Speaker
Description
Complex oxides host a multitude of novel phenomena in condensed matter physics, such as various forms of multiferroicity, colossal magnetoresistance, quantum magnetism, and superconductivity. This is largely due to the strong correlation between charge, spin, orbital, and lattice parameters. Specifically, tilting the delicate energy balance in lattice interactions and kinetics, achieved by temperature, strain, or chemical doping, can result in significant modifications in these materials [1]. In this context, defect engineering by ion irradiation, which can introduce strain and electronic disorder, has emerged as a powerful technique to fine-tune complex phases of oxide thin films. The induced uniaxial strain, manifested as the elongation of the out-of-plane lattice spacing, is not limited to available substrates, the conventional and well-known strain engineering approach. In this contribution, we will introduce the tailoring of oxide thin films by ion irradiation, with examples including the modification of magnetic and magneto-transport properties of SrRuO3 [2, 3], and ferroelectric properties of BiFeO3 [4, 5]. The irradiated SrRuO3 films exhibit a pronounced topological Hall effect in a wide temperature range from 5 to 80 K, which can be attributed to the emergence of Dzyaloshinskii–Moriya interaction resulting from artificial inversion symmetry breaking associated with lattice defect engineering. In BiFeO3, we have obtained a super-tetragonal phase with the largest c/a ratio (~1.3) ever experimentally achieved. By controlling the ion energy, we can create a continuous in-plane charged antiphase boundaries around the implanted depth. The antiphase interface reveals a variety of atomic bonding configurations, showing the atomically sharp 180° polarization reversal across the boundary. We show that ion irradiation is a very versatile pathway for tailoring oxide functionalities, analogous to ion-implantation doping for conventional semiconductors. It is worth noting that ion beam technology has been well-developed for microelectronics. Once the principle of concept is approved, the approach can be easily scaled up and integrated into the industry production line.
[1] D. S. Aidhy and K. Rawat, Coupling between interfacial strain and oxygen vacancies at complex-oxides interfaces, J. Appl. Phys. 129, 171102 (2021).
[2] C. Wang, et al., Defect-Induced Exchange Bias in a Single SrRuO3 Layer, ACS Appl. Mater. Interfaces 10, 27472 (2018).
[3] C. Wang, et al., Topological Hall Effect in Single Thick SrRuO3 Layers Induced by Defect Engineering, Adv. Electron. Mater. 6, 2000184 (2020).
[4] C. Chen, et al., Controllable defect driven symmetry change and domain structure evolution in BiFeO 3 with enhanced tetragonality, Nanoscale 11, 8110 (2019).
[5] X. Cai, et al., In-plane charged antiphase boundary and 180° domain wall in a ferroelectric film, Nature Communications 14, 8174 (2023).