Defect Control of Conventional and Anomalous Electron Transport at Complex Oxide Interfaces

Abstract

Using low-temperature electrical measurements, the interrelation between electron transport, magnetic properties, and ionic defect structure in complex oxide interface systems is investigated, focusing on NdGaO3/SrTiO3 (100) interfaces. Field-dependent Hall characteristics (2–300 K) are obtained for samples grown at various growth pressures. In addition to multiple electron transport, interfacial magnetism is tracked exploiting the anomalous Hall effect (AHE). These two properties both contribute to a nonlinearity in the field dependence of the Hall resistance, with multiple carrier conduction evident below 30 K and AHE at temperatures ≲10K . Considering these two sources of nonlinearity, we suggest a phenomenological model capturing the complex field dependence of the Hall characteristics in the low-temperature regime. Our model allows the extraction of the conventional transport parameters and a qualitative analysis of the magnetization. The electron mobility is found to decrease systematically with increasing growth pressure. This suggests dominant electron scattering by acceptor-type strontium vacancies incorporated during growth. The AHE scales with growth pressure. The most pronounced AHE is found at increased growth pressure and, thus, in the most defective, low-mobility samples, indicating a correlation between transport, magnetism, and cation defect concentration.

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Plain Language Summary

Crystal defects are known to have a significant impact on the physical bulk properties of materials. However, the role of defects in the novel properties arising specifically at the interfaces of materials such as transition-metal oxides is still being debated. Here, we experimentally analyze the transport properties of the electron system arising at the single crystalline interface between two oxides: NdGaO3 and SrTiO3 . We recover a fascinating combination of properties induced by defects—metallicity and magnetism—that are absent in the bulk materials.

Using magnetotransport measurements, we characterize the ionic defect structure and analyze the interfacial magnetism over a wide temperature range (2–300 K). In particular, we find clear indications of multicarrier conduction and magnetic effects in the Hall resistance, which are commonly referred to as conventional and anomalous Hall effects, respectively. We develop a model, disentangle these two types of Hall effects, and fully describe the entire complex magnetic-field behavior of the Hall coefficient. For different samples grown in different conditions, we infer (i) the ionic defect structure and (ii) the magnetic properties. We accordingly reveal a systematic relation between these data sets. We find that magnetism is most pronounced in samples with a high density of strontium vacancies accompanied by a decrease in electron mobility.

Our results shed light on the important role of cationic defects at oxide heterointerfaces and pave the way for a more thorough understanding of the properties of the interfaces, both theoretically and experimentally, in oxides as well as other electronic systems.