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

We have studied the interface magnetism of La0.7Sr0.3MnO3 epitaxial thin fi lms deposited on MgO and SrTiO3 single crystal substrates by polarised neut ron reflectometry. Magnetisation measurements show that the magnetisation n ever reaches the full value of 3.7 mu(B)/atom expected for the 0.7/0.3 stoi chiometry. 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 magnetisat ion is clearly inhomogeneous through the thickness of the films and decreas es markedly when approaching the bottom and top interfaces of the film. A s tudy of the magnetisation profile variation as a function of temperature sh ows 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 observe d. (C) 2000 Published by Elsevier Science B.V. All rights reserved.