Saturation magnetization values close to the bulk have been reported for coated magnetite nanoparticles with organic acids. The mechanism of this effect is not yet understood. Here, we show that a previously proposed rationalization in Nano Letters 12 (2021) 2499–2503 was based on electronic structure properties that are not consistent with several existing density functional theory studies. Our study is based on a wide set of Hubbard-corrected density-functional tight-binding (DTFB + U) and hybrid density functional theory (HSE06) calculations on Fe3O4 nanocubes of more than 400 atoms. We provide a new explanation for the spin ordering in coated nanoparticles, through the investigation of spin-flipping phenomena. In particular, we show that the spin-flip of d electrons at octahedral Fe3+ sites, which is confirmed to be more favorable near the surface, especially where atomic reorganization can take place such as at corner sites, can be hampered by the presence of adsorbed organic acids because they do not only limit the surface reconstruction but also allow for additional ferromagnetic superexchange interaction between octahedral Fe sites as a consequence of the carboxylates bridging binding mode. The proof-of-concept of this mechanism is given by a simplified model of the Fe(III) tert-butoxide dimer.

Bianchetti, E., Di Valentin, C. (2022). Mechanism of spin ordering in Fe3O4 nanoparticles by surface coating with organic acids. MATERIALS TODAY NANO, 17(March 2022) [10.1016/j.mtnano.2021.100169].

Mechanism of spin ordering in Fe3O4 nanoparticles by surface coating with organic acids

Bianchetti E.
Primo
;
Di Valentin C.
Ultimo
2022

Abstract

Saturation magnetization values close to the bulk have been reported for coated magnetite nanoparticles with organic acids. The mechanism of this effect is not yet understood. Here, we show that a previously proposed rationalization in Nano Letters 12 (2021) 2499–2503 was based on electronic structure properties that are not consistent with several existing density functional theory studies. Our study is based on a wide set of Hubbard-corrected density-functional tight-binding (DTFB + U) and hybrid density functional theory (HSE06) calculations on Fe3O4 nanocubes of more than 400 atoms. We provide a new explanation for the spin ordering in coated nanoparticles, through the investigation of spin-flipping phenomena. In particular, we show that the spin-flip of d electrons at octahedral Fe3+ sites, which is confirmed to be more favorable near the surface, especially where atomic reorganization can take place such as at corner sites, can be hampered by the presence of adsorbed organic acids because they do not only limit the surface reconstruction but also allow for additional ferromagnetic superexchange interaction between octahedral Fe sites as a consequence of the carboxylates bridging binding mode. The proof-of-concept of this mechanism is given by a simplified model of the Fe(III) tert-butoxide dimer.
Articolo in rivista - Articolo scientifico
Capping agents; Hybrid DFT; Magnetic properties; Magnetite; Saturation magnetization; Spin disorder;
English
Bianchetti, E., Di Valentin, C. (2022). Mechanism of spin ordering in Fe3O4 nanoparticles by surface coating with organic acids. MATERIALS TODAY NANO, 17(March 2022) [10.1016/j.mtnano.2021.100169].
Bianchetti, E; Di Valentin, C
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/354360
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