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Ni-impurity effect in high-$$T_c$$ cuprates studied by neutron scattering and XAFS spectroscopy

Hiraka, Haruhiro*; Wakimoto, Shuichi; Matsuda, Masaaki; Matsumura, Daiju; Nishihata, Yasuo; Mizuki, Junichiro; Yamada, Kazuyoshi*

Neutron scattering experiments using La$$_{2-x}$$Sr$$_{x}$$Cu$$_{1-y}$$Ni$$_{y}$$O$$_{4}$$ clarified that the parallel spin-density modulations (SDMs) in the superconducting phase are susceptible to Ni, in the same way as the diagonal SDMs in the insulating spin-glass phase. Ni substitution reduces the mobile hole concentration from $$x$$ down to $$x$$ - $$y$$. Polarized XAFS measurements using Ni $$K$$-edge probe two types of Ni valence states; Ni$$^{2+}$$ and Ni$$^{2+alpha}$$. It indicates that a strong hole localization occurs around Ni, resulting in an effective spin-$$frac{1}{2}$$ value at Ni sites. Therefore, a charge impurity nature of Ni is most likely realized when $$x$$ $$ge$$ $$y$$.



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Category:Chemistry, Multidisciplinary



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