We present novel low-frequency (0.1 Hz–50 Hz) measurements of the complex elastic susceptibility of KMn 1 − x Ca x F 3 ( x = 0, 0.003, 0.018). An ultraslow relaxational process in pure KMnF 3 just below T c = 186 K is discovered and explained by a refined heat diffusion model. In addition, a giant softening (superelasticity) due to domain wall motion is found. In contrast to the case of SrTiO 3 and also of pure KMnF 3 , we find a ferroelastic domain freezing in the mixed crystals with 0.3% Ca substitution. The dispersion displays a Cole-Davidson–like behaviour with an additional logarithmic low-frequency contribution in agreement with the theoretical results for weak pinning of elastic interfaces in crystals with randomly distributed impurities.
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Schranz et al. (2003) studied this question.
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