The temperature dependence of the magnetic hyperfine fields on 57 Fe nuclei at the tetrahedral (A) and octahedral (B) interstitial sites in (Zn, Cd, Cu) 0.5 Ni 0.5 Fe 2 O 4 oxides have been investigated in Mössbauer measurements at sample temperatures ranging from 79 K to 850 K. The samples were prepared by solid-state reaction, and their phase determined from XRD measurements, which also provided information on their X-ray densities, grain sizes and lattice constants. The magnetic transition temperatures between ordered and paramagnetic states were obtained from zero-velocity measurements. The Cu 0.5 Ni 0.5 Fe 2 O 4 sample is found to be antiferromagnetic with Néel temperature of 823 K, and its super-exchange interactions, J AB , J AA and J BB were determined to be j24.14 k B , j13.10 k B and +11.68 k B , respectively. The (Zn, Cd) 0.5 Ni 0.5 Fe 2 O 4 are ferrimagnetic with Curie points of 543 and 548 K, respectively, and corresponding average exchange integrals J o = 186 k B and 188 k B .

Radioactive 57 Mn isotopes have been implanted into Si 1jx Ge x crystals (x e 0.1) at elevated temperatures for Mössbauer studies of the diffusion of interstitial 57 Fe daughter atoms. The atomic jump frequency is found to increase upon Ge alloying. This is attributed to a lowering of the activation energy, i.e. the saddle point energy at hexagonal interstitial sites with Ge neighbour atoms.

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Ourinvestigations on substitutional and interstitial Fe in the group IV semiconductors, from 57 Fe Mössbauer measurements following 57 Mn implantation, have been continued with investigations in 3C-SiC. Mössbauer spectra were collected after implantation and measurement at temperatures from 300 to 905 K. Following

57 Fe Mössbauer spectroscopy, following the implantation of radioactive parent 57 Mn + ions, has been performed on two chemical vapour deposited diamond samples, one synthesized in 2003 (CVD03) and the other in 2005 (CVD05). The spectra of sample CVD05 were as observed previously in natural IIa diamonds: single lines corresponding to substitutional and interstitial Fe were superimposed on a broad quadrupole split doublet. The site fraction of Fe i reached 30% at 900 K. The spectra of the CVD03 sample showed, in addition to the above features, a strong contribution (>30%) from a quadrupole doublet attributable to the presence K. Bharuth-Ram · V. V. Naicker