Mössbauer Study of the Magnetic Transition in ϵ-Fe2O3 Nanoparticles Using Synchrotron and Radionuclide Sources.

Nuclear γ-resonance experiments with energy and time resolved detection are carried out with ϵ-F₂O₃ nanoparticles and a ⁵⁷Co(Rh) laboratory Mössbauer source of γ radiation and a 14.4125 keV synchrotron radiation source on the ID18 beamline (ESRF) in the temperature range of 4–300 K. Both methods show a tremendous increase in the hyperfine field in tetrahedrally coordinated iron positions during the magnetic transition in the range of 80–150 K. As a result, the splitting of the quantum beat peaks in the nuclear scattering spectra is observed in the time interval of 20–170 ns with a periodicity of ∼ 30 ns. In addition, the first quantum beat is slightly shifted to shorter times. A correlation between the quadrupole shift and the orbital angular momentum of iron in ϵ-F₂O₃ nanoparticles is found. The magnetic transition leads to the rotation of the magnetic moment in the tetrahedral positions of iron around the axis of the electric field gradient by an angle of 44°. [ABSTRACT FROM AUTHOR]