Moessbauer study of spin structure transformation from an incommensurate to a commensurate state

We present crystallographic and magnetic properties of NiCr1.9857Fe0.02O4 by using X-ray diffractometry (XRD), vibrating sample magnetometry (VSM), and Moessbauer spectroscopy. The lattice constants a0 were determined to be 8.318 A. The ferrimagnetic Neel temperature (TN) for NiCr1.9857Fe0.02O4 is determined to be 90 K. The Moessbauer absorption spectra for all chromites at 4.2 K show two well developed sextets superposed with small difference of hyperfine fields (Hhf) caused by Cr3+ ions in two different magnetic sites. The values of the isomer shifts show that the charge states of Fe are Fe3+ for all temperature range. Ni-chromites Moessbauer spectra below TN present aline broadening due to a Jahn-Teller distortion and show that spin structure behavior of Cr ions change from an incommensurate to a commensurate state.