Thermally activated processes and superparamagnetism in Bi12MnO20 nanoparticles: A comparative study

• Published in: Journal of magnetism and magnetic materials Vol. 401; pp. 890 - 896
• Main Authors: de Oliveira, L.A.S., Pentón-Madrigal, A., Guimarães, A.P., Sinnecker, J.P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2016
• Subjects: Fine-particle systems; Relaxation effect; Temperature-hysteresis effect; Fine-particle systems; Relaxation effect; Temperature-hysteresis effect
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2015.11.013

Manganese sillenite (Bi12MnO20) nanoparticles having average particle size between 22 and 43nm were synthesized by a low temperature soft chemical route under refluxing conditions. A careful structural and microstructural characterization by means of high resolution X-ray diffraction experiments and transmission electron microscopy is presented. The as-cast powder displayed an isotropic superparamagnetic (SPM) behavior with a blocked state for temperatures below TB∼13.0K. We used three different measurement techniques to extract and compare the Bi12MnO20 blocking temperatures. First, we extracted TB with the modified Bean–Livingstone model from the coercive field temperature dependence obtained from hysteresis curves measured as a function of temperature. Then, the blocking temperature distribution function, f(TB), was obtained by deriving the zero field-cooled/field-cooled curves difference. For each applied field, the maximum of the distribution function gave us the mean blocking temperature value. Finally, the maximum of the magnetic susceptibility imaginary part as a function of frequency was used, combined with the Néel–Brown equation, to extract the blocking temperature. All measurement techniques yield an equivalent dependence of TB with H of the Bi12MnO20 superparamagnetic nanoparticles.