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The S=1/2 Heisenberg spin chain compound SrCuO2 doped with different amountsof nickel (Ni), palladium (Pd), zinc (Zn) and cobalt (Co) has been studied bymeans of Cu nuclear magnetic resonance (NMR). Replacing only a few of the S=1/2Cu ions with Ni, Pd, Zn or Co has a major impact on the magnetic properties ofthe spin chain system. In the case of Ni, Pd and Zn an unusual line broadeningin the low temperature NMR spectra reveals the existence of an impurity-inducedlocal alternating magnetization (LAM), while exponentially decayingspin-lattice relaxation rates $T_1^{-1}$ towards low temperatures indicate theopening of spin gaps. A distribution of gap magnitudes is proven by a stretchedspin-lattice relaxation and a variation of $T_1^{-1}$ within the broadresonance lines. These observations depend strongly on the impurityconcentration and therefore can be understood using the model of finitesegments of the spin 1/2 antiferromagnetic Heisenberg chain, i.e. pure chainsegmentation due to S = 0 impurities. This is surprising for Ni as it waspreviously assumed to be a magnetic impurity with S = 1 which is screened bythe neighboring copper spins. In order to confirm the S = 0 state of the Ni, weperformed x-ray absorption spectroscopy (XAS) and compared the measurements tosimulated XAS spectra based on multiplet ligand-field theory. Furthermore, Zndoping leads to much smaller effects on both the NMR spectra and thespin-lattice relaxation rates, indicating that Zn avoids occupying Cu sites.For magnetic Co impurities, $T_1^{-1}$ does not obey the gap like decrease, andthe low-temperature spectra get very broad. This could be related to theincrease of the Neel temperature which was observed by recent muSR andsusceptibility measurements, and is most likely an effect of the impurity spin$S\neq0$.

The effect of different in-chain impurities on the magnetic properties of the spin chain compound SrCuO$_2$ probed by NMR