Influence of substrate in all-ferromagnetic superlattices

The Raman scattering and magnetization of the superlattices consisting of ultrathin layer of two metal-like ferromagnets La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) grown on (001)-oriented LaAlO3(LAO) and SrTiO3(STO) substrates, were studied. The Raman spectrum of LAO/[1-u.c. LSMO/2-u.c. SRO]x60 superlattice shows modes which are shifted towards higher frequencies relative to that of LAO/[2-u.c. SRO/1-u.c. LSMO]x60 superlattice. However, the Raman spectra of these superlattices indicate the presence of orthorhombic structures of LSMO and SRO for both stacking orders. The STO/[1-u.c. LSMO/2-u.c. SRO]x60 superlattices exhibit Curie temperature (TC) at ~270 K and Neel temperature (TN) at ~140 K. Surprisingly, TC of superlattice on LAO grown simultaneously with STO reduces to ~209 K for in-plane magnetic field and to ~99 K for out-plane field. But for the reverse stacking grown on LAO the TC increases to ~121 and ~218 K for in-plane and out-of-plane orientation of field, respectively. The superlattices grown on LAO do not show any signature of TN. Our result clearly indicates the influence of substrate induced stress and stacking order on exchange coupling between the LSMO and SRO in the superlattices, providing a useful tool towards tailoring the magnetic properties of heterostructures.