Hasuike N, Nishio K, Katoh H, Suzuki A, Isshiki T, Kisoda K, Harima H
Department of Electronics, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
J Phys Condens Matter. 2009 Feb 11;21(6):064215. doi: 10.1088/0953-8984/21/6/064215. Epub 2009 Jan 20.
Zn(1-x)Co(x)O samples were prepared by a standard solid-state reaction method. Zn(1-x)Co(x)O crystals in the wurtzite structure were obtained with a Co composition of up to 22.1%. The a- and c-axis lengths increased and decreased, respectively, with an increase in Co composition. Raman spectra showed systematic broadening of the E(2) (high) phonon mode associated with the increase in Co composition, and electronic transitions of Co in the oxygen tetrahedron were observed in optical absorption measurement. These results indicated systematic substitution of Co into the Zn sites. Furthermore, an additional broad absorption band at 2.4-3.3 eV corresponding to the charge transfer (CT) process [Formula: see text] was also observed. The Raman spectra showed strong enhancement of the LO phonon due to a resonant Raman process induced with the coupling of the LO phonon and a photo-excited carriers mediated CT gap. These results suggest the possibility of carrier-induced ferromagnetism based on double exchange interaction in Zn(1-x)Co(x)O by visible light irradiation.
采用标准固态反应法制备了Zn(1-x)Co(x)O样品。获得了纤锌矿结构的Zn(1-x)Co(x)O晶体，其中Co的组成高达22.1%。随着Co组成的增加，a轴和c轴长度分别增加和减小。拉曼光谱显示，与Co组成增加相关的E(2)（高）声子模式出现系统性展宽，并且在光吸收测量中观察到了Co在氧四面体中的电子跃迁。这些结果表明Co系统地替代了Zn位点。此外，还观察到一个对应于电荷转移（CT）过程[公式：见原文]的2.4 - 3.3 eV的额外宽吸收带。由于LO声子与光激发载流子介导的CT能隙耦合诱导的共振拉曼过程，拉曼光谱显示LO声子有强烈增强。这些结果表明，通过可见光照射，基于双交换相互作用，Zn(1-x)Co(x)O中存在载流子诱导铁磁性的可能性。
