MOSSBAUER RESONANCE OF FE57 IN OXIDIC SPINELS CONTAINING CU AND FE

The Mössbauer spectra of Fe57 in tetragonal and cubic CuFe2O4, CU0.5Zn0.5Fe2O4, and Cu0.3Cd0.3Fe2O4 have been investigated between 4.2-1000°K and in applied external magnetic fields. The spectra consist of a superposition of two apparent six-line patterns which are attributed predominantly to iron at the B sites (pattern I) and A sites (pattern II) of the crystal structure on the basis of their relative isomer shifts, hyperfine fields, quadrupole interactions, and thermal shifts. However, the intensity ratio of the Lorentzian fits of the two patterns does not correspond to the ratio of the Fe site occupancy factors as determined by diffraction methods. It is found that the patterns, especially I, are of a complex structure and exhibit anomalous line shapes due to various distributions of the neighboring cations and local Jahn-Teller type distortions of crystallographically equivalent sites. Both of these give rise to fluctuations in the A-B type super exchange interactions (resulting in varying hyperfine fields) and, to a lesser extent, to fluctuations in the quadrupole perturbation of the fields at the iron sites. The observed slight differences in the magnitude of the Heff(B) and the differential linewidths of II are interpreted in terms of a spin transfer from the A site cationic 3d spin moments to the 4S orbital of the B site Fe3+. By use of applied magnetic fields the separation of the patterns is increased so that the Lorentzian fits yield approximately correct intensity ratios. In cubic CuFe2O4 and in the spinels containing Zn and Cd, the site distortions are such that patterns I and II cannot be resolved in the zero applied field spectra whereas this is possible if external fields are employed. © 1968.