Effect of different in-chain impurities on the magnetic properties of the spin chain compound SrCuO2 probed by NMR
Effect of different in-chain impurities on the magnetic properties of the spin chain compound SrCuO2 probed by NMR
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NMR探测不同链内杂质对自旋链化合物SrCuO2磁性能的影响
DOI：
10.1103/physrevb.96.115135
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发表时间：
2017
影响因子：
3.7
通讯作者：
H. Grafe
中科院分区：
文献类型：
--
作者：
Y. Utz;F. Hammerath;R. Kraus;T. Ritschel;J. Geck;L. Hozoi;J. van den Brink;A. Mohan;C. Hess;K. Karmakar;S. Singh;D. Bounoua;R. Saint-Martin;L. Pinsard- Gaudart;A. Revcolevschi;B. Büchner;H. Grafe
用铜核磁共振方法研究了镍、钯、锌、钴不同掺杂量的海森伯自旋链化合物。仅用镍、钯、锌或钴取代少数铜离子对自旋链体系的磁性有很大影响。在Ni、Pd和Zn的情况下，低温核磁共振谱中异常的谱线展宽表明存在杂质诱导的局部交变磁化(LAM)，而向低温方向强烈衰减的自旋晶格弛豫速率表明自旋能隙的开放。在宽共振线内，能隙大小的分布由伸展的自旋晶格弛豫和变化所隐含。这些观测结果强烈地依赖于杂质浓度，因此可以用自旋反铁磁海森堡链的有限段模型来理解，即由于杂质引起的纯链分段。这对镍来说是令人惊讶的，因为它以前被认为是一种磁性杂质，它被邻近的铜自旋屏蔽。为了确定镍的状态，我们进行了X射线吸收光谱(XAS)测量，并与基于多重态配位场理论的模拟XAS光谱进行了比较。此外，锌掺杂对核磁共振谱和自旋晶格驰豫速率的影响都很小，表明锌避免了占据铜位。对于磁性钴杂质，不服从盖普利式下降，低温光谱变得很宽。这可能与Néel温度的升高有关，而且很可能是杂质自旋的影响。
TheHeisenberg spin chain compounddoped 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 theCu 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 ratestowards low temperatures indicate the opening of spin gaps. A distribution of gap magnitudes is implied by a stretched spin-lattice relaxation and a variation ofwithin 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 spinantiferromagnetic Heisenberg chain, i.e., pure chain segmentation due toimpurities. This is surprising for Ni as it was previously assumed to be a magnetic impurity withwhich is screened by the neighboring copper spins. In order to confirm thestate 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,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.