Influence of substrate in all-ferromagnetic superlattices

The Raman scattering and magnetization of the superlattices consisting of ultrathin layer of two metal-like ferromagnets La<inf>0.7</inf>Sr<inf>0.3</inf>MnO<inf>3</inf> (LSMO) and SrRuO<inf>3</inf> (SRO) grown on (001)-oriented LaAlO<inf>3</inf>(LAO) and SrTiO<inf>3</inf>(STO) substrates, were studied. The Raman spectrum of LAO/[1-u.c. LSMO/2-u.c. SRO]<inf>x60</inf> superlattice shows modes which are shifted towards higher frequencies relative to that of LAO/[2-u.c. SRO/1-u.c. LSMO]<inf>x60</inf> 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]<inf>x60</inf> superlattices exhibit Curie temperature (T<inf>C</inf>) at ∼270 K and Neel temperature (TN) at ∼140 K. Surprisingly, T<inf>C</inf> 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 T<inf>C</inf> 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 T<inf>N</inf>. 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.