Magnetoelastic coupling in strained La0.7Ca0.3MnO3//BaTiO3 Thin Films
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Magnetoelastic coupling in strained La0.7Ca0.3MnO3//BaTiO3 Thin Films A. Alberca1, J. Azpeitia-Urkia1, J. Tornos2, C. Munuera1, F. J. Mompean1, N. M. Nemes2, C. Leon2, A. Hernando3, Titusz Fehér4, Ferenc Simon4, B. J. Kirby5, M. R. Fitzsimons6, J. Santamaria2 and M. Garcia-Hernandez1 1
Instituto de Ciencias de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, ES-28049 Madrid (Spain) 2 Departamento de Física Aplicada III, Facultad de Física, Universidad Complutense, Ciudad Universitaria, ES-28040 Madrid (Spain) 3 Departamento de Física de Materiales, Facultad de Física, Universidad Complutense, Ciudad Universitaria, ES-28040 Madrid (Spain) 4 Department of Physics, Budapest University of Technology and Economics, Budafoki ut 8, H1111 Budapest (Hungary) 5 Center for Neutron Research, NIST, Gaithersburg, MD 20899 (U.S.A.) 6 Los Alamos National Laboratory, Los Alamos, NM 87545 (U.S.A.) ABSTRACT In this paper, we explore the interfacial effects appearing in highly strained La0.7Ca0.3MnO3 (LCMO) ultra-thin films (10-12nm) grown on BaTiO3 (BTO) ferroelectric substrates. The strong tendency to phase separation of this optimally doped manganite contributes to the exotic phenomena observed in magnetism and transport experiments: the socalled Matteucci magnetic loops, magnetic granularity and a second metal insulator transition are observed between 50K and the LCMO Curie temperature, 180K. All these properties define the multiferroic character of these heterostructures, which in LCMO//BTO system is strongly linked to magnetoelastic coupling. INTRODUCTION A recent common approach to improving storage density is the use of multiferroic materials and heterostructures [1-4] allowing the use of small voltages (instead of magnetic fields or spin polarized curents) to write in a memory unit. Presently, many of the actively studied multiferroic heterostructures combine different types of complex oxides, which comprise two or more transition metal cations (usually 3d) and oxygen [5-7]. In this paper, we consider a particular case of multiferroic heterostructures consisting of a ferromagnetic LCMO thin film layer grown on ferroelectric BTO substrates. Optimal doped manganite LCMO is a strongly correlated compound well known for exhibiting Colossal Magnetoresistance (CMR) effect. LCMO is particularly prone to phase separation [8] and, therefore, susceptible of being strongly affected by substrate strain and ferroelectric polarization. BTO is a well studied ferroelectric of the perovskite class [9]. EXPERIMENT AND DISCUSSION We compare LCMO thin films on ferroelectric BTO substrates with those grown on nonferroelectric SrTiO3 (STO). Thin LCMO films (12 nm thick) were prepared either on unpoled BTO (001) or on STO (100) crystalline substrates by sputtering with a highly oxidizing plasma (3.4 mbar oxygen atmosphere) at temperatures (900 ˚C) well above the BTO ferroelectric Curie point. We refer to these samples as LCMO//BTO and LCMO//STO, respectively. The deposition
rate was very slow (around 1nm/min) and strict annealing (several
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