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Structure and magnetic properties of rf thermally plasma synthesized Mn and Mn–Zn ferrite nanoparticles

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3 Author(s)
Son, S. ; Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 ; Swaminathan, R. ; McHenry, M.E.

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Plasma synthesis has previously been shown to be a viable route to producing nanocrystalline magnetite and Ni ferrite nanoparticles. In this work nanocrystalline powders of Mn and Mn–Zn ferrites have been synthesized using a 50 kW–3 MHz rf (radio frequency) induction plasma torch. We investigate these materials for soft magnetic applications. High-energy ball milled Mn + Fe powders and (Mn+Zn) +Fe powders (≪10 μm) in the stoichiometric ratio of 1:2 were used as precursors for the ferrite synthesis. Compressed air was used in the oxygen source for oxidation of metal species in the plasma. X-ray diffraction patterns for the plasma-torched Mn ferrite and MnZn ferrite powders were indexed to the spinel ferrite crystal structure. An average grain size of ∼20 nm was determined from Scherrer analysis confirmed by transmission electron microscopy studies. The particles also exhibited faceted polygonal growth forms with the associated truncated cuboctahedral shapes. Room-temperature vibrating sample magnetometer measurements of the hysteretic response revealed saturation magnetization Ms and coercivity Hc of Mn ferrite are 23.65 emu/g and 20 Oe, respectively. The Néel temperatures of Mn ferrite powders before and after annealing (500 °C, 30 min) were determined to be 200 and 360 °C, respectively. Inductively coupled plasma chemical analysis and energy dispersive x-ray analysis data on the plasma-torched powders indicated deviations in the Mn or Zn contents than the ideal stoichiometry. MnZn ferrite was observed to have a Néel temperature increased by almost 400 °C as compared with as-synthesized Mn ferrite but with a larger coercivity of ∼35 Oe. © 2003 American Institute of Physics.

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Journal of Applied Physics  (Volume:93 ,  Issue: 10 )