In-plane anisotropy in the magnetic and transport properties of manganite ultrathin films

To analyze the conducting and magnetic properties near the film and substrate interface in manganites, ultrathin films (thickness≤1000.3em0ex) of La0.7Sr0.3MnO₃ were epitaxially grown by molecular-beam epitaxy on single-crystal (001) LaAlO₃, (110) NdGaO₃, and (001) SrTiO₃ substrates. Structural, magnetic, and magnetoresistive properties were investigated. All samples exhibit a substrate-independent decrease of the c-lattice parameter for thinnest films. Highly anisotropic behavior in both transport and magnetic properties were measured along the in-plane directions parallel to the substrate crystallographic axes. In particular, for the thinnest films (600.3em0ex), the negative magnetoresistance at about 1200.3em0exK with the average current along one of the crystallographic directions, is larger than the room-temperature colossal value. In the same low-temperature range, with the current along the other in-plane crystallographic direction, the magnetoresistance changes sign (resulting to be magnetic field independent for T~1500.3em0exK). Such an in-plane anisotropy of transport and magnetic properties is investigated with respect to possible intrinsic and extrinsic physical mechanisms.