Interface magnetism of La0.7Sr0.3MnO3 thin films studied by neutron reflectometry

We have studied the interface magnetism of La0.7Sr0.3MnO3 epitaxial thin films deposited on MgO and SrTiO3 single crystal substrates by polarised neutron reflectometry. Magnetisation measurements show that the magnetisation never reaches the full value of 3.7 mu(B)/atom expected for the 0.7/0.3 stoichiometry. Although the coercivity of the films is rather low (H-c < 10 mT), the magnetic saturation value is reached only for fields larger than 200 mT. By polarised neutron reflectometry we have observed that the magnetisation is clearly inhomogeneous through the thickness of the films and decreases markedly when approaching the bottom and top interfaces of the film. A study of the magnetisation profile variation as a function of temperature shows that a thin top layer of 3-5 nm is greatly perturbed. The magnetisation is also reduced on a rather large depth into the core of the film where a depression of 15-20% from the substrate to the top interface can be observed. (C) 2000 Published by Elsevier Science B.V. All rights reserved.