Control of T_c in La_0.7Sr_0.3MnO₃ via piezostrain

Our results show a 10K shift of the magnetic Curie temperature for the ferromagnetic/ferroelectric heterostructure La_0.7Sr_0.3MnO₃/[Pb(Mg_1/3Nb_2/3)O₃]_0.68−[PbTiO₃]_0.32 (011). Two distinct polarization configurations can be set in the ferroelectric substrate and are stable at remanence; reciprocal space maps highlight the accompanying lattice parameter changes which impose a biaxial strain on the manganite thin film. The magnetic response to the strain changes is probed by temperature dependent Mn L_3,2 x-ray magnetic circular dichroism and resistance measurements. X-ray natural linear dichroism spectra for both strain states probe the valence charge anisotropy: The existing population imbalance between out-of-plane and in-plane oriented orbitals increases further with tensile strain, favoring orbital occupation in the surface plane. Multiplet and density functional theory calculations support the emerging picture that an increase in tensile in-plane strain leads to an increased energy difference between the two eg orbitals and a larger Mn-O-bond length. Increasing the electron-lattice coupling and reducing the eg electron itinerancy that leads to ferromagnetism due to double exchange coupling, results ultimately in lower T_C values.