Magnetic anisotropy and core-shell structure origin of the biogenic ferrihydrite nanoparticles

• Published in: Journal of alloys and compounds Vol. 851; p. 156753
• Main Authors: Knyazev, Yu.V., Balaev, D.A., Stolyar, S.V., Bayukov, O.A., Yaroslavtsev, R.N., Ladygina, V.P., Velikanov, D.A., Iskhakov, R.S.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15-01-2021; Elsevier BV
• Subjects: Antiferromagnetism; Atoms & subatomic particles; Core-shell nanoparticles; Core-shell structure; Crystallization; Ferrihydrite; Ferrimagnetism; Iron; Magnetic anisotropy; Magnetic measurement; Magnetic moments; Magnetic properties; Magnetism; Mossbauer spectroscopy; Nanoparticles; Particle size distribution; Structural models; Superparamagnetism; Surface magnetic anisotropy; Core-shell nanoparticles; Ferrihydrite; Superparamagnetism; Surface magnetic anisotropy
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2020.156753

Ferrihydrite is a low-crystalline nanoscale matter. The uncompensated magnetic moment of the ferrihydrite caused by the antiferromagnetic ordering of the magnetic moments of iron atoms and leads to the magnetic properties very similar to those of ferro- and ferrimagnetic nanoparticles. In this study, we investigated the biogenic ferrihydrite nanoparticles with the narrow size distribution and an average diameter of ≈2 nm obtained by the bacteria life cycle. The features caused by the surface effects and the inhomogeneous structure of ferrihydrite have been examined in the temperature range of 4–300 K using Mössbauer spectroscopy and magnetometry. Based on the Mössbauer data, we identified the superparamagnetic blocking temperature at the temperature of 30 K for the largest ferryhidrite particles. We established that the exceptional magnetic anisotropy of ferrihydrite (KV=1.2⋅105 erg/cm3 and KS=0.1 erg/cm2) is reached because of the highly developed ferrihydrite nanoparticles’ surface. According to the Mössbauer data, we propose a core-shell structural model of the biogenic ferrihydrite particles. We found that the size of the dense core depends on the particle size. The well-crystallized core is formed only for nanoparticles larger than ≈2 nm, whereas smaller particles consist entirely of a matter with a lower density of iron atoms.
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•We discuss the core-shell structure of the biogenic ferrihydrite nanoparticles using Mössbauer spectroscopy and magnetometry in the temperature range of 4–300 K.•We found that the size of the dense core depends on the nanoparticle size. The particles less than ≈2 nm have no dense core.•It was shown that the surface magnetic anisotropy originates from the inhomogeneous structure of the ferrihydrite particles