Mossbauer Study of the Magnetic Transition in epsilon-Fe2O3 Nanoparticles Using Synchrotron and Radionuclide Sources

 Nuclear gamma-resonance experiments with energy and time resolved detection are carried out with epsilon-F2O3 nanoparticles and a Co-57(Rh) laboratory Mossbauer source of gamma 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 similar to 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 epsilon-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 degrees.