Pure Nuclear Bragg Reflection due to Combined Magnetic and Quadrupole Interaction in Fe3O4

A pure nuclear Bragg reflection due to the combined magnetic and quadrupole interaction in the B-site Fe of Fe3O4 has been investigated. The 10 10 0 reflection (Bragg angle theta(B) = 46.48 degrees), which is electronically allowed for the A-site Fe but forbidden for the B-site Fe, was used to measure the reflection spectra. The measurements were conducted by a Fe-57 synchrotron Mossbauer diffractometer at SPring-8 BL11XU using a natural iron Fe3O4 single crystal. We have succeeded, for the first time, in observing the B-site emission spectrum due to the pure nuclear Bragg reflection in case an external magnetic field of 0.08 T was applied parallel to [(1) over bar 11] direction. On the other hand, in case an external magnetic field was applied parallel to [001] direction, the intensity of the B-site spectrum markedly decreased as a result of partial alignment of the magnetic moment in the [001] direction. Coexistence of the A- and B-site spectra results in the interference effect, such as broadening of the lines, asymmetric line shapes, and a slope of the base line. The analysis can be well conducted by using the Fano function. We found that the pure nuclear Bragg reflection gives sharper line shapes than the nuclear resonant scattering by the 45 degrees method.