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.

Local structure and magnetism of Fe2O3 maghemite nanocrystals: The role of crystal dimension / M. Coduri, P. Masala, L.D. Bianco, F. Spizzo, D. Ceresoli, C. Castellano, S. Cappelli, C. Oliva, S. Checchia, M. Allieta, D.-. Szabo, S. Schlabach, M. Hagelstein, C. Ferrero, M. Scavini. - In: NANOMATERIALS. - ISSN 2079-4991. - 10:5(2020 Apr 30). [10.3390/nano10050867]

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

M. Coduri
Primo
;
P. Masala
Secondo
;
C. Castellano;S. Cappelli;C. Oliva;S. Checchia;M. Allieta;M. Scavini
Ultimo
2020

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.
Disordered magnetism; Finite size effects; Maghemite; Molecular dynamics; Pair distribution function; X-ray absorption spectroscopy
Settore CHIM/02 - Chimica Fisica
Settore CHIM/03 - Chimica Generale e Inorganica
Settore FIS/01 - Fisica Sperimentale
Settore FIS/03 - Fisica della Materia
30-apr-2020
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/742658
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