Line Narrowing in M?ssbauer Spectra of Superparamagnetic Fe3O4 Nanoparticles

22nd International Conference on Spectral Line Shapes

Hah, H.-Y.^1,2 ; Gray, S.^1,2 ; Johnson, C.E.^1 ; Johnson, J.A.^1,2 ; Kolesnichenko, V.^3 ; Kucheryavy, P.^3 ; Goloverda, G.^3

Center for Laser Applications, University of Tennessee, Space Institute, Tullahoma

TN

37388, United States^1

Department of Mechanical, Aerospace and Biomedical Engineering, University of Tennessee, Space Institute, Tullahoma

TN

37388, United States^2

Department of Chemistry, Xavier University, New Orleans

LA

70125, United States^3

关键词: Ensemble averages;    Fe3O4 nanoparticles;    High temperature;    Hyperfine splittings;    Line broadening;    Magnetic crystals;    Superparamagnetics;    Thermal fluctuations;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/548/1/012021/pdf
DOI  :  10.1088/1742-6596/548/1/012021

来源: IOP

【 摘 要 】

Nanoparticles of magnetic crystals below a critical size are single domain and exhibit superparamagnetism. If there are N atoms or molecules with magnetic moment μ in each particle, the magnetic moment of the particle is Nν. At high temperatures the thermal fluctuations of the magnetic moments give an ensemble average moment of zero and the Mössbauer spectrum is a single line. As the temperature, T, is lowered the fluctuations slow down and the sample acquires a magnetization and the Mossbauer line broadens and eventually shows magnetic hyperfine splitting. We have observed57Fe line broadening in nanoparticles of ferrimagnetic Fe3O4with diameters of 5.3 and 10.6 nm. The results have been analyzed using the motional narrowing equation familiar in nuclear magnetic resonance to determine the superparamagnetic fluctuation time and magnetic anisotropy.