Shape- and field-dependent Morin transitions in structured α-Fe₂O₃

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• 作者：Subarna Mitra ; Soumen Das ; Soumen Basu ; Puspendu Sahu ; Kalyan M ; al
• 关键词：α ; -Fe₂O₃ ; Solvothermal ; Morin transition
• 刊名：Journal of Magnetism and Magnetic Materials
• 出版年：2009
• 出版时间：September 2009
• 年：2009
• 卷：321
• 期：18
• 页码：2925-2931
• 全文大小：636 K

文摘

We report shape- and field-dependent magnetic properties of ellipsoid-, spindle-, flattened- and rhombohedra-shaped α-Fe₂O₃ samples prepared by solvothermal technique. We observed that a magnetic spin-flip mechanism, mostly known as Morin transition (T_M), depends on the shape of α-Fe₂O₃ as well as on the applied magnetic field. In each of these structures the obtained value of T_M was less than its bulk value of 263 K. We observed that T_M shifted from highest 251.4 K for ellipsoid to lowest 220.8 K for rhombohedra structure, with intermediate values of T_M for the other two structures. However, for rhombohedra structure T_M shifted from 220.8 to 177.5 K under the external magnetic field of 100 Oe–30 kOe, respectively. The observed lowering of T_M in the structured sample was analyzed in terms of elementary size, shape of the nanocrystallites, lattice parameters and occupancy of Fe⁺³ ions as well. These parameters were determined from the Rietveld refinement process using MAUD software.