Tuning between the metallic antiferromagnetic and ferromagnetic phases of La1-xSrxMnO3 near x=0.5 by digital synthesis

We investigated cation-ordered La1-xSrxMnO3 about the half-doping level x similar to 0.5 in superlattices of alternating, single-unit-cell layers of LaMnO3 and SrMnO3. The effect of La/Sr cation order was addressed by comparing the structural, magnetic and transport properties of these superlattices with random-alloy films of equivalent composition. The samples were synthesized by ozone-assisted molecular-beam epitaxy onto SrTiO3 substrates. The superlattices could be tuned between ferromagnetic and antiferromagnetic metallic states by inserting extra single-unit-cell layers of LaMnO3 and SrMnO3, respectively. For x < 0.5, a ferromagnetic, metallic phase was observed. For x=0.50 and 0.55, A-type antiferromagnetic order was confirmed by neutron diffraction, with a Neel temperature of 300 K, significantly higher than bulk values. The enhanced Neel temperature was attributed to lattice strain rather than cation order.