Magnetic properties of pseudomorphic epitaxial films of Pr(0.7)Ca(0.3)MnO(3) under different biaxial tensile stresses

In order to analyze the effect of strain on the magnetic properties of narrow-band manganites, temperature-and field-dependent susceptibilities of about 8.5-nm-thick epitaxial Pr(0.7)Ca(0.3)MnO(3) films, respectively, grown on (001) and (110) SrTiO(3) substrates, have been compared. For ultrathin samples grown on (001) SrTiO(3), a bulklike cluster-glass magnetic behavior is found, indicative of the possible coexistence of antiferromagnetic and ferromagnetic phases. On the contrary, ultrathin films grown on (110) substrates show a robust ferromagnetism with a strong spontaneous magnetization of about 3.4 mu(B)/Mn atom along the easy axis. On the base of high-resolution reciprocal space mapping analyses performed by x-ray diffraction, the different behaviors are discussed in terms of the crystallographic constraints imposed by the epitaxy of Pr(0.7)Ca(0.3)MnO(3) on SrTiO(3). We suggest that for growth on (110) SrTiO(3), the tensile strain on the film c axis, lying within the substrate plane, favors the ferromagnetic phase, possibly by allowing a mixed occupancy and hybridization of both in-plane and out-of-plane e(g) orbitals. Our data allow to shed some physics of inhomogeneous states in manganites and on the nature of their ferromagnetic insulating state.