Surface structure controlling nanoparticle behavior

Magnetism of ferrihydrite, magnetite, and maghemite

Tjisse Hiemstra*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

14 Citations (Scopus)

Abstract

Iron oxide nanoparticles are omnipresent in nature and of great importance for environmental sciences and technology. The size-dependent magnetic behavior of ferrihydrite (Fh), magnetite (Fe3O4), and maghemite (γ-Fe2O3) has been studied in relation to the surface structure. The selected minerals have in common the presence of tetrahedral Fe. This Fe polyhedron is unstable at the surface when forming singly coordinated ligand(s). This leads to the size-dependency of the polyhedral composition, which is for Fh in excellent agreement with the relative contributions of edge and corner sharing measured with high-energy total X-ray scattering. For Fh, superparamagnetic behavior scales with particle volume in which magnetic coupling is proportional to a fraction of the Fe per particle. Magnetic saturation at low temperature scales with size and is predominantly due to polyhedral surface depletion. The mineral core of Fh may behave ferrimagnetically as well as antiferromagnetically. Both have opposite particle size dependency, for which a surface structural model has been developed. The relative stability of ferrimagnetic and antiferromagnetic Fh is related to a slight difference in the surface Gibbs free energy (∼0.03 J m-2). At the same surface structure, the predicted crossover point is at ∼4 nm, above which the core of Fh shifts from antiferromagnetic to ferrimagnetic. For magnetite and maghemite, the size dependency of the ferrimagnetic behavior can be described with the same model as that developed for Fh by only adjusting the maximum magnetic saturation of the ideal bulk material to its theoretical value. As discussed and quantified, the structural defects of superparamagnetic Fe-oxide nanoparticles (SPION) will lower the magnetic saturation at a given size.
Original languageEnglish
Pages (from-to)752-764
JournalEnvironmental Science: Nano
Volume5
Issue number3
DOIs
Publication statusPublished - 1 Jan 2018

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Ferrosoferric Oxide
maghemite
ferrihydrite
Magnetism
Magnetite
Surface structure
magnetite
Saturation magnetization
Nanoparticles
Minerals
Temperature scales
Magnetic couplings
saturation
Gibbs free energy
X ray scattering
Iron oxides
Particle size
Ligands
environmental technology
Defects

Cite this

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title = "Surface structure controlling nanoparticle behavior: Magnetism of ferrihydrite, magnetite, and maghemite",
abstract = "Iron oxide nanoparticles are omnipresent in nature and of great importance for environmental sciences and technology. The size-dependent magnetic behavior of ferrihydrite (Fh), magnetite (Fe3O4), and maghemite (γ-Fe2O3) has been studied in relation to the surface structure. The selected minerals have in common the presence of tetrahedral Fe. This Fe polyhedron is unstable at the surface when forming singly coordinated ligand(s). This leads to the size-dependency of the polyhedral composition, which is for Fh in excellent agreement with the relative contributions of edge and corner sharing measured with high-energy total X-ray scattering. For Fh, superparamagnetic behavior scales with particle volume in which magnetic coupling is proportional to a fraction of the Fe per particle. Magnetic saturation at low temperature scales with size and is predominantly due to polyhedral surface depletion. The mineral core of Fh may behave ferrimagnetically as well as antiferromagnetically. Both have opposite particle size dependency, for which a surface structural model has been developed. The relative stability of ferrimagnetic and antiferromagnetic Fh is related to a slight difference in the surface Gibbs free energy (∼0.03 J m-2). At the same surface structure, the predicted crossover point is at ∼4 nm, above which the core of Fh shifts from antiferromagnetic to ferrimagnetic. For magnetite and maghemite, the size dependency of the ferrimagnetic behavior can be described with the same model as that developed for Fh by only adjusting the maximum magnetic saturation of the ideal bulk material to its theoretical value. As discussed and quantified, the structural defects of superparamagnetic Fe-oxide nanoparticles (SPION) will lower the magnetic saturation at a given size.",
author = "Tjisse Hiemstra",
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Surface structure controlling nanoparticle behavior : Magnetism of ferrihydrite, magnetite, and maghemite. / Hiemstra, Tjisse.

In: Environmental Science: Nano, Vol. 5, No. 3, 01.01.2018, p. 752-764.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Surface structure controlling nanoparticle behavior

T2 - Magnetism of ferrihydrite, magnetite, and maghemite

AU - Hiemstra, Tjisse

PY - 2018/1/1

Y1 - 2018/1/1

N2 - Iron oxide nanoparticles are omnipresent in nature and of great importance for environmental sciences and technology. The size-dependent magnetic behavior of ferrihydrite (Fh), magnetite (Fe3O4), and maghemite (γ-Fe2O3) has been studied in relation to the surface structure. The selected minerals have in common the presence of tetrahedral Fe. This Fe polyhedron is unstable at the surface when forming singly coordinated ligand(s). This leads to the size-dependency of the polyhedral composition, which is for Fh in excellent agreement with the relative contributions of edge and corner sharing measured with high-energy total X-ray scattering. For Fh, superparamagnetic behavior scales with particle volume in which magnetic coupling is proportional to a fraction of the Fe per particle. Magnetic saturation at low temperature scales with size and is predominantly due to polyhedral surface depletion. The mineral core of Fh may behave ferrimagnetically as well as antiferromagnetically. Both have opposite particle size dependency, for which a surface structural model has been developed. The relative stability of ferrimagnetic and antiferromagnetic Fh is related to a slight difference in the surface Gibbs free energy (∼0.03 J m-2). At the same surface structure, the predicted crossover point is at ∼4 nm, above which the core of Fh shifts from antiferromagnetic to ferrimagnetic. For magnetite and maghemite, the size dependency of the ferrimagnetic behavior can be described with the same model as that developed for Fh by only adjusting the maximum magnetic saturation of the ideal bulk material to its theoretical value. As discussed and quantified, the structural defects of superparamagnetic Fe-oxide nanoparticles (SPION) will lower the magnetic saturation at a given size.

AB - Iron oxide nanoparticles are omnipresent in nature and of great importance for environmental sciences and technology. The size-dependent magnetic behavior of ferrihydrite (Fh), magnetite (Fe3O4), and maghemite (γ-Fe2O3) has been studied in relation to the surface structure. The selected minerals have in common the presence of tetrahedral Fe. This Fe polyhedron is unstable at the surface when forming singly coordinated ligand(s). This leads to the size-dependency of the polyhedral composition, which is for Fh in excellent agreement with the relative contributions of edge and corner sharing measured with high-energy total X-ray scattering. For Fh, superparamagnetic behavior scales with particle volume in which magnetic coupling is proportional to a fraction of the Fe per particle. Magnetic saturation at low temperature scales with size and is predominantly due to polyhedral surface depletion. The mineral core of Fh may behave ferrimagnetically as well as antiferromagnetically. Both have opposite particle size dependency, for which a surface structural model has been developed. The relative stability of ferrimagnetic and antiferromagnetic Fh is related to a slight difference in the surface Gibbs free energy (∼0.03 J m-2). At the same surface structure, the predicted crossover point is at ∼4 nm, above which the core of Fh shifts from antiferromagnetic to ferrimagnetic. For magnetite and maghemite, the size dependency of the ferrimagnetic behavior can be described with the same model as that developed for Fh by only adjusting the maximum magnetic saturation of the ideal bulk material to its theoretical value. As discussed and quantified, the structural defects of superparamagnetic Fe-oxide nanoparticles (SPION) will lower the magnetic saturation at a given size.

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DO - 10.1039/c7en01060e

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VL - 5

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JO - Environmental Science: Nano covers the benefits...

JF - Environmental Science: Nano covers the benefits...

SN - 2051-8153

IS - 3

ER -