Structural and Magneto-Electric Properties of Pulsed Laser Deposited Ferroelectric/Ferromagnetic Heterostructures
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Structural and Magneto-Electric Properties of Pulsed Laser Deposited Ferroelectric/Ferromagnetic Heterostructures R. Martínez1, Ashok Kumar1, R. Palai1,2, and R.S. Katiyar1,2 1. Department of Physics, University of Puerto Rico, PR 00931, USA. 2. Institute for Functional Nanomaterials, University of Puerto, USA. ABSTRACT Asymmetric superlattices (SLs) with ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric Ba0.7Sr0.3TiO3 (BST) as constitutive layers were fabricated on conducting LaNiO3 (LNO) coated (001) oriented MgO substrates using pulsed laser deposition (PLD). The crystallinity, ferroelectric and magnetic properties of the SLs were studied over a wide range of temperatures and frequencies. The structure exhibited ferromagnetic behavior at 300K, and ferroelectric behavior over a range of temperatures between 100K and 300K. The dielectric response as a function of frequency obeys normal behavior below 300 K, whereas it follows Maxwell–Wagner model at elevated temperatures. The effect of ferromagnetic LSMO layers on ferroelectric properties of the SL indicated strong influence of the interfaces. The asymmetric behavior of ferroelectric loop and the capacitance-voltage relationship suggest development of a built field in the SLs due to high strain across the interfaces. Keywords: ferroelectric, ferromagnetic, superlattice, Maxwell-Wagner. INTRODUCTION Barium strontium titanate Ba0.7Sr0.3TiO3 (BST) ceramic is a typical ferroelectric material which is known to adopt the ABO3 type structure, and displays a paraelectric-ferroelectric transition at a Curie temperature around 312 K. Presently there is a great deal of interest in ferroelectric perovskite BST thin films because these are promising candidates for the next generation of dynamical random access memory (DRAM) capacitors, and tunable microwave devices, owing to their excellent ferroelectric responses and dielectric behavior. At room temperature, BST thin film has a high dielectric constant and high tunability, but their characteristics change when grown on different substrates [1,2]. Meanwhile, lanthanum strontium manganese oxide La0.7Sr0.3MnO3 (LSMO) ceramic is a typical ferromagnetic perovskite with a phase transition from a ferromagnetic metal to a paramagnetic insulator around 370 K with a peak in the resistivity; this has attracted much attention. The functional properties of LSMO thin films, such as, good ferromagnetic metallic phase with colossal magnetoresitance (CMR), and relatively low resistivity, have made them interesting candidates for hard disk drives (HDD), video tape recorders (VTR), and spintronic devices [3,4]. Recently artificial SLs provided an opportunity to design horizontal structures that exhibited multiferroism from a combination of two or more distinct compounds consisting of alternate layers of ferromagnetic and ferroelectric materials segregated on the nanoscale level [5,6]. In this sense, coupling between the integrated BST/LSMO heterostructures offers a great potential for new multifunctional devices applications, su
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