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Local structure and magnetism of Fe2O3 maghemite nanocrystals : The role of crystal dimension

Coduri, Mauro ; Masala, Paolo ; Bianco, Lucia Del ; Spizzo, Federico ; Ceresoli, Davide ; Castellano, Carlo ; Cappelli, Serena ; Oliva, Cesare ; Checchia, Stefano LU and Allieta, Mattia , et al. (2020) In Nanomaterials 10(5).
Abstract

Here we report on the impact of reducing the crystalline size on the structural and magnetic properties of γ-Fe2O3 maghemite nanoparticles. A set of polycrystalline specimens with crystallite size ranging from ~2 to ~50 nm was obtained combining microwave plasma synthesis and commercial samples. Crystallite size was derived by electron microscopy and synchrotron powder diffraction, which was used also to investigate the crystallographic structure. The local atomic structure was inquired combining pair distribution function (PDF) and X-ray absorption spectroscopy (XAS). PDF revealed that reducing the crystal dimension induces the depletion of the amount of Fe tetrahedral sites. XAS confirmed significant bond... (More)

Here we report on the impact of reducing the crystalline size on the structural and magnetic properties of γ-Fe2O3 maghemite nanoparticles. A set of polycrystalline specimens with crystallite size ranging from ~2 to ~50 nm was obtained combining microwave plasma synthesis and commercial samples. Crystallite size was derived by electron microscopy and synchrotron powder diffraction, which was used also to investigate the crystallographic structure. The local atomic structure was inquired combining pair distribution function (PDF) and X-ray absorption spectroscopy (XAS). PDF revealed that reducing the crystal dimension induces the depletion of the amount of Fe tetrahedral sites. XAS confirmed significant bond distance expansion and a loose Fe-Fe connectivity between octahedral and tetrahedral sites. Molecular dynamics revealed important surface effects, whose implementation in PDF reproduces the first shells of experimental curves. The structural disorder affects the magnetic properties more and more with decreasing the nanoparticle size. In particular, the saturation magnetization reduces, revealing a spin canting effect. Moreover, a large effective magnetic anisotropy is measured at low temperature together with an exchange bias effect, a behavior that we related to the existence of a highly disordered glassy magnetic phase.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Disordered magnetism, Finite size effects, Maghemite, Molecular dynamics, Pair distribution function, X-ray absorption spectroscopy
in
Nanomaterials
volume
10
issue
5
article number
867
publisher
Multidisciplinary Digital Publishing Institute (MDPI)
external identifiers
  • scopus:85085044880
  • pmid:32365930
ISSN
2079-4991
DOI
10.3390/nano10050867
language
English
LU publication?
yes
id
2ddce65d-185c-4320-b169-0d67ae20a7db
date added to LUP
2020-06-17 16:16:53
date last changed
2021-03-03 03:44:49
@article{2ddce65d-185c-4320-b169-0d67ae20a7db,
  abstract     = {<p>Here we report on the impact of reducing the crystalline size on the structural and magnetic properties of γ-Fe<sub>2</sub>O<sub>3</sub> maghemite nanoparticles. A set of polycrystalline specimens with crystallite size ranging from ~2 to ~50 nm was obtained combining microwave plasma synthesis and commercial samples. Crystallite size was derived by electron microscopy and synchrotron powder diffraction, which was used also to investigate the crystallographic structure. The local atomic structure was inquired combining pair distribution function (PDF) and X-ray absorption spectroscopy (XAS). PDF revealed that reducing the crystal dimension induces the depletion of the amount of Fe tetrahedral sites. XAS confirmed significant bond distance expansion and a loose Fe-Fe connectivity between octahedral and tetrahedral sites. Molecular dynamics revealed important surface effects, whose implementation in PDF reproduces the first shells of experimental curves. The structural disorder affects the magnetic properties more and more with decreasing the nanoparticle size. In particular, the saturation magnetization reduces, revealing a spin canting effect. Moreover, a large effective magnetic anisotropy is measured at low temperature together with an exchange bias effect, a behavior that we related to the existence of a highly disordered glassy magnetic phase.</p>},
  author       = {Coduri, Mauro and Masala, Paolo and Bianco, Lucia Del and Spizzo, Federico and Ceresoli, Davide and Castellano, Carlo and Cappelli, Serena and Oliva, Cesare and Checchia, Stefano and Allieta, Mattia and Szabo, Dorothee Vinga and Schlabach, Sabine and Hagelstein, Michael and Ferrero, Claudio and Scavini, Marco},
  issn         = {2079-4991},
  language     = {eng},
  month        = {04},
  number       = {5},
  publisher    = {Multidisciplinary Digital Publishing Institute (MDPI)},
  series       = {Nanomaterials},
  title        = {Local structure and magnetism of Fe<sub>2</sub>O<sub>3</sub> maghemite nanocrystals : The role of crystal dimension},
  url          = {http://dx.doi.org/10.3390/nano10050867},
  doi          = {10.3390/nano10050867},
  volume       = {10},
  year         = {2020},
}