Kuroda Shinji, Nishizawa Nozomi, Takita Kôki, Mitome Masanori, Bando Yoshio, Osuch Krzysztof, Dietl Tomasz
Institute of Materials Science, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8573, Japan.
Nat Mater. 2007 Jun;6(6):440-6. doi: 10.1038/nmat1910. Epub 2007 May 21.
The extensive experimental and computational search for multifunctional materials has resulted in the development of semiconductor and oxide systems, such as (Ga,Mn)N, (Zn,Cr)Te and HfO(2), which exhibit surprisingly stable ferromagnetic signatures despite having a small or nominally zero concentration of magnetic elements. Here, we show that the ferromagnetism of (Zn,Cr)Te, and the associated magnetooptical and magnetotransport functionalities, are dominated by the formation of Cr-rich (Zn,Cr)Te metallic nanocrystals embedded in the Cr-poor (Zn,Cr)Te matrix. Importantly, the formation of these nanocrystals can be controlled by manipulating the charge state of the Cr ions during the epitaxy. The findings provide insight into the origin of ferromagnetism in a broad range of semiconductors and oxides, and indicate possible functionalities of these composite systems. Furthermore, they demonstrate a bottom-up method for self-organized nanostructure fabrication that is applicable to any system in which the charge state of a constituent depends on the Fermi-level position in the host semiconductor.
对多功能材料进行的广泛实验和计算研究催生了半导体和氧化物体系的发展，例如（镓，锰）氮、（锌，铬）碲和氧化铪，尽管这些体系中磁性元素的浓度很低或名义上为零，但它们却呈现出惊人稳定的铁磁特征。在此，我们表明，（锌，铬）碲的铁磁性以及相关的磁光和磁输运功能，主要由嵌入贫铬（锌，铬）碲基体中的富铬（锌，铬）碲金属纳米晶体的形成所主导。重要的是，这些纳米晶体的形成可以通过在外延过程中操控铬离子的电荷态来控制。这些发现为深入了解广泛的半导体和氧化物中铁磁性的起源提供了思路，并指出了这些复合体系可能具备的功能。此外，它们展示了一种自下而上的自组织纳米结构制造方法，该方法适用于任何一种其组成部分的电荷态取决于主体半导体中费米能级位置的体系。
