Finite-size effects in the quasi-one-dimensional quantum magnets Sr2CuO3, Sr2Cu0.99M0.01O3 (M = Ni, Zn), and SrCuO2

We studied the finite-size effects on the magnetic behavior of the quasi-one-dimensional spin S = 1/2 Heisenberg antiferromagnets Sr2CuO3, Sr2Cu0.99M0.01O3 (M = Zn and Ni), and SrCuO2. Magnetic susceptibility data were analyzed to estimate the concentration of chain breaks due to extrinsically doped defects and/or due to slight oxygen off-stoichiometry. We show that the susceptibility of Sr2Cu0.99Ni0.01O3 can be described by considering Ni2+ as a scalar defect (S-eff = 0) indicating that the Ni spin is screened. In Sr2Cu0.99Zn0.01O3 susceptibility analysis yields a defect concentration smaller than the nominal value which is in good qualitative agreement with crystal growth experiments. Influence of doping on the low-temperature long-range spin ordered state is studied. In the compound SrCuO2, consisting of zigzag S = 1/2 chains, the influence of spin frustration on the magnetic ordering and the defect concentration determined from the susceptibility data is discussed.