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 μSr 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 TN=540±5 K in Ca0.86Sr0.14CuO2: below T=360 K, we observe muon-spin precession with a frequency ν(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 Ea=0.39(1) eV. The sublattice magnetization Ms, proportional to ν(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 a more two-dimensional magnetic behavior. In the infinite-chain system Sr2CuO3, the onset of magnetic order was found at T∼5 K with a local field of ∼30 G at the muon site at T→0. The exchange interaction, inferred from susceptibility measurements is on the order of 103 K, implying a remarkable suppression of the ordering temperature with kBTN/J≤0.01 in Sr2CuO3. These results demonstarate clear signatures of low-dimensional magnetic behavior in the CuO chains.