Strong shape-dependence of Morin transition in α-Fe2O3 single-crystalline nanostructures

单人赛水晶的赤铁矿(-Fe2O3) nanorings (短 nanotubes ) 和 nanotubes 被一个热水的方法综合。高分辨率的传播电子显微镜学和精选区域的电子衍射证实 nanorings 和 nanotubes 的轴的方向与水晶的 c 轴平行。有趣地， Morin 转变与大约 115 nm 和大约 169 nm 的一条吝啬的外部直径的吝啬的试管长度在短 nanotubes 发生在大约 210 K。然而，它不与大约 317 nm 和大约 148 nm 的一条吝啬的外部直径的吝啬的试管长度发生在 nanotubes。磁化数据， X 光检查衍射模式，和房间温度 M 的详细分析 ? ssbauer 系列证明 Morin 转变的这很强壮的形状依赖对赤铁矿内在。我们向这吸引人的形状依赖份量上解释，以表面的相反的符号与 c 轴平行、垂直的表面飞机的磁性的 anisotropy 常数。

Single-crystalline hematite （α-Fe2O3） nanorings （short nanotubes） and nanotubes were synthesized by a hydrothermal method. High-resolution transmission electron microscopy and selected-area electron diffraction confirm that the axial directions of both the nanorings and nanotubes are parallel to the crystalline c-axis. Intriguingly, the Morin transition occurs at about 210 K in the short nanotubes with a mean tube length of about 115 nm and a mean outer diameter of about 169 nm. However, it does not occur in the nanotubes with a mean tube length of about 317 nm and a mean outer diameter of about 148 nm. Detailed analysis of magnetization data, X-ray diffraction patterns, and room-temperature M6ssbauer spectra demonstrates that this very strong shape-dependence of Morin transition is intrinsic to hematite. We explain this intriguing shape- dependence quantitatively, in terms of the opposite signs of the surface mag- netic anisotropy constants of the surface planes parallel and perpendicular to the c-axis.