Magnetoelastic coupling in RuSr2GdCu2O8

The complex Young's modulus, E, of RuSr2GdCu2O8 was measured for the first time in the temperature range from 1.5 up to 900 K. In the paramagnetic phase the real part of the Young's modulus decreases almost linearly with T, in agreement with the usual quasiharmonic approximation of the lattice dynamics described by the Debye model. A Debye temperature of about 390 K well reproduces the experimental data, in agreement with θD obtained by means of specific heat measurements performed by other authors. However, around the ferromagnetic transition the real part of E is affected by the onset of the magnetic order, slightly decreasing from the expected Debye behavior down to about 90 K, evidencing a magnetoelastic coupling in RuSr2GdCu2O8. On further cooling, E' increases, becoming greater than the value expected from the Debye model