We report on the growth of epitaxial bilayers of the La 2/3 Sr 1/3 MnO 3 ͑LSMO͒ half-metallic ferromagnet and the BiFeO 3 ͑BFO͒ multiferroic, on SrTiO 3 ͑001͒ by pulsed laser deposition. The growth mode of both layers is two dimensional, which results in unit-cell smooth surfaces. We show that both materials keep their properties inside the heterostructures, i.e., the LSMO layer ͑11 nm thick͒ is ferromagnetic with a Curie temperature of ϳ330 K, while the BFO films shows ferroelectricity down to very low thicknesses ͑5 nm͒. Conductive-tip atomic force microscope mappings of BFO/LSMO bilayers for different BFO thicknesses reveal a high and homogeneous resistive state for the BFO film that can thus be used as a ferroelectric tunnel barrier in tunnel junctions based on a half-metal. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2170432͔To a great extent, today's research in spintronics focuses on the development of materials and devices concepts.1 In many cases, the former are requisites to the latter. Recently, several families of materials have been developed in this sense, a typical example being that of diluted magnetic semiconductors.2 As spintronics effects rely on the spin polarization of the electrical current, materials with large, ideally total, spin-polarization have also been extensively investigated. With these so-called half-metals, 3 a considerable increase in the tunnel magnetoresistance of magnetic tunnel junctions 4 has indeed been achieved, at least at low temperatures.
5Another emerging family of magnetic materials are multiferroics. 6 In these compounds, several ferroic orders ͑e.g., magnetic and electric͒ coexist, with some coupling between them ͑the magnetoelectric effect͒. 7 Most are ferroelectric and antiferromagnetic, a notable exception being BiMnO 3 that is ferromagnetic. 8 A propotypical multiferroic that has attracted a lot of attention lately is BiFeO 3 ͑BFO͒.9,10 It is a ferroelectric and weakly ferromagnetic rhombohedral perovskite with order temperatures far above room temperature ͑T C = 1043 K,
11T N = 647 K͒.12 BFO thus crystallizes in the same structure as several known half-metallic ferromagnets ͑such as La 2/3 Sr 1/3 MnO 3 ,La 2/3 Ca 1/3 MnO 3 , or Sr 2 FeMoO 6 ͒, which makes it possible to combine it with these materials in multifunctional epitaxial heterostructures. Several promising types of devices can be imagined from this combination, as discussed, for instance, by Binek et al. 13,14 In particular, one can think of using very thin layers of BiFeO 3 as multiferroic tunnel barriers. If ferroelectric, these layers should have the same functionalities as those of recently developed 15 and modeled 16,17 ferroelectric tunnel barriers, combined with a magnetic ordering and a possible magnetoelectric coupling.In this letter, we describe the growth and properties of bilayers of the La 2/3 Sr 1/3 MnO 3 ͑LSMO͒ half-metal combined with BFO and epitaxially grown onto SrTiO 3 ͑001͒ substrates by pulsed laser deposition. We study the morphological, structural, electrical, and ma...
