In-Plane Transport of Doped Manganite Trilayers
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In-Plane Transport of Doped Manganite Trilayers Lisa Berndt Alldredge School of Applied & Engineering Physics, Cornell University, Ithaca, NY 14853 Y. Suzuki Dept. of Materials Science & Engineering, Cornell University, Ithaca, NY 14853 †presently at Dept. of Materials Science & Eng., UC Berkeley, Berkeley, CA 94720 ABSTRACT We have synthesized and characterized doped manganite trilayers composed of La0.7Sr0.3MnO3 (LSMO) and La0.7Ca0.3MnO3 (LCMO). Because of the isostructural nature of the Sr and Ca doped manganites, trilayers exhibit good epitaxy as observed in X-ray diffraction. Magnetization measurements reveal magnetization values consistent with bulk values. In-plane transport of these trilayers reveals anisotropic magnetoresistance and high field negative magnetoresistance attributed to the suppression of spin fluctuations at high fields. INTRODUCTION Colossal magnetoresistance (CMR) materials consist of a group of doped perovskite manganites of chemical composition A1-x Bx MnO3 (where A = trivalent rare earth and B = divalent alkaline earth). While the phase diagram of the doped manganites is rather complicated and includes ferromagnetic, antiferromagnetic, and paramagnetic phases, insulating and metallic phases and charge ordered phases, the subclass of materials that exhibit a transition from a ferromagnetic metallic phase to a paramagnetic insulating one are known as CMR materials. They exhibit large changes in resistance under an applied magnetic field and thus have been the subject of extensive research due to their possible application in computer read/write heads and storage devices. Magnetoresistance (MR) values as high as 80% in LCMO at ~200K and 35% in LSMO at ~330K have been observed under high magnetic fields (~5 Tesla). Many groups have studied CMR and CMR-based devices in the hopes of obtaining large magnetoresistances at low fields and at room temperature. Some research groups have focused on fabricating CMR-based magnetic tunnel junctions to this end. Initial studies of CMR tunnel junctions have shown junction magnetoresistance (JMR) behavior on field scales as low as ~50 Oe [1,2]. Subsequent studies have shown JMR values as high as 100% at 13K [3,4]. However, JMR decreases rapidly with increasing temperature and vanishes by room temperature. In magnetic tunnel junctions, the interface quality, tunnel barrier quality, surface/interface roughness, ferromagnetic electrode quality,
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magnetic domain walls as well as the intrinsic behavior of ferromagnetic surfaces/interfaces greatly affect the JMR. It has greatly complicated the interpretation of transport data and may contribute to the premature suppression of spin polarized tunneling to temperatures below the Curie temperature of the CMR electrodes. More recently, near room temperature operation of CMR-based tunnel junctions has also been observed by Obata et al. [5]. To minimize interface disorder, Goodenough’s group incorporated a tunnel barrier of (La0.85Sr0.15)MnO3 between La0.7Sr0.3MnO3 electrodes and obtained JMRs at temp
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