Spin Structure Change in Co-Substituted BiFeO3

The spin structure in BiFe1-xCoxO3 (x = 0.05, 0.10, 0.15, 0.20) was investigated as a function of Co substitution, temperature, and magnetic field. It was found that the cycloidal spin structure of BiFeO3 changed to a collinear one with spin canting and composition-independent spontaneous magnetization of similar to 0.25 mu B/f.u. for the Co substituted samples on heating. The collinear phase was stabilized under magnetic fields. The spin structure change was clarified also by the temperature dependence of Fe-57 Mossbauer spectra, and the results indicated the first order nature of this transition.