Anomalous Elastic Properties of Fe₂TiO₄

Abstract

The temperature dependence of elastic constants c 11 – c 12 and c 44 of Fe 2.05 Ti 0.95 O 4.00 is measured by the ultrasonic pulse echo method, using a small (110) platelet with approximate dimension of 5×7×1.364mm, for the temperature range of 77°∼300°K. c 11 – c 12 decreases anomalously with decreasing temperature in the paramagnetic phase, whereas c 44 increases. An extraordinarily large attenuation is observed around the Curie temperature in the 1\bar10 shear mode which couples to c 11 – c 12 . The elastic constants obtained, c 11 - c 12 =0.265×10 12 dyne/cm 2 and c 44 =0.396×10 12 dyne/cm 2 at room temperature, are almost an order of magnitude smaller than those of magnetite and spinel, and provide a reasonable explanation for the giant magnetostriction observed in the crystal. The soft mode in the crystal is interpreted to be due to the Jahn-Teller relaxation effect of Fe 2+ ions in the tetrahedral site.