Magnetoelastic coupling in A2FeReO6 (A = Ba and Ca) probed by elastic constants and magnetostriction measurements

Double perovskites A2FeReO6 (A = Ba, Ca) have been synthesized and studied using a combination of resonant ultrasound spectroscopy, magnetization, and magnetostriction measurements. A large softening in C44 over a wide temperature range is observed for Ba2FeReO6 below its Curie temperature (TC ≈ 311 K), which is indicative of a structural distortion. This softening is partially suppressed upon application of a low magnetic field. For Ca2FeReO6, both the longitudinal and shear moduli show a softening starting at T ≈ 160 K. In addition, magnetoelastic coupling constants have been estimated from elastic constants and magnetostriction data, which provide direct evidence of pronounced coupling between magnetism and the lattice degrees of freedom present in both compounds.