Ion irradiation effect in complex oxides: Another degree of freedom or complexity?

Inter-relations among charge, spin, orbital and lattice parameters are largely demonstrated in multi-functional oxide materials, which exhibit a variety of exotic properties, ranging from superconductivity, insulator-metal transition, colossal magnetoresistance, charge ordering, and orbital ordering, etc. In particular, tilting a delicate energy balance in lattice interactions and kinetics, achieved by temperature, pressure or chemical control, may result in exotic phenomena in these systems. However, fine-tailoring such interactions has proven difficult. 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. In this contribution, we show that ion irradiation can modify the magnetic and electrical transport properties in a broad variety of materials, including spinel NiCo2O4, perovskite BiFeO3, SrRuO3 and LaNiO3 [1-4]. Diverse magnetic, structure and magneto-transport modifications, which are inaccessible by conventional film growth methods, have been obtained. For instance, the transport in LaNiO3 can be driven from metallic phase into an Anderson insulator by directly tuning the electronic mean free path via irradiation-induced disorder [4]. In BiFeO3, we have obtained a super-tetragonal phase with the largest c/a ratio ~ 1.3 that has ever been experimentally achieved in BiFeO3 [2]. This may lead to strong polarization enhancement. By comparing the effect in different materials, we will also point out the complexity in understanding the tailoring of oxides by ion beams.

Reference
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