Magnetic properties of ultra-small goethite nanoparticles

Erik Brok, Cathrine Frandsen, Daniel Esmarch Madsen, H. Jacobsen, J. O. Birk, K. Lefmann, J. Bendix, K. S. Pedersen, C. B. Boothroyd, A. A. Berhe, G. G. Simeoni, Steen Mørup

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Goethite (α-FeOOH) is a common nanocrystalline antiferromagnetic mineral. However, it is typically difficult to study the properties of isolated single-crystalline goethite nanoparticles, because goethite has a strong tendency to form particles of aggregated nanograins often with low-angle grain boundaries. This nanocrystallinity leads to complex magnetic properties that are dominated by magnetic fluctuations in interacting grains. Here we present a study of the magnetic properties of 5.7 nm particles of goethite by use of magnetization measurements, inelastic neutron scattering and Mo¨ssbauer spectroscopy. The `ultra-small' size of these particles (i.e. that the particles consist of one or only a few grains) allows for more direct elucidation of the particles' intrinsic magnetic properties. We find from ac and dc magnetization measurements a significant upturn of the magnetization at very low temperatures most likely due to freezing of spins in canted spin structures. From hysteresis curves we estimate the saturation magnetization from uncompensated magnetic moments to be σs = 0.044 A m2 kg-1 at room temperature. Inelastic neutron scattering measurements show a strong signal from excitations of the uniform mode (q = 0 spin waves) at temperatures of 100-250 K and Mössbauer spectroscopy studies show that the magnetic fluctuations are dominated by `classical' superparamagnetic relaxation at temperatures above ~170 K. From the temperature dependence of the hyperfine fields and the excitation energy of the uniform mode we estimate a magnetic anisotropy constant of around 1.0 × 105 J m-3.
Original languageEnglish
JournalJournal of Physics D: Applied Physics
Volume47
Issue number36
Pages (from-to)365003
Number of pages13
ISSN0022-3727
DOIs
Publication statusPublished - 2014

Cite this

Brok, Erik ; Frandsen, Cathrine ; Madsen, Daniel Esmarch ; Jacobsen, H. ; Birk, J. O. ; Lefmann, K. ; Bendix, J. ; Pedersen, K. S. ; Boothroyd, C. B. ; Berhe, A. A. ; Simeoni, G. G. ; Mørup, Steen. / Magnetic properties of ultra-small goethite nanoparticles. In: Journal of Physics D: Applied Physics. 2014 ; Vol. 47, No. 36. pp. 365003.
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title = "Magnetic properties of ultra-small goethite nanoparticles",
abstract = "Goethite (α-FeOOH) is a common nanocrystalline antiferromagnetic mineral. However, it is typically difficult to study the properties of isolated single-crystalline goethite nanoparticles, because goethite has a strong tendency to form particles of aggregated nanograins often with low-angle grain boundaries. This nanocrystallinity leads to complex magnetic properties that are dominated by magnetic fluctuations in interacting grains. Here we present a study of the magnetic properties of 5.7 nm particles of goethite by use of magnetization measurements, inelastic neutron scattering and Mo¨ssbauer spectroscopy. The `ultra-small' size of these particles (i.e. that the particles consist of one or only a few grains) allows for more direct elucidation of the particles' intrinsic magnetic properties. We find from ac and dc magnetization measurements a significant upturn of the magnetization at very low temperatures most likely due to freezing of spins in canted spin structures. From hysteresis curves we estimate the saturation magnetization from uncompensated magnetic moments to be σs = 0.044 A m2 kg-1 at room temperature. Inelastic neutron scattering measurements show a strong signal from excitations of the uniform mode (q = 0 spin waves) at temperatures of 100-250 K and M{\"o}ssbauer spectroscopy studies show that the magnetic fluctuations are dominated by `classical' superparamagnetic relaxation at temperatures above ~170 K. From the temperature dependence of the hyperfine fields and the excitation energy of the uniform mode we estimate a magnetic anisotropy constant of around 1.0 × 105 J m-3.",
author = "Erik Brok and Cathrine Frandsen and Madsen, {Daniel Esmarch} and H. Jacobsen and Birk, {J. O.} and K. Lefmann and J. Bendix and Pedersen, {K. S.} and Boothroyd, {C. B.} and Berhe, {A. A.} and Simeoni, {G. G.} and Steen M{\o}rup",
year = "2014",
doi = "10.1088/0022-3727/47/36/365003",
language = "English",
volume = "47",
pages = "365003",
journal = "Journal of Physics D: Applied Physics",
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Brok, E, Frandsen, C, Madsen, DE, Jacobsen, H, Birk, JO, Lefmann, K, Bendix, J, Pedersen, KS, Boothroyd, CB, Berhe, AA, Simeoni, GG & Mørup, S 2014, 'Magnetic properties of ultra-small goethite nanoparticles', Journal of Physics D: Applied Physics, vol. 47, no. 36, pp. 365003. https://doi.org/10.1088/0022-3727/47/36/365003

Magnetic properties of ultra-small goethite nanoparticles. / Brok, Erik; Frandsen, Cathrine; Madsen, Daniel Esmarch; Jacobsen, H.; Birk, J. O.; Lefmann, K.; Bendix, J.; Pedersen, K. S.; Boothroyd, C. B.; Berhe, A. A.; Simeoni, G. G.; Mørup, Steen.

In: Journal of Physics D: Applied Physics, Vol. 47, No. 36, 2014, p. 365003.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Magnetic properties of ultra-small goethite nanoparticles

AU - Brok, Erik

AU - Frandsen, Cathrine

AU - Madsen, Daniel Esmarch

AU - Jacobsen, H.

AU - Birk, J. O.

AU - Lefmann, K.

AU - Bendix, J.

AU - Pedersen, K. S.

AU - Boothroyd, C. B.

AU - Berhe, A. A.

AU - Simeoni, G. G.

AU - Mørup, Steen

PY - 2014

Y1 - 2014

N2 - Goethite (α-FeOOH) is a common nanocrystalline antiferromagnetic mineral. However, it is typically difficult to study the properties of isolated single-crystalline goethite nanoparticles, because goethite has a strong tendency to form particles of aggregated nanograins often with low-angle grain boundaries. This nanocrystallinity leads to complex magnetic properties that are dominated by magnetic fluctuations in interacting grains. Here we present a study of the magnetic properties of 5.7 nm particles of goethite by use of magnetization measurements, inelastic neutron scattering and Mo¨ssbauer spectroscopy. The `ultra-small' size of these particles (i.e. that the particles consist of one or only a few grains) allows for more direct elucidation of the particles' intrinsic magnetic properties. We find from ac and dc magnetization measurements a significant upturn of the magnetization at very low temperatures most likely due to freezing of spins in canted spin structures. From hysteresis curves we estimate the saturation magnetization from uncompensated magnetic moments to be σs = 0.044 A m2 kg-1 at room temperature. Inelastic neutron scattering measurements show a strong signal from excitations of the uniform mode (q = 0 spin waves) at temperatures of 100-250 K and Mössbauer spectroscopy studies show that the magnetic fluctuations are dominated by `classical' superparamagnetic relaxation at temperatures above ~170 K. From the temperature dependence of the hyperfine fields and the excitation energy of the uniform mode we estimate a magnetic anisotropy constant of around 1.0 × 105 J m-3.

AB - Goethite (α-FeOOH) is a common nanocrystalline antiferromagnetic mineral. However, it is typically difficult to study the properties of isolated single-crystalline goethite nanoparticles, because goethite has a strong tendency to form particles of aggregated nanograins often with low-angle grain boundaries. This nanocrystallinity leads to complex magnetic properties that are dominated by magnetic fluctuations in interacting grains. Here we present a study of the magnetic properties of 5.7 nm particles of goethite by use of magnetization measurements, inelastic neutron scattering and Mo¨ssbauer spectroscopy. The `ultra-small' size of these particles (i.e. that the particles consist of one or only a few grains) allows for more direct elucidation of the particles' intrinsic magnetic properties. We find from ac and dc magnetization measurements a significant upturn of the magnetization at very low temperatures most likely due to freezing of spins in canted spin structures. From hysteresis curves we estimate the saturation magnetization from uncompensated magnetic moments to be σs = 0.044 A m2 kg-1 at room temperature. Inelastic neutron scattering measurements show a strong signal from excitations of the uniform mode (q = 0 spin waves) at temperatures of 100-250 K and Mössbauer spectroscopy studies show that the magnetic fluctuations are dominated by `classical' superparamagnetic relaxation at temperatures above ~170 K. From the temperature dependence of the hyperfine fields and the excitation energy of the uniform mode we estimate a magnetic anisotropy constant of around 1.0 × 105 J m-3.

U2 - 10.1088/0022-3727/47/36/365003

DO - 10.1088/0022-3727/47/36/365003

M3 - Journal article

VL - 47

SP - 365003

JO - Journal of Physics D: Applied Physics

JF - Journal of Physics D: Applied Physics

SN - 0022-3727

IS - 36

ER -