The $S=1/2$ Heisenberg spin chain compound ${\mathrm{SrCuO}}_2$ doped with different amounts of nickel (Ni), palladium (Pd), zinc (Zn), and cobalt (Co) has been studied by means of Cu nuclear magnetic resonance (NMR). Replacing only a few of the $S=1/2$ Cu ions with Ni, Pd, Zn, or Co has a major impact on the magnetic properties of the spin chain system. In the case of Ni, Pd, and Zn an unusual line broadening in the low temperature NMR spectra reveals the existence of an impurity-induced local alternating magnetization (LAM), while strongly decaying spin-lattice relaxation rates $T_1^{-1}$ towards low temperatures indicate the opening of spin gaps. A distribution of gap magnitudes is implied by a stretched spin-lattice relaxation and a variation of $T_1^{-1}$ within the broad resonance lines. These observations depend strongly on the impurity concentration and therefore can be understood using the model of finite segments of the spin $1/2$ antiferromagnetic Heisenberg chain, i.e., pure chain segmentation due to $S=0$ impurities. This is surprising for Ni as it was previously assumed to be a magnetic impurity with $S=1$ which is screened by the neighboring copper spins. In order to confirm the $S=0$ state of the Ni, we performed x-ray absorption spectroscopy (XAS) and compared the measurements to simulated XAS spectra based on multiplet ligand-field theory. Furthermore, Zn doping leads to much smaller effects on both the NMR spectra and the spin-lattice relaxation rates, indicating that Zn avoids occupying Cu sites. For magnetic Co impurities, $T_1^{-1}$ does not obey the gaplike decrease, and the low-temperature spectra get very broad. This could be related to an increase of the Néel temperature and is most likely an effect of the impurity spin $S\ne 0$.

中文翻译：

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核磁共振研究链内不同杂质对自旋链化合物SrCuO2磁性的影响

这 $\mathrm{小号}=\mathrm{1个}/\mathrm{2个}$ 海森堡自旋链化合物 ${\mathrm{氧化铜}}_{\mathrm{2个}}$通过铜核磁共振（NMR）研究了掺杂不同量的镍（Ni），钯（Pd），锌（Zn）和钴（Co）的掺杂。仅更换少数几个$\mathrm{小号}=\mathrm{1个}/\mathrm{2个}$具有Ni，Pd，Zn或Co的Cu离子对自旋链系统的磁性能有重大影响。在Ni，Pd和Zn的情况下，低温NMR谱图中的异常线展宽表明存在杂质诱导的局部交变磁化（LAM），而自旋晶格弛豫速率却大大降低${Ť}_{\mathrm{1个}}^{-\mathrm{1个}}$趋于低温表明自旋间隙的打开。拉伸自旋晶格弛豫和${Ť}_{\mathrm{1个}}^{-\mathrm{1个}}$在广泛的共鸣线之内。这些观察结果在很大程度上取决于杂质浓度，因此可以使用自旋的有限段模型来理解$\mathrm{1个}/\mathrm{2个}$ 反铁磁海森堡链，即由于 $\mathrm{小号}=0$杂质。对于Ni来说，这是令人惊讶的，因为以前认为它是一种磁性杂质，$\mathrm{小号}=\mathrm{1个}$被相邻的铜旋转屏蔽。为了确认$\mathrm{小号}=0$在Ni的状态下，我们进行了X射线吸收光谱（XAS），并将测量结果与基于多重配体场理论的模拟XAS光谱进行了比较。此外，Zn掺杂对NMR光谱和自旋晶格弛豫速率的影响都小得多，这表明Zn避免占据Cu位。对于磁性Co杂质，${Ť}_{\mathrm{1个}}^{-\mathrm{1个}}$不遵循间隙的减少，并且低温光谱变得非常宽。这可能与Néel温度的升高有关，并且很可能是杂质自旋的影响$\mathrm{小号}\ne 0$。