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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; Allieta, Mattia; Szabo, Dorothee Vinga; Schlabach, Sabine; Hagelstein, Michael; Ferrero, Claudio; Scavini, Marco

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 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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Verlagsausgabe §
DOI: 10.5445/IR/1000119424
Veröffentlicht am 18.05.2020
Cover der Publikation
Zugehörige Institution(en) am KIT Institut für Angewandte Materialien - Werkstoffkunde (IAM-WK)
Karlsruhe Nano Micro Facility (KNMF)
Institut für Beschleunigerphysik und Technologie (IBPT)
Publikationstyp Zeitschriftenaufsatz
Publikationsdatum 30.04.2020
Sprache Englisch
Identifikator ISSN: 2079-4991
KITopen-ID: 1000119424
HGF-Programm 49.02.01 (POF III, LK 01)
INT-KNMF Characterisation Lab
Erschienen in Nanomaterials
Band 10
Heft 5
Seiten 867
Vorab online veröffentlicht am 23.04.2020
Schlagwörter maghemite; pair distribution function; disordered magnetism; X-ray absorption spectroscopy; molecular dynamics; finite size effects
Nachgewiesen in Scopus
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