Magnetic Dead Layers in La_0.7Sr_0.3MnO₃ Revisited

摘要

The magnetic dead layers in films a few nanometers thick are investigated for La_0.7Sr_0.3MnO₃ on SrTiO₃(STO), LaAlO₃(LAO), and (LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7 (LSAT) substrates. An anomalous moment found to persist above the Curie temperature of the La_0.7Sr_0.3MnO₃ films is not attributed to the films, but to oxygen vacancies at or near the surface of the substrate. The contribution to the moment from the substrate is as high as 20 μ_Bm2 in the case of STO or LSAT. The effect is increased by adding an STO cap layer. Taking this d-zero magnetism into account, extrapolated magnetic dead-layer thicknesses of 0.8, 1.5, and 3 nm are found for the manganite films grown on LSAT, STO, and LAO substrates, respectively. An STO cap layer eliminates the LSMO dead layer.