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Nano Research

Article Title

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

Keywords

hematite nanostructures, Morin transition, shape-dependence, surface magnetic anisotropy

Abstract

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 Mössbauer spectra demonstrates that this very strong shape-dependence of Morin transition is intrinsic to hematite. We explain this intriguing shapedependence quantitatively, in terms of the opposite signs of the surface magnetic anisotropy constants of the surface planes parallel and perpendicular to the c-axis.

Graphical Abstract

Publisher

Tsinghua University Press

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