Elastic strain control of electronic structure, and magnetic properties of [Pr_(1-x)Ca_xMnO_3/SrTiO_3]_(15) superlattices

摘要

We report the growth, electronic structure, and in-plane magnetic properties of pulsed laser deposition grown 2D superlattice structures [Pr_(0.7)Ca_(0.3)MnO_3/SrTiO_3]_(15) and [Pr_(0.5)Ca_(0.5)MnO_3/SrTiO_3]_(15) on (001) oriented SrTiO_3 and LaAlO_3 single crystal substrates. The x-ray reflectivity measurements reveal well-defined interfaces between the manganite and titanate layers along with the existence of Kiessig fringes, providing the evidence for the smooth periodic superlattice structure. The reciprocal space mapping provides signature of tetragonal distortion in all the superlattices. The electronic structure determined from the x-ray photoelectron spectroscopy reveals divalent Sr and Ca, tetravalent Ti, and mixed valent Mn with a pronounce shift of binding energy peaks toward the higher energy side in the superlattices grown on (001) oriented LaAlO_3 as compared to those grown on SrTiO_3. These superlattices exhibit highly anisotropic ferromagnetic character. We used the law of approach to saturation to determine the anisotropy field (H_K) and cubic anisotropy constant (K_1) for all the investigated superlattices. This analysis yields the highest H_K～9kOe and K_1～ 8× 10~5 erg/cc for the [Pr_(0.7)Ca_(0.3)MnO_3/SrTiO_3]_(15) superlattice system. Furthermore, significant enhancement of the overall magnetic moment and a decrease in T_C (＜100 K) was observed in the case of LaAlO_3 grown superlattice, which indicates a substantial role of residual elastic strain on the magnetic ordering. Our results indicate that the strain induced elongation of MnO_6 octahedra leads to finite possibility of non-orthogonal overlapping of orbitals in the presence of large crystal field splitting of e_g levels, which, in turn, causes suppression of the ferromagnetic double exchange interaction.