Magnetic properties of heat treated bacterial ferrihydrite nanoparticles

• Published in: Journal of magnetism and magnetic materials Vol. 410; pp. 171 - 180
• Main Authors: Balaev, D.A., Krasikov, A.A., Dubrovskiy, A.A., Popkov, S.I., Stolyar, S.V., Bayukov, O.A., Iskhakov, R.S., Ladygina, V.P., Yaroslavtsev, R.N.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-07-2016
• Subjects: Ferrihydrite; Nanoparticles; Superparamagnetism; Nanoparticles; Ferrihydrite; Superparamagnetism
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2016.02.059

The magnetic properties of ferrihydrite nanoparticles, which are products of vital functions of Klebsiella oxitoca bacteria, have been studied. The initial powder containing the nanoparticles in an organic shell was subjected to low-temperature (T=160°C) heat treatment for up to 240h. The bacterial ferrihydrite particles exhibit a superparamagnetic behavior. Their characteristic blocking temperature increases from 26 to 80K with the heat treatment. Analysis of the magnetization curves with regard to the magnetic moment distribution function and antiferromagnetic contribution shows that the low-temperature heat treatment enhances the average magnetic moment of a particle; i.e., the nanoparticles coarsen, probably due to their partial agglomeration during heat treatment. It was established that the blocking temperature nonlinearly depends on the particle volume. Therefore, a model was proposed that takes into account both the bulk and surface magnetic anisotropy. Using this model, the bulk and surface magnetic anisotropy constants KV≈1.7×105erg/cm3 and KS≈0.055erg/cm2 have been determined. The effect of the surface magnetic anisotropy of ferrihydrite nanoparticles on the observed magnetic hysteresis loops is discussed.
•Ferrihydrite nanoparticles of biogenic origin are obtained.•Magnetic characterization reveals superparamagnetic behavior.•The blocking temperature increases upon the low-temperature (T=160°C) heat treatment.•The blocking temperature nonlinearly depends on the particle volume.•The bulk and surface magnetic anisotropy constants have been determined.