Magnetite/hematite core/shell fibres grown by laser floating zone method

Abstract

Magnetite (Fe3O4) is a very important material due to its unique physical and chemical properties. However, the low redox stability and tendency towards oxidation impose certain limitations on the conditions, where Fe3O4 can be successfully used. A possibility to control and prevent oxidation of Fe3O4 thus represents an important challenge for materials engineering. In the present work, the laser floating zone (LFZ) method was employed to produce Fe3O4 fibres using hematite (Fe2O3) as a precursor material. Different growth conditions, namely pulling rate in the range 10-400 mm/h, were studied. The prepared fibres showed a core/shell structure, where the core is isolated by a shell of Fe2O3. The pulling rate was found to be a crucial growth parameter to control the crystalline nature of the fibres, particularly, the thickness of the shell. Increasing the pulling rate favours the formation Fe2O3 phase and, thus, decreases the width of shell isolating phase. X-ray diffraction (XRD) analysis was performed to identify the presence of Fe3O4 and Fe2O3 phases. The morphology and phase distribution of the grown fibres were analyzed by optical microscopy. Electrical properties of the fibres were measured at various temperatures, to understand the influence of pulling rate on the fibres shell. Vibrating sample magnetometer (VSM) measurements were used to study the dc magnetic susceptibility and hysteresis curves behaviour of Fe3O4 phase in the temperature range 5-300 K. (C) 2013 Elsevier B.V. All rights reserved.