Antiferromagnetic interaction between paramagnetic Co ions in the diluted magnetic semiconductor Zn 1-x Co x O
Antiferromagnetic interaction between paramagnetic Co ions in the diluted magnetic semiconductor Zn 1-x Co x O
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DOI：
10.1103/physrevb.81.075204
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发表时间：
2010-01
影响因子：
3.7
通讯作者：
Masaaki Kobayashi;Y. Ishida;J. I. Hwang;Y. Osafune;A. Fujimori;Y. Takeda;T. Okane;Yuichi Saitoh;Keisuke Kobayashi;H. Saeki;Tsuyoshi Kawai;Hitoshi Tabata
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作者：
Masaaki Kobayashi;Y. Ishida;J. I. Hwang;Y. Osafune;A. Fujimori;Y. Takeda;T. Okane;Yuichi Saitoh;Keisuke Kobayashi;H. Saeki;Tsuyoshi Kawai;Hitoshi Tabata
利用x射线磁圆二色性（XMCD）研究了在氧化锌（0001）衬底上随氧压变化的同外延生长的${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$ （$x=0.07$和0.10）薄膜在$\text{Co}\text{2p$核心能级吸收边的磁性。所有薄膜的吸收谱线形状相同，表明${\text{Co}}^{2+}$离子取代了Zn位。XMCD强度对磁场和温度的依赖关系与磁化测量结果一致，表明除了Co之外没有其他磁矩源，并证明了在同外延${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$薄膜中存在顺磁性和铁磁性成分共存。与以往研究的异质外延${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$薄膜的铁磁性形成对比。利用居里-魏斯定律对XMCD强度的分析揭示了顺磁性Co离子之间存在反铁磁相互作用。缺失的XMCD强度和磁化信号表明，大多数Co离子是非磁性的，这可能是因为它们彼此之间存在强反铁磁耦合。在高真空中退火可以降低顺磁信号和铁磁信号。我们将还原归因于Co离子与反铁磁纳米团簇在${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$中的热扩散和聚集。
The magnetic properties of ${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$ ($x=0.07$ and 0.10) thin films, which were homoepitaxially grown on a ZnO(0001) substrates with varying relatively high oxygen pressure, have been investigated using x-ray magnetic circular dichroism (XMCD) at $\text{Co}\text{ }2p$ core-level absorption edge. The line shapes of the absorption spectra are the same in all the films and indicate that the ${\text{Co}}^{2+}$ ions substitute for the Zn sites. The magnetic-field and temperature dependences of the XMCD intensity are consistent with the magnetization measurements, indicating that except for Co there are no additional sources for the magnetic moment, and demonstrate the coexistence of paramagnetic and ferromagnetic components in the homoepitaxial ${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$ thin films, in contrast to the ferromagnetism in the heteroepitaxial ${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$ films studied previously. The analysis of the XMCD intensities using the Curie-Weiss law reveals the presence of antiferromagnetic interaction between the paramagnetic Co ions. Missing XMCD intensities and magnetization signals indicate that most of Co ions are nonmagnetic probably because they are strongly coupled antiferromagnetically with each other. Annealing in a high vacuum reduces both the paramagnetic and ferromagnetic signals. We attribute the reductions to thermal diffusion and aggregation of Co ions with antiferromagnetic nanoclusters in ${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$.