Muon-spin-rotation measurements in infinite-layer and infinite-chain cuprate antiferromagnets: Ca0.86Sr0.14CuO2 and Sr2CuO3

Abstract

We have performed zero-field muon-spin-rotation μSr measurements of the ‘‘infinite-layer’’ cuprate compound ${\mathrm{Ca}}_{0.86}$ ${\mathrm{Sr}}_{0.14}$ ${\mathrm{CuO}}_2$ and the ‘‘infinite chain’’ system ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_3$. A spontaneous magnetic field from the ordered Cu moments is observed below ${\mathit{T}}_{\mathit{N}}$=540±5 K in ${\mathrm{Ca}}_{0.86}$ ${\mathrm{Sr}}_{0.14}$ ${\mathrm{CuO}}_2$: 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 ${\mathit{E}}_{\mathit{a}}$=0.39(1) eV. The sublattice magnetization ${\mathit{M}}_{\mathit{s}}$, proportional to ν(T), showed a slower decay with increasing temperature in ${\mathrm{Ca}}_{0.86}$ ${\mathrm{Sr}}_{0.14}$ ${\mathrm{CuO}}_2$, compared with that observed in ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$ and ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_2$ ${\mathrm{Cl}}_2$, indicating that a wider ${\mathrm{CuO}}_2$-layer separation results in a more two-dimensional magnetic behavior. In the infinite-chain system ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_3$, 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 ${10}^3$ K, implying a remarkable suppression of the ordering temperature with ${\mathit{k}}_{\mathit{B}}$ ${\mathit{T}}_{\mathit{N}}$/J≤0.01 in ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_3$. These results demonstarate clear signatures of low-dimensional magnetic behavior in the CuO chains.