Magnetic thermodynamics as proxy for chemical inhomogeneity in hemo-ilmenite solid solutions : A dynamic ac susceptibility study
Charilaou, M. ; Löffler, J. ; Gehring, A.
In: Physics and Chemistry of Minerals, 2012, vol. 39, no. 2, p. 87-92
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- In this study, we present ac susceptibility measurements for a synthetic and a natural hemo-ilmenite (HI) solid solution (x)FeTiO3-(1−x)Fe2O3 with compositions x=0.87(1) and 0.88(8), respectively. The focus of the investigation is the magnetic ordering at the Curie temperature T C and the spin-glass-like freezing at the freezing temperature T f. The sharpness of T C for the synthetic solid solution with well-defined structure indicates the chemical homogeneity of the solution, whereas the disperse magnetic ordering of the natural solid solution reveals inhomogeneities described as spin glass system ofvariations in composition x. The frequency dispersion of T f was determined between 10Hz and 10kHz and was found to obey a dynamic scaling power law. The relaxation rates deviate by five orders of magnitude where the synthetic solid solution exhibits ω0=3(1)×104Hz and the natural one 5.5×109Hz. The strong deviation is attributed to the difference in the ordered state above T f. These findings provide an insight into the cooling-rate effects of natural solid solutions and how magnetic thermodynamics can be used to probe the chemical homogeneity of such systems