Substrate orientation dependent characteristics of half-metallic and metallic superlattices [La0. 7Sr0. 3MnO3/LaNiO3] 10

Abstract

We report a detailed study on the orientation dependent growth characteristics, electronic structure, transport, magnetic, and vibrational excitations in atomically flat interfaces of [La0.7Sr0.3MnO3/LaNiO3]10 superlattices (SLs) coherently grown on (001/011/111)-SrTiO3 substrates by the pulsed laser deposition technique. X-ray reflectometry confirms the periodic superlattice stacks from the Kiessig interference fringes and well-defined even interfaces between the nickelate and manganite layers. A complex local atomic environment across the interfaces was noticed, yet trivalent La, divalent Sr, and mixed valent Ni2+/3+ and Mn3+/4+ electronic states prevail at the core level with enhanced relative intensity ratio of the Mn ions in the superlattices grown on (111) oriented SrTiO3 substrates as compared to those grown on (001) and (011) oriented SrTiO3. The temperature (5≤T≤300K) dependence of electrical resistivity 𝜌(𝑇) analysis reveals 3D variable range hopping model [𝜌(T)=𝜌0exp(T0/T)(1/4)] with large magnitude of hopping energies (≥40 meV) for the SL-111 system associated with the high energy gap developed by the accumulation of disorderness in the individual constituents of polar layers. Moreover, all SL systems exhibit reduced ferromagnetic ordering temperatures (67≤T𝐶≤110K) with a low-temperature anomaly (11.4≤T∗≤22K) and a substantial enhancement in the effective exchange interaction (J𝑒𝑓𝑓∼3.52meV) having altered ground state-spin configuration S∼1/2 different from S=3/2 of La0.75Sr0.25MnO3. Nevertheless, the SL-011 system exhibits large anisotropy field H𝐾∼18kOe and cubic anisotropy constant K1∼9.3×103J/m3 in comparison to the other two orientations. The second order two-phonon interaction driven by the local polaronic distortion causes significant changes in the vibrational excitations of the investigated system. Nonetheless, most of the Raman modes follow the substrate-induced, highly oriented epitaxial growth pattern except for two modes 𝜈4 (326cm−1) and 𝜈8 (728cm−1), which slightly differ in the case of SL-111 superlattices.