Spin-lattice coupling in multiferroic Pb(Fe1/2Nb1/2)O3 thin films

We made magnetization and x-ray diffraction measurements on an epitaxial $\text{Pb}\left({\text{Fe}}_{1/2}{\text{Nb}}_{1/2}\right){\text{O}}_3$ 200 nm film. From the temperature dependence of the out-of-plane lattice parameter, we can assign a Burns’ temperature at $T_d\sim 640\text{K}$ , a temperature at $T^{\ast }\sim 510\text{K}$ (related to the appearance of static polar nanoregions), and an anomaly occurring at 200 K. The latter is precisely the Néel temperature $T_N$ determined from magnetization and points to spin-lattice coupling at $T_N\sim 200\text{K}$ . We also observe “weak ferromagnetism” up to 300 K and propose superantiferromagnetic clusters as a plausible scenario to explain this hysteresis above $T_N$ .