Combining half-metals and multiferroics into epitaxial heterostructures for spintronics

Abstract

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...

Polaronic Transport Induced by Competing Interfacial Magnetic Order in aLa0.7Ca0.3MnO3/BiFe

“…In these novel systems, different degrees of freedom (DOFs) (e.g., charge, spin, and orbital) are coupled at a single interface between two different oxide layers to form a new state that displays properties dramatically different from those of the individual layers [4][5][6][7][8]. Particular attention has been given to the coupling between ferromagnetic (FM), antiferromagnetic (AFM), and ferroelectric (FE) orders, as this could reveal new routes to realizing strong magnetoelectric coupling [1][2][3][9][10][11].Heterostructures consisting of manganite and multiferroic layers are particularly promising in this regard. The most extensively studied combination [2,3,9,10,12] consists of the colossal magnetoresistive manganite La 0.7 Sr 0.3 MnO 3 (LSMO) [or the similar compound La 0.7 Ca 0.3 MnO 3 (LCMO)], which is ferromagnetic below a critical temperature T c , and the canonical multiferroic BiFeO 3 (BFO), which has coexisting coupled AFM and FE phases in which the magnetization can be switched by an applied electric (E) field [13].…”

“…In these novel systems, different degrees of freedom (DOFs) (e.g., charge, spin, and orbital) are coupled at a single interface between two different oxide layers to form a new state that displays properties dramatically different from those of the individual layers [4][5][6][7][8]. Particular attention has been given to the coupling between ferromagnetic (FM), antiferromagnetic (AFM), and ferroelectric (FE) orders, as this could reveal new routes to realizing strong magnetoelectric coupling [1][2][3][9][10][11].…”

“…Particular attention has been given to the coupling between ferromagnetic (FM), antiferromagnetic (AFM), and ferroelectric (FE) orders, as this could reveal new routes to realizing strong magnetoelectric coupling [1][2][3][9][10][11].…”

“…The most extensively studied combination [2,3,9,10,12] consists of the colossal magnetoresistive manganite La 0.7 Sr 0.3 MnO 3 (LSMO) [or the similar compound La 0.7 Ca 0.3 MnO 3 (LCMO)], which is ferromagnetic below a critical temperature T c , and the canonical multiferroic BiFeO 3 (BFO), which has coexisting coupled AFM and FE phases in which the magnetization can be switched by an applied electric (E) field [13]. The combination of these materials thus has great potential for exhibiting novel phenomena by coupling different FM, AFM, and FE phases across the interface.…”

Control of ferroelectricity and magnetism in multi-ferroic BiFeO 3 by epitaxial strain

“…To conduct a detailed study on the numerous properties of BFO and their response to epitaxial strain, a series of films on various substrates imposing a range of misfit strains from −2.5% to +1.3% were grown by pulsed laser deposition [21][22][23]. The substrates used were (La, Sr)(Al, Ta)O 3 (LSAT), SrTiO 3 (STO), DyScO 3 (DSO), GdScO 3 (GSO), SmScO 3 (SSO), NdScO 3 (NSO) and PrScO 3 (PSO).…”