero-field muon-spin-rotation measurements of the ''infinite-layer'' cuprate compound Ca0.86Sr0.14CuO2 and the ''infinite-chain'' system Sr2CuO3. A spontaneous magnetic field from the ordered Cu moments is observed below T(N) = 540 +/- 5 K in Ca0.86Sr0.14CuO2: below T = 360 K, we observe muon-spin precession with a frequency nu(T --> 0) = 16 MHz (corresponding to a local field of 1.2 kG). The precession signal is replaced by a rapid depolarization above T = 360 K due to the onset of muon diffusion. The hopping rate followed an Arrhenius law, with an activation energy of E(alpha) = 0.39(1) eV. The sublattice magnetization M(s), proportional to nu(T), showed a slower decay with increasing temperature in Ca0.86Sr0.14CuO2, compared with that observed in La2CuO4 and Sr2CuO2Cl2, indicating that a wider CuO2-layer separation results in more two-dimensional magnetic behavior. In the infinite-chain system Sr2CuO3, the onset of magnetic order was found at T approximately 5 K with a local field of approximately 30 G at the muon site at T --> 0. The exchange interaction, inferred from susceptibility measurements is on the order of 10(3) K, implying a remarkable suppression of the ordering temperature with k(B)T(N)/J < 0.01 in Sr2CuO3. These results demonstrate clear signatures of low-dimensional magnetic behavior iu the CuO chains.