Spin-lattice interaction in the insulator-to-metal transition of GdBaCo2O5+δ

We use electron paramagnetic resonance spectroscopy (EPR) and synchrotron radiation x-ray powder diffraction to study the temperature-induced insulator-to-metal transition (IMT) for GdBaCo2O5+δ samples in the δ range 0.54(1) δ 0.63(1). The EPR linewidth markedly changes across IMT and its temperature evolution can be explained considering spin state transition involving Co ions. The temperature dependences of the EPR linewidth and of the a lattice parameter fairly overlap each other suggesting spin-lattice interaction along the same crystallographic direction of the reported Ising-like spin anisotropy [A. A. Taskin et al., Phys. Rev. Lett. 90, 227201 (2003)]. A possible mechanism describing the interplay between this strong spin-lattice interaction and IMT is proposed.