Dear folks,
I have synthesized Fe nano particle samples using an ambient condition.
Based on an ESR measurement at room temperature, large sized (~50 nm) NPs showed less magnetic strength than smaller ones (1~3 nm), which sounds the opposite case of the conventional theory. Can defects or aggregation of clusters during the enlargement process of NPs lead the magnetic loss?
What would be the reasonable clues/references behind this unusual case?
With Best Regards,
Get pure nanoparticles Fe difficult. Their composition may include oxides, carbides ... You get alpha iron, gamma iron? Small additions of Fe can significantly alter the magnetic properties of the iron ore powder. See our works.
Regards.
First, I agree with Yuri about possible impurities producing different magnetic material. Secondly, generally the extent of magnetisation depends on the size of the Weiss domains. I don't know how large they are for Fe, but given that they are small, a 50 nm particle may contain several domains, while smaller can contain only one. The magnetisation of the latter will be far larger.
Agreeing with both previous comments, I would add that ESR at room temperature might not be the best technique to assess the magnetization of nanoparticles. First, if available, you should go to T < 10 K approx. to block the superparamagnetism. And I would perform direct magnetization Mvs H curves or Mossbauer spectroscopy (which, in addition to magnetic hyperfine field will give you the fingerprints of each possible iron-containning phase.
Hope this helps.
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