Magnetic properties of synthetic six-line ferrihydrite nanoparticles

Yohan Guyodo, Subir K. Banerjee, R. Lee Penn, David Burleson, Thelma S. Berquo, Takele Seda, Peter Solheid

Research output: Contribution to journalArticlepeer-review

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Abstract

Three synthetic samples of six-line ferrihydrite (Fh5.4, Fh4.1, and Fh3.0), with average particle sizes of 5.4, 4.1, and 3.0 nm (respectively), have been studied by low-temperature magnetic techniques, Mössbauer spectroscopy, transmission electron microscopy, and X-ray absorption spectroscopy. Magnetic data indicate that these nanoparticles are not only antiferromagnetic, but that they also possess a ferromagnetic-like moment due to the presence of uncompensated spins. Both magnetic and Mössbauer data indicate that nanoparticles of six-line ferrihydrite are superparamagnetic at room temperature, with a low-temperature transition between blocked and unblocked magnetic states dependent on average particle size. In particular, low-field magnetic susceptibility data display a peak in amplitude at 45 K (Fh3.0), 55 K (Fh4.1), and 80 K (Fh5.4). Low-temperature induced magnetization data, acquired in magnetic fields up to 5 T, also display clearly a superparamagnetic behavior. These data were tentatively modeled as the sum of two contributions: a linear term due to the antiferromagnetic susceptibility and a nonlinear term due to the uncompensated spins. Model estimates of the magnetization carried by the uncompensated spins (Mnc) show a decrease in Mnc with increasing temperature. Extrapolation of Mnc values down to zero provided an estimate of the Néel temperature for six-line ferrihydrite on the order of 500 K.

Original languageEnglish (US)
Pages (from-to)222-233
Number of pages12
JournalPhysics of the Earth and Planetary Interiors
Volume154
Issue number3-4
DOIs
StatePublished - Mar 16 2006

Bibliographical note

Funding Information:
Portions of this work were performed at GeoSoilEnviroCARS (Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation (NSF)—Earth Sciences (EAR-0217473), Department of Energy—Geosciences (DE-FG02-94ER14466), and the State of Illinois. Use of the APS was supported by the U.S. Department of Energy, Basic Energy Sciences, Office of Energy Research, under Contract No. W-31-109-Eng-38. We greatly acknowledge help from Matt Newville at the APS. Funding of this research was provided by NSF grant No. EAR-0311869, by the Biogeosciences program of the Earth Sciences division. We acknowledge useful reviews from A. Hirt and A. Kosterov, and comments from the guest editor A. Muxworthy. IRM contribution No. 0411. LSCE contribution No. 1369.

Keywords

  • EXAFS
  • Ferrihydrite
  • Magnetic properties
  • Mössbauer effect
  • Rock magnetism

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