Magnetic properties of iron nitride-alumina nanocomposite materials prepared by high-energy ball milling |
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| Authors: | S R Mishra G J Long F Grandjean R P Hermann S Roy N Ali and A Viano |
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| Institution: | (1) Department of Physics, University of Memphis, Memphis, TN 38152, USA;(2) Department of Chemistry, University of Missouri-Rolla, Rolla, MO 65409-0010, USA;(3) Department of Physics, University of Liège, 4000 Sart-Tilman, Belgium;(4) Department of Physics, Southern Illinois University, Carbondale, IL 62901-4401, USA;(5) Department of Physics, Rhodes College, Memphis, TN 38112-1690, USA |
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| Abstract: | The structural and magnetic properties of the granular
iron nitride-alumina composite materials,
(FexN)0.2(Al2O3)0.8
and
(FexN)0.6(Al2O3)0.4,
fabricated using high-energy ball milling have been determined
by using X-ray diffraction, Mössbauer spectroscopy, and
magnetization measurements. The Mössbauer spectra, fit with a
distribution of hyperfine fields between zero and 40 T, indicate
that the weighted average field decreases with increasing
milling time. The isomer shift increases with milling time
because of a reduced iron 4s-electron density at the grain
boundaries. Coercive fields as high as 325 and 110 Oe are
obtained for
(FexN)0.2(Al2O3)0.8
at 5 and 300 K, respectively; the increase in the coercive field
upon cooling indicates the presence of superparamagnetic
particles. The coercive field increases with milling time
because of the reduced particle size. The decrease in the
magnetization results from the increase in both the
superparamagnetic fraction and the concentration of surface
defects with increased milling time. |
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| Keywords: | 75 50 Tt Fine-particle systems nanocrystalline
materials 81 20 Wk Machining milling 76 80 +y Mö ssbauer effect other gamma-ray
spectroscopy |
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