Electro-resistive Memory Effect in Colossal Magnetoresistive Films and Performance Enhancement by Post-annealing
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Electro-resistive Memory Effect in Colossal Magnetoresistive Films and Performance Enhancement by Post-annealing Shangqing Liu, Naijuan Wu, Alex Ignatiev, Gustavo Tavizon and Christina Papagianni Space Vacuum Epitaxy Center, Texas Center for Superconductivity and Department of Physics, University of Houston, Houston, Texas 77204-5507, USA ABSTRACT Colossal magnetoresistive thin films have shown a large electric-pulse-induced resistivity change effect in zero magnetic field and at room temperature. The resistance of such films can be both decreased and increased through multiple nonvolatile intermediate levels by short electrical pulses. The effect provides a potential to develop a novel nonvolatile memory with high density, fast speed, and low power-consumption. An example of this effect has been seen for Pr0.7Ca0.3MnO3 films within which the thermal behavior of the film revealed a method for signal enhancement through annealing. An increase of 700% of the resistance ratio has been demonstrated for a film annealed at 170oC for 30 min. The effect is also observed to be active at room temperature but inefficient at low temperatures, which is interestingly contrary to the behavior of the colossal magnetoresistance effect and provides a clue to understanding the effect.
INTRODUCTION The hysteretic behavior of the resistivity of colossal magnetoresistive (CMR) materials under magnetic field has incited interest to develop new nonvolatile memory devices [1,2]. The enforced spin alignment which causes an insulator-metal transition with dramatic resistivity change requires high magnetic field to drive the system, and such spin alignment which provides nonvolatile resistance values needs low operating temperature to weaken the unbinding/delocalizing force to the charge carriers. These requirements are hindrances to technology applications of the CMR materials. Much effort has been made to get large, low field (or small external stimulation), room temperature magnetoresistance and hysteresis [3-6]. The recently reported electrical-pulse-induced resistance (EPIR) effect presents a way to obtain a large resistance change and hysteresis in CMR materials under small external stimulation [7]. By applying short electrical pulses to CMR thin films, the resistance and resistance hysteresis values of the films can be changed in zero applied magnetic field and at room temperature. These changes are nonvolatile and reversible, and present an avenue for making a new kind of nonvolatile memory as described here.
THIN FILM GROWTH Single-crystal and polycrystalline films of Pr0.7Ca0.3MnO3 (PCMO) were processed into test samples. First, conductive bottom layers of YBa2Cu3O7 (YBCO) or Pt with thickness P3.26.1
ranging from 600 nm-1 µm and 60 nm - 400 nm, respectively, were deposited onto (100) LaAlO3 (LAO) substrates by pulsed laser deposition (PLD). The YBCO layer was used both as a conductive electrode and as an atomic template for PCMO epitaxial deposition. The Pt layer was used as a control test bottom electrode. Then PCMO films of th
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