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Epitaxial Strain and Ferroelectric Field-effect Modulation of Magnetotransport in Correlated Oxide Thin Films
In this work, the effect of epitaxial strain and ferroelectric field-effect modulation on the magnetotransport properties of 3d Sm 0.5Nd0.5NiO3 (SNNO) and 5d SrIrO3 (SIO) thin films have been thoroughly examined. As a bulk, SNNO is a charge-transfer insulator which exhibits second-order metal-insulator transition (MIT) around room temperature. By carefully choosing the substrates, we found that the MIT temperature (T MI) of the SNNO films increases with increasing tensile strain. Combination of Hall effect measurement and low temperature transport reveals significantly enhanced electron localization in SNNO when under a large tensile strain. SIO is a paramagnetic semimetal with strong spin-orbit coupling (SOC). For the SIO thin films grown on (001) SrTiO3 (STO) substrates, we observed total charge compensation attributed to moderate compressive strain. As a manifestation of possession of strong SOC, weak anti-localization has also been observed at low temperature. By probing the temperature and film thickness dependence of spin relaxation, we have examined the spin relaxation mechanism. ^ Ferroelectric field-effect approach has been adopted by synthesizing Pb(ZrxTi1-x)O 3 (PZT)/SNNO and PZT/SIO heterostructures. Working with a prototype ferroelectric field-effect transistor, we have demonstrated robust resistance switching up to 75% and nonvolatile modulation of T MI for PZT/SNNO grown on LaAlO3 substrate. However, the PZT hardly has any effect on the SNNO for the case of STO. In both systems, we also observed a pronounced relaxation of off state resistance, showing a thermally activated behavior. The time dynamics and thermal response of the retention behavior suggest that strain-induced oxygen vacancies play a critical role in the ferroelectric field-effect instability. Meanwhile, we have also demonstrated a resistance modulation of 25% at 300 K in PZT/SNNO heterostructures. In addition, using the polarization field of PZT, we have demonstrated tunable spin relaxation. This suggests that the ferroelectric field-effect approach is a promising route to realize spintronics devices, such as the spin field-effect transistor. ^
Physics|Condensed matter physics
Zhang, Le, "Epitaxial Strain and Ferroelectric Field-effect Modulation of Magnetotransport in Correlated Oxide Thin Films" (2018). ETD collection for University of Nebraska - Lincoln. AAI10844114.