Strain effect on magnetic properties of La0.7Ca0.3MnO3/SrRuO3 superlattices

Coherent interfaces between magnetic oxides such as La0.7Sr0.3MnO3 and SrRuO3 may induce an intense magnetic coupling. Recent work indicated an impact of elastic strain on the strength and even the sign of the coupling. Superlattices (SL) of La0.7Ca0.3MnO3/SrRuO3 with layer thicknesses below 10 unit cells were grown by pulse laser deposition simultaneously on SrTiO3(001) (STO), LaAlO3(001) (LAO) and piezoelectric 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (001) (PMN-PT) substrates and structurally characterized by X-ray diffraction (XRD). On LAO, the SL assumes a compressive strain state, i. e. the lattice parameter is larger out-of-plane than in-plane, whereas on PMN-PT it shows a tensile strain state and on STO an intermediate strain value. Magnetization measurements demonstrate a strong antiferromagnetic (AFM) coupling in SLs on STO and LAO substrates which is due to superexchange interaction between Ru and Mn ions. The AFM coupling seems to decrease under tensile strain. The coupling is much weaker on PMN-PT, probably because of higher interface roughness. In order to probe the effect of elastic strain directly, magnetization loops in reversibly controlled strain states have been recorded for SLs on PMN-PT.