Effect of epitaxial strain on the exchange-bias properties of [La0.67Ca0.33MnO3/La0.33Ca0.67MnO3]15 multilayers: Resonant x-ray scattering measurements

Complementary x-ray synchrotron radiation diffraction (XRD) and resonant scattering (RXS) measurements were performed at the Mn K-edge between 10 and 300 K in order to analyze the effect of epitaxial strain and tetragonal lattice distortions on the exchange bias (EB) mechanism observed in [La2/3Ca1/3MnO3(FM)/La1/3Ca2/3MnO3(AF)]15 multilayers below a blocking temperature, TB, of 80 K. XRD measurements showed that the c/a axial ratio, an indication of the tetragonal lattice distortion in pseudocubic lattice settings, reaches its maximum at the onset of the EB effect and the corresponding structural correlation length varies substantially at the onset of TB. The in-plane lattice parameter a at TB is close to the bulk lattice parameters of the antiferromagnetic (AF) layers, thus indicating that the EB effect is related with the accommodation of strain inside the ferromagnetic (FM) and AF layers. RXS measurements revealed a ferrodistortive (FD) state. The RXS intensity difference signal exhibits a main-edge feature and a postedge feature at ∼6.57 keV that scales linearly with temperature and the c/a ratio up to 80 K. The disappearance of the postedge feature above 80 K(=TB) may signify a rearrangement of Mn-O-Mn bonding angles due to strain-driven effects at the FM/AF interfaces, inducing disorder in FD octahedral tilt ordering which may pin the local distortions below the TB