Magnetic tunnel junctions using LaSrMnO ferromagnetic electrodes and PbZrTiO 3 piezoelectric barrier
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We report on the fabrication and tunneling characteristics of pulsed-laser deposited LaSrMnO (LSMO)/PbZrTiO(PZT)/LSMO/SrTiO3 magnetic tunnel junctions. The trilayer films show magnetic onset at about 360 K with ferromagnetic hysteresis and uniaxial magnetic behavior at room temperature. The microscopic studies show that the effective barrier thickness is reduced due to the presence of defects in the barrier region. Tunneling magnetoresistance measurements were performed on several samples. Our results suggest that the asymmetric deformation of the barrier potential profile induced by the ferroelectric polarization of PZT influences the tunneling characteristics and can be used for electrically controlled readout in quantum computing schemes. I. INTRODUCTION
Magnetic tunnel junctions (MTJs) consisting of two ferromagnetic electrodes separated by a thin insulating barrier show large TMR making them potential candidates for memory applications. While various materials are exploited for obtaining an effective barrier for the spin-polarized tunneling, the multiferroic materials are being considered to exploit multifunctional properties in a single barrier.1–4 A simple way to exploit this multifunctional character is to design magnetic tunnel junctions integrating a nanometric ferroelectric or piezoelectric film as the tunnel barrier. These tunnel junctions are interesting because they may exhibit effect of ferroelectric polarization on tunneling conductance5–7 and on TMR.8,9 The main problem is to integrate the ferroelectric–piezoelectric materials, which should have the stability of ferroelectric or piezoelectric behavior at a small thickness of a tunnel barrier. The initial results show that perovskites, such as SrTiO3 (STO), show MTJ behavior when used as a tunnel barrier.8 The purpose of the present research is to create a dynamic MTJ, in which the barrier region can further be tuned by an electric field. This allows one to study the influence of piezoelectricity of interlayer, such as Pb(ZrxTi1–x)O3 (PZT), on the tunneling properties that make our studies interesting compared to previously studied interlayers. This opens a next generation of multifunctional spintronic devices whose properties can be manipulated by several stimuli, as described elsewhere.9 Doped perovskite manganites that show ferromagnetism above room temperate10 have received a great deal
II. EXPERIMENTAL
All layers, LSMO/PZT/LSMO, were in situ deposited on STO substrates using the ultrahigh vacuum (UHV) pulsed laser deposition technique. Multitarget carousel is
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0378 J. Mater. Res., Vol. 24, No. 10, Oct 2009
http://journals.cambridge.org
of interest because of their potential use for various device applications such as infrared detectors, magnetic field sensors,11,12 and high density memory applications. In recent years, manganite films, such as (La1–xSrx) MnO3 (LSMO), have stimulated intense studies due to their colossal magnetoresistance (MR) effe
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