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Non-Equilibrium Investigations of Canted Antiferromagnet Under Flowing Electrical Current
| Content Provider | Semantic Scholar |
|---|---|
| Author | Lee, Yonghun |
| Copyright Year | 2018 |
| Abstract | Strontium iridium oxide (Sr2IrO4) is an antiferromagnetic Mott insulator, driven by strong spin-orbit coupling and Coulomb repulsion. The spin-orbit interaction locks the IrO6 octahedra rotation and Ir magnetic moment canting. Recently, the current-induced metal-insulator transition in bulk single crystals of Sr2IrO4 was reported [1]. According to the study, the coupling of flowing electrical current and canting angle leads to an a-axis lattice expansion of up to 1%; this nonlinear change in lattice and magnetic structure drives a unique resistive switching behavior. For the 2018 PARADIM REU Program, we tested the electrical control of Sr2IrO4 in a thin film platform and clarified the physical mechanisms behind the current-induced metal-insulator transition of Sr2IrO4. Summary of Research: Epitaxial Sr2IrO4 thin films, grown by molecular-beam epitaxy on LSAT <001>, NGO <001>, and STO <001> substrates, were tested at the probe station equipped with Keithley 4200A-SCS Parameter Analyzer and 4225-PMU Ultra-Fast I-V Module (for pulsed-IV). For low temperature measurements, the probe station was cooled down to T = 80 K by liquid nitrogen. The current-induced electrical control implies that the current density required for metal-insulator transition should be comparable across Sr2IrO4 samples with different sizes. Comparison with the reported single crystal data [1], along with simple calculations of the ratio of cross-sectional area of current flow, gave a rough estimation on the amount of current required for switching in Sr2IrO4 thin film (~ 1 μA). However, no nonlinear behavior was observed with Sr2IrO4 thin films within the compliance limit (10 mA) imposed by the probe station electronics. It was clear that the mechanism of switching in epitaxial thin films is different from bulk single crystals, because of the huge disparity of current density required for resistive switching. Subsequent experiments were done with smaller film devices fabricated and patterned by platinum electrodes on each side. The devices’ dimension was in the order of 10 μm × 10 μm. Film devices with smaller cross-sectional area of current flow enabled larger current density input, and we were able to induce the nonlinear resistive switching both at T = 300 K and T = 80 K. Results and Conclusions: Switching behaviors and Joule heating effect observed at room temperature can be explained by the oxygen vacancy migration-driven resistive switching of oxide thin films. Under a large electric field, oxygen vacancies migrate, cluster, and form conducting filaments in oxide films [2]. If the filaments are stable after an initial voltage sweep, the film enters into a non-volatile lowresistance state—memory switching (Figure 1). On the other hand, if the filaments cannot be maintained during the voltage sweep, the low-resistance state is volatile and only maintained at the large voltage bias, returning to the original high-resistance state below a certain voltage threshold—threshold switching (Figure 2). The migration of oxygen vacancies can be modeled as a ‘hopping’ process in a periodic potential. The hopping rate is very slow under E-field alone. Joule heating accelerates the hopping rate by creating a large thermal |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.cnf.cornell.edu/doc/2018reuFinalReports_Lee.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
